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Slope Stability 2013 | Abstracts
Keynote addresses2 Pit slopes in weathered and weak rocks
C.D. Martin, University of Alberta, Canada; P.F. Stacey, Stacey Mining Geotechnical Ltd., Canada
3 Numerical analysis, slope design and in situ stress J. Sjöberg, Itasca Consultants AB, Sweden
4 Waterandslopestability–theapplicationofanewscience G. Beale, Schlumberger Water Services, UK
5 Globalslopeperformanceindex T.D. Sullivan, Pells Sullivan Meynink; and The University of New South Wales, Australia
6 Datagathering,interpretation,reliabilityandgeotechnicalmodels J.R.L. Read, CSIRO Earth Science and Resource Engineering, Australia
7 Excavationcontrol,managementofblastdamage,andqualitycontrol J.V. Simmons, Sherwood Geotechnical and Research Services, Australia
C. Fietze, Golder Associates Africa (Pty) Ltd, South Africa; A. Creighton, Rio Tinto, Australia; L.M. Castro, Golder Associates Ltd., Canada; R. Hammah, Golder Associates, Ghana
10 RockmassandstructuralmodellingforthelargeopenpitgoldminingprojectintheNorthernAndes:TheLaColosaproject,Colombia J. Horner, J. Weil, iC consulenten, Austria; J. Betancourt, A. Naranjo, P. Montoya, J. Sánchez, AngloGold Ashanti Colombia, Colombia
11 Anextensionalmechanismofinstabilityandfailureinthewallsofopenpitmines M.C. Bridges, AMC Consultants Pty Ltd, Australia
12 Rapidcharacterisationofpotentiallyhazardousblocksinopenpitmining M.K. Elmouttie, G.V. Poropat, G. Krähenbühl, P. Dean, CSIRO Earth Science and Resource Engineering, Australia
13 Reliabilityofstrengthestimatesbasedonlimitedlaboratorydata M-H. Fillion, J. Hadjigeorgiou, Lassonde Institute of Mining, University of Toronto, Canada
Table of Contents
Slope Stability 2013 | Abstracts
14 Interpretinglocalcriticalorientationsofstructuralweaknessinrelationtostress and dilatancy in rock slopes J.V. Smith, School of Civil, Environmental and Chemical Engineering, RMIT University, Australia
15 Combiningfieldmethodsandnumericalmodellingtoaddresschallengesincharacterisingdiscontinuitypersistenceandintactrockbridgesinlargeopenpit slopes Z. Tuckey, Coffey Mining Pty Ltd, Australia; D. Stead, Department of Earth Sciences, Simon Fraser University, Canada; E. Eberhardt, Department of Earth and Ocean Sciences, University of British Columbia, Canada
16 Discussiononhowtoclassifyandestimatestrengthofweakrockmasses L.M. Castro, J. Carvalho, Golder Associates Ltd., Canada; G. Sá, Vale, Brazil
17 Structuraldatabiasinthedigitalage M.J. Fowler, Pells Sullivan Meynink, Australia
18 Benchbermdesignusingprobalistickeyblockanalysis E. Hormazabal, SRK Consulting (Chile) S.A., Chile
19 Ongoing research into anisotropic rock masses using numerical modelling K.G. Mercer, Australian Centre for Geomechanics, The University of Western Australia, Australia
20 Geochemistryandgeotechnicalmodels–acasestudyfromtheproposedKempfieldSilverProject,Bathurst,NewSouthWales H. Baxter, T. Rutherford, R. Bertuzzi, Pells Sullivan Meynink, Australia
22 Experimentalandnumericalassessmentofshearsurfacedamageusing3Dpoint clouds S. Karekal, G.V. Poropat, H. Guo, CSIRO Earth Science and Resource Engineering, Australia
23 Thedeterminationofjointroughnesscoefficientusingthree-dimensionalmodelsforslopestabilityanalysis D.H. Kim, I. Gratchev, School of Engineering, Griffith University, Australia; G.V. Poropat, CSIRO Earth Science and Resource Engineering, Australia
24 Geotechnical and geological model applied to crushing processes in open pit mines P. Peña, Ingeniería de Rocas Ltda., Chile; R. Fuenzalida, TECK Carmen de Andacollo, Chile; R. Villarroel, P. Merino, Ingeniería de Rocas Ltda., Chile; M. Tapia, TECK Carmen de Andacollo, Chile; P. Casanova, Geoatacama, Chile
26 Structuralgeologymodelling:asummaryondataintegrityandmodellingmethods K.M. Rees, J. Graaf, Golder Associates Pty Ltd, Australia
27 Astatisticalapproachtoaccountforelevatedlevelsofuncertaintyduringgeotechnical design R.D.H. Thomas, Coffey Mining Pty Ltd, Australia
28 PreliminaryreviewofthegeotechnicalcharacteristicsandshearstrengthestimatesofsmallscaleanisotropicwaveformformationsofthePilbara,Western Australia S. Tokimoto, School of Civil and Resource Engineering, The University of Western Australia; K.G. Mercer, Australian Centre for Geomechanics, The University of Western Australia, Australia
29 Dissectionofapit–casestudy A.J. Troy, Terra Firma Australia Pty Ltd, Australia
dewatering system M. Bester, E. Nel, G.M. Mc Gavigan, Anglo American Kumba Iron Ore, South Africa
32 Watermanagementforslopestabilisation–anexamplefromPeru C. Pérez, Schlumberger Water Services, Peru; V. Pérez, Minera Yanacocha S.R.L., Peru; G. Beale, Schlumberger Water Services, UK; D. Ríos, F. Soto, Minera Yanacocha S.R.L., Peru
33 CockatooIslandstage3:seawallfailureandremediation P.K. Wong, Coffey Geotechnics Pty Ltd, Australia; P. Petropulos, Coffey Mining Pty Ltd, Australia
34 Casehistory:deep-seatedslopefailureinweakrocks,ElTapadopitnorthwall,Yanacochaoperation G.A. Becerra Abregu, E. Valencia Jeri, E. Garcia, Minera Yanacocha S.R.L, Peru; P. Yuan, Golder Associates Inc., USA; T. Byers, Newmont Mining Corporation, USA
35 PitslopedepressurisationinvestigationforanopencutironoremineinthePilbara A. Dodman, G. Beale, Schlumberger Water Services, UK; J. Rodriguez, Schlumberger Water Services, Australia; A. Cottrell, J. Youngs, BHP Billiton, Australia
Slope Stability 2013 | Abstracts
36 Approachtogroundwaterandporewaterpressuremodellingfordifferentgeotechnicalconditionsinopenpitslopestabilityanalysis H. El-Idrysy, SRK Consulting (UK) Ltd, UK
37 Acasestudyonactualwaterpressuremeasurementsatanopenpitexcavatedinstrong,tightrockandtheimplicationsforslopedesign M. Rougier, L.M. Castro, Golder Associates Ltd., Canada; D. Birchall, Barrick Gold, Canada
Uncertainty in design39 Anapplicationofareliabilitybasedmethodtoevaluateopenpitslopestability
M. Valerio, C. Clayton, S. D’Ambra, C. Yan, Golder Associates Ltd., Canada
40 Riskevaluationofslopeconsideringmechanicalandhydrauliccharacteristicsofunsaturatedsoils Y-K. Song, J-R. Oh, M.S. Jung, Y.J. Son, National Disaster Management Institute, Korea
41 Analysisoffailuresinopenpitminesandconsiderationoftheuncertaintywhenpredictingcollapses A.G. Cabrejo-Liévano, GroundProbe Pty Ltd, Australia
42 ManagingslopeperformanceinuncertaingeologicalconditionsatMeanduMine, Queensland J.V. Simmons, Sherwood Geotechnical and Research Services, Australia; D.C. Edwards, Downer EDI Mining Pty Ltd, Australia; N. Ferdinands, Stanwell Corporation Limited, Australia
43 Iterativegeotechnicalpitslopedesigninastructurallycomplexsetting:acasestudyfromTomPrice,WesternAustralia D.S. Lucas, Mining One Consultants, Australia; P.J.H. de Graaf, Rio Tinto Iron Ore, Australia
44 SlopedesignatCuajonePit,Peru E. Hormazabal, SRK Consulting (Chile) S.A., Chile; R. Veramendi, J. Barrios, Southern Peru Cooper Corporation, Peru; G. Zuñiga, F. Gonzalez, SRK Consulting (Chile) S.A., Chile
47 Geotechnicalreliabilityassessmentofalargecounterfortretainingwall W. Deng, K. O’Neill, K. Luu, Aurecon Pty Ltd, Australia; K. Little, Baulderstone Construction, Australia
48 Towardsdevelopingamorerigoroustechniqueforbenchscaleslopestabilityanalysis in hard rock R. Teet, A. Vakili, A. de Veth, AMC Consultants Pty Ltd, Australia
Mine M. Fournier, R. Mercer, D. Yang, Knight Piésold Ltd., Canada; J. Miller, KGHM Inc., USA
51 Theuseofnumericalmodelling,slopemonitoringandoperationalprocedurestomanageslopedeformationsattheRanger3Pit D.R. Wines, Itasca Australia Pty Ltd, Australia; I. Hulls, Mining One Consultants, Australia; E. Woods, Energy Resources of Australia Ltd, Australia; A. Creighton, Rio Tinto, Australia
52 Incorporatingbrittlefractureintothree-dimensionalmodellingofrockslopes M. Havaej, A. Wolter, Simon Fraser University, Canada; D. Stead, Department of Earth Sciences, Simon Fraser University, Canada; Z. Tuckey, Coffey Mining Pty Ltd, Australia; L. Lorig, Itasca Consulting Group Inc., USA; E. Eberhardt, Department of Earth and Ocean Sciences, University of British Columbia, Canada
53 Openpitnumericalmodelcalibrationusingapseudothree-dimensionalradarmonitoringtechnique J. Severin, SRK Consulting (Canada) Inc., Canada; E. Eberhardt, Department of Earth and Ocean Sciences, University of British Columbia, Canada; S. Fortin, Teck Resources Ltd., Canada
54 Two-dimensionalandthree-dimensionaldistinctelementnumericalstabilityanalysesforassessmentofthewestwallcutbackdesignatOkTediMine,Papua New Guinea I.A. de Bruyn, SRK Consulting (Australasia) Pty Ltd, Australia; M.A. Coulthard, M.A. Coulthard and Associates Pty Ltd, Australia; N.R.P. Baczynski, Ok Tedi Mining Ltd, Papua New Guinea; J. Mylvaganam, SRK Consulting (Australasia) Pty Ltd, Australia
55 Three-dimensionalnumericalstabilityanalysisoftheOyuTolgoiopenpit M. Smithyman, H. Puebla, A. Chance, R. Beddoes, Golder Associates Ltd., Canada; A. Creighton, Rio Tinto, Australia
56 Three-dimensionalanalysisofpitslopestabilityinanisotropicrockmasses D.P. Sainsbury, Mining One Consultants, Australia; B. Sainsbury, Castlemaine Goldfields Ltd, Australia
Slope Stability 2013 | Abstracts
57 UDEC and RFPA2Dsimulationsontheinfluenceofthegeometryofpartially-spanningjointsonrockmechanicalbehaviour P.L.P. Wasantha, P.G. Ranjith, Civil Engineering Department, Monash University, Australia; T. Xu, Northeastern University, China
58 SlopestabilityanalysisatSiilinjärviMine S. Mononen, Yara Suomi Oy, Finland; H. Kuula, M. Lamberg, Pöyry Finland Oy, Finland
59 Theeffectofslopecurvatureinrockmassshearstrengthderivationsforstabilitymodellingoffoliatedrockmasses S. Narendranathan, R.D.H. Thomas, J.M. Neilsen, Coffey Mining Pty Ltd, Australia
60 Stabilityanalysesforalargelandslidewithcomplexgeologyandfailuremechanism using numerical modelling B. Wentzinger, D. Starr, S. Fidler, Golder Associates Pty Ltd, Australia; Q. Nguyen, ATC Williams Pty Ltd, Australia; S. Hencher, Steve Hencher Associates Ltd, UK
interpretationsandvisualisationmanagement A.B. Firman, C.D. Wiratno, S. Bahri, H. Timbul, PT Adaro Indonesia, Indonesia
63 Canfullwaveformtechnologyenhancetheuseofterrestriallaserscanningtomonitorrockslopedeformation? J.G. Williams, N.J. Rosser; Department of Geography, Durham University, UK; A. Afana, Department of Geography, Durham University; and 3D Laser Mapping Ltd, UK; G. Hunter, 3D Laser Mapping Ltd, UK; R.J. Hardy, Department of Geography, Durham University, UK
64 Experienceusingterrestrialremotesensingtechniquesforrockslopeperformanceassessment M. Sturzenegger, D. Willms, Klohn Crippen Berger Ltd., Canada; K. Pate, Seattle City Light, USA; B. Johnston, Tetra Tech Inc., USA
65 PowerfulrockfallincidentsatAl-Hadadescentandremedialmeasures B.H. Sadagah, Faculty of Earth Sciences, King Abdulaziz University, Saudi Arabia; M.S. Aazam, A. Al-Amri, O. Al-Hoseiny, A. Al-Harbi, Ministry of Transportation, Saudi Arabia
66 Innovativeuseofslopemonitoringradarasasupporttogeotechnicalmodellingofslopesinopenpitmines A.E.E. Escobar, Codelco El Teniente, Chile; P. Farina, L. Leoni, C. Iasio, N. Coli, IDS Ingegneria Dei Sistemi, Italy
Slope Stability 2013 | Abstracts
67 Slopemonitoringanddatavisualisationstate-of-the-art–advancingtoRioTintoIronOre’sMineoftheFutureTM P.J.H. de Graaf, S.D.N. Wessels, Rio Tinto Iron Ore, Australia
68 Applicationofgroundpenetratingradartoidentifythelocationsofsub-surfaceanomalies at Kansanshi Mine, Zambia N.K. Smith, First Quantum Minerals Ltd, Zambia
69 ApplicationofadvancedInSARtechniquestodetectverticalandhorizontaldisplacements J. Morgan, TRE Canada Inc., Canada; S. Raval, The University of New South Wales, Australia; B. Macdonald, G. Falorni, TRE Canada Inc., Canada; J. Iannacone, University of Modena and Reggio Emilia, Italy
70 Geotechnical risk management at Teck Coal A. Bidwell, A. Knight, Teck Coal Ltd., Canada; W.S. Anderson, Teck Resources Ltd., Canada
71 Undrainedbehaviourinspoilpiles A. Duran, Pells Sullivan Meynink, Australia
72 Shearstrengthparametersforassessinggeotechnicalslopestabilityofopenpitcoal mine spoil based on laboratory tests A.K. Kho, D.J. Williams, N. Kaneko, N.J.W. Smith, School of Civil Engineering, The University of Queensland, Australia
73 Flowfailureincoalstockpiles–howtoreducerisk P. Davies, S. Zargarbashi, L. McQueen, Golder Associates Pty Ltd, Australia
74 Integrationoffullwaveformterrestriallaserscannersintoaslopemonitoringsystem A. Afana, 3D Laser Mapping Ltd; and Durham University, UK; G. Hunter, J. Davis, 3D Laser Mapping Ltd, UK; N.J. Rosser, R.J. Hardy, J.G. Williams, Department of Geography, Durham University, UK
75 2011ManawatuGorgelandslide-technicalchallengesfacedduringremediation M.B. Avery, S. Bourke, Geovert Ltd, New Zealand
78 Earlydetectionofimpendingslopefailureinopenpitminesusingspatialandtemporalanalysisofrealapertureradarmeasurements G.J. Dick, E. Eberhardt, Department of Earth and Ocean Sciences, The University of British Columbia, Canada; D. Stead, Department of Earth Sciences, Simon Fraser University, Canada; N.D. Rose, Piteau Associates Engineering Ltd., Canada
Slope Stability 2013 | Abstracts
79 Geohazardmitigationinremoteandruggedterrain U.K. Gunasekera, Rio Tinto Australia, Australia
80 Stabilisationoflandslidesusinggravityfedsiphonandelectro-pneumaticpumpedwells:twoexamplesofslopestabilisationprojectsfromtheUnitedKingdomandCzechRepublic J.K. Holliday, Aurecon Australia Pty Ltd, Australia; A.R. Clark, Independent consultant, UK; D.S. Fort, Atkins, UK; A. Gillarduzzi, High Point Rendel, UK; S. Bomont, TPGEO, France
81 Riskmanagementandremediationofthenorthwallslip,WestAngelasMine,Western Australia G.G. Joass, R. Dixon, T. Sikma, S.D.N. Wessels, J. Lapwood, P.J.H. de Graaf, Rio Tinto Iron Ore, Australia
82 ApplicationofradarmonitoringatSavageRiverMine,Tasmania G.K. Macqueen, E.I. Salas, B.J. Hutchison, Grange Resources (Tasmania) Pty Ltd, Australia
83 Slopestabilitystudyinopenpitandundergroundminesbymeansofforensicanalysisandradarinterferometry O. Mora, Altamira Information, Spain; I. Álvarez, Universidad de Oviedo, Spain; E. Amor Herrera, Hullera Vasco-Leonesa, Spain
84 StabilityanalysisandremedialdesignoftworoadcuttingsinNorthQueensland based on remote geotechnical mapping using digital photogrammetry I. Ortega, P.W. Booth, J. Darras, Golder Associates Pty Ltd, Australia
85 Hangingwallandfootwallslopestabilityissuesinsublevelcaving B-M. Stöckel, K. Mäkitaavola, Luossavaara-Kiirunavaara AB, Sweden; J. Sjöberg, Itasca Consultants AB, Sweden
86 AnevaluationoftheCUSUMandinversevelocitymethodsoffailurepredictionbasedontwoopenpitinstabilitiesinthePilbara J. Venter, A. Kuzmanovic, S.D.N. Wessels, Rio Tinto Iron Ore, Australia
87 SlopestabilisationprogramatWestGully,PTFreeportIndonesia E. Widijanto, I. Setiawan, K. Afrizal, M. Stawski, P. Warren and B. Utama, PT Freeport Indonesia, Indonesia
methods and issues G. Fagerlund, SRK Consulting (Canada) Inc., Canada; M. Royle, Schlumberger Ltd., Canada; J. Scibek, SRK Consulting (Canada) Inc., Canada
Slope Stability 2013 | Abstracts
90 Three-dimensionalporepressurepredictionindualphaseconditionsforslopestability assessment E.R. De Sousa, M.J. Fowler, G.E. Swarbrick, Pells Sullivan Meynink, Australia
91 Minedesignforbelowwatertableclaydetritalsmining:MarandooMine,Western Australia D. McInnes, C. Haberfield, Golder Associates Pty Ltd, Australia; P.J.H. de Graaf, Rio Tinto Iron Ore, Australia; C. Colley, Golder Associates Pty Ltd, Australia
92 Thehydro-geotechnicaldecisioncycle–havingminedesignandplanningdecisions made by the right people J.W. Hall, RPS Aquaterra, Australia
93 Thehydrogeologyofamovingcutslopeandrealtimemodellingofgroundwatermovement I. Gray, J. Wood, B. Neels, A. O’Brien, Sigra Pty Ltd, Australia
K. Thoeni, Centre for Geotechnical and Materials Modelling, The University of Newcastle, Australia; C. Lambert, Civil and Natural Resources Engineering, University of Canterbury, New Zealand; A. Giacomini, S.W. Sloan, J.P. Carter, Centre of Excellence for Geotechnical Science and Engineering; and Centre for Geotechnical and Materials Modelling, The University of Newcastle, Australia
96 Coefficientofrestitutionforrigidbodydynamicsmodellingfromonsiteexperimentaldata F.R.P. Basson, R. Humphreys, A. Temmu, Newmont Asia Pacific, Australia
97 SpatialandtemporalaspectsofslopehazardsalongarailroadcorridorintheCanadian Cordillera R. Macciotta, D.M. Cruden, C.D. Martin, N.R. Morgenstern, M. Petrov, Department of Civil and Environmental Engineering, University of Alberta, Canada
98 Earthquakestabilityassessmentforopenpitmineslopes J.C.W. Toh, D.K.E. Green, G.E. Swarbrick, M.J. Fowler, B.E. Estrada, Pells Sullivan Meynink, Australia
99 Seismicstabilityoflargeopenpitslopesandpseudo-staticanalysis B. Damjanac, Varun, L. Lorig, Itasca Consulting Group, Inc., USA
100 Three-dimensionalrockfallmodellingandrockfallprotection–PortHills M.B. Avery, Geovert Ltd, New Zealand; H. Salzmann, Freefall ZT GmbH, Austria; A. Teen, Geovert Global Pte Ltd, Singapore
Slope Stability 2013 | Abstracts
101 VerificationofTrajec3DforuseinrockfallanalysisatNewmontBoddingtonGold C.C. Graf, T. Peryoga, G. McCartney, T. Rees, Newmont Boddington Gold, Australia
H.P. Anderson, Geovert Pty Ltd, New Zealand; A. Teen, Geovert Global PTE, Singapore; H. Salzmann, Freefall Geotechnical Engineering ZTGmbH, Austria
104 RockfallstabilisationofasteepandhighslopeatWestAngelasMineusingpre-tensioned anchored mesh P.J.G. Lopes, T.T. Le, Geovert Pty Ltd, Australia
105 Rockandsoilslopeprotectionusingahighstiffnessgeocompositemeshsystem D. Cheer, Maccaferri S.p.a., Italy; G. Giacchetti, Alpigeo, Italy
106 LandslideriskmanagementinAustralia2013–statusofresourcesavailabletopractitioners A. Leventhal, GHD Geotechnics, Australia; A. Miner, AS Miner Geotechnical, Australia; B. Walker, JK Geotechnics, Australia
107 Designandconstructionofananchoredsoilnailwallclosetomovementsensitivestructures A.K. Kho, Cardno Pty Ltd, Australia; M. McAuley, GHD Pty Ltd, Australia
minimise damage W.W. de Graaf, Mining Engineering Department, University of Pretoria, South Africa; S.J. Etchells, AEL Mining Services, South Africa
110 Measurementsofdynamicsurfacestrainsinducedbyblastingnearahighwallofacoalmine–apreliminaryassessment K.N. Henley, A.T. Spathis, Orica Australia Ltd, Australia
111 Blastingvibrationassessmentofrockslopesandacasestudy K.W.K. Kong, MWH Australia Pty Ltd, Australia
113 Understandingtheblastdamagemechanismsinslopesusingobservationsandnumerical modelling S.J. Etchells, AEL Mining Services, South Africa; E.J. Sellers, JK Tech Pty Ltd, Australia; J. Furtney, Itasca Consulting Group Inc., USA
Keynote addresses
Slope Stability 2013 | Abstracts | 2
Pit slopes in weathered and weak rocks
C.D. Martin University of Alberta, Canada
P.F. Stacey Stacey Mining Geotechnical Ltd., Canada
AbstractThe ‘Guidelines for Open Pit Slope Design’ developed as part of the Large Open Pit (LOP)
project was published in 2009. The guidelines were focused on hard rocks in open pit mines so did not address design issues for pit slopes in materials generally classed as weak rocks. Research currently being undertaken by the LOP sponsors is directed at filling this gap.
Canvassing of the LOP sponsors and their affiliates resulted in identifying pit slope issues in five general categories of weak rocks:
1. Cemented transported sediments.2. Saprolites (residual soils and weathered rocks).3. Leached rocks/soft iron ores (leached, creating a rock with a high void ratio).4. Mudrocks.5. Hydrothermally altered rocks.Establishing the strength of hard rocks is traditionally approached using rock mass
classifications and the Hoek−Brown failure criterion. However, there is ample evidence that these approaches do not capture the strength characteristics and the failure processes evident in weak rocks. In this paper the authors describe some of the processes that should be considered when attempting to establish the strength and failure envelopes input into slope designs for open pits in weak rocks.
Slope Stability 2013 | Abstracts | 3
Numerical analysis, slope design and in situ stress
J. Sjöberg Itasca Consultants AB, Sweden
AbstractThis paper presents a brief review of the history of numerical modelling applied to the design
of rock slopes, with contributions to previous slope stability symposia used to illustrate the development. The related issue of the effect of in situ (or initial) rock stresses on slope stability is also discussed in the paper. The use of numerical modelling has evolved significantly from the first, precarious, steps in the late 1960s. Currently, modelling is a standard tool in almost all slope design work and highly sophisticated models allow simulation of many (if not all) aspects of slope behaviour. Three-dimensional modelling is common and the use of models that allow explicit crack propagation, is slowly emerging. There is, however, still room for improvements within this field. Many of the existing modelling approaches have not been fully validated, mainly due to the problem of obtaining complete geometrical description and properties for all units within a fractured rock mass. The advance in data collection and generation of input data has not kept pace with the improvements in modelling techniques, and rock mechanics problems remains to a large extent data limited. There is a need for more encompassing data collection and monitoring systems for future modelling improvements. An improved characterisation will require extensive collaborative efforts between engineers, geologists, and geophysicists. In the future, a move towards real-time modelling can also be envisioned. This concept has not yet been fully applied in rock mechanics, but there are examples of applications in other engineering and scientific disciplines, such as weather forecasting and physics modelling, and some ideas are presented.
Slope Stability 2013 | Abstracts | 4
Water and slope stability – the application of a new science
G. Beale Schlumberger Water Services, UK
AbstractThe science of pit slope hydrogeology has rapidly gained momentum over the past 15 years
to meet the requirements of larger and deeper mining projects. The advent of new monitoring systems, and particularly the use of grouted-in vibrating wire piezometers, has contributed to a practical understanding of the factors that control the behaviour of water pressure in pit slopes. An expanding global database linking pore pressure with deformation and slope movement is highlighting the role that water pressure plays in slope stability. The talk discusses the importance of water for slope stability, the integration of geotechnical and hydrogeological studies, and the development of a practical approach for project planning, implementation and monitoring.
Slope Stability 2013 | Abstracts | 5
Global slope performance index
T.D. Sullivan Pells Sullivan Meynink; and The University of New South Wales, Australia
AbstractThe evaluation of the performance and risk of excavated slopes is a complex esoteric task.
Slope designers are always faced with gaps and uncertainties and in many cases the conditions as exposed are significantly different to the design predictions. In theory these issues may be addressed with detailed, rigorous investigations, analysis and models. But experience shows that even this approach is not always successful and surprises occur.
The paper presents a simple empirical system for predicting the current and future performance of excavated slopes. The system is the result of decades of experience with the design and evaluation of 100s of slopes excavated for both mining and civil purposes. The examples include a very wide range of slope heights, slope angles, environments and material types. The experience also covers the full spectrum of operational performance, from stable slopes, to complete collapse.
In very simple terms three principal elements contribute to the stability of excavated slopes; intact strength, geological structure and groundwater. The Global Slope Performance Index (GSPI) is based on these three elements divided into five indices. These indices are each rated with a linear numerical scale and then combined into a simple algorithm, the GSPI.
The index has been benchmarked against actual slope performances and demonstrated by statistical analysis, which allows the likelihood of different slope performances and risk to be determined based on the Global Slope Performance Index
Slope Stability 2013 | Abstracts | 6
Data gathering, interpretation, reliability and geotechnical models
J.R.L. Read CSIRO Earth Science and Resource Engineering, Australia
AbstractThe geotechnical model is the cornerstone of open pit design (Read and Stacey, 2009). It must
be in place before the steps of setting up the geotechnical domains, allocating the design sectors and preparing the slope design can commence. The processes that must be followed to construct the model are outlined in this paper. They include recent advances in assessing parameter and model uncertainty, in particular, a modified Bayesian approach that has been developed to estimate the expected value of the measure of reliability. Overall, they form part of a system of reporting confidence in the geotechnical model and matching target levels of geotechnical effort with target levels of confidence in the data at each stage of project development.
Slope Stability 2013 | Abstracts | 7
Excavation control, management of blast damage, and quality control
J.V. Simmons Sherwood Geotechnical and Research Services, Australia
AbstractImplementation of slope design transfers well-intentioned concepts, technical expertise, and
cost commitments to a reality that cannot be fully or reliably predicted. With the uncovering of real geological and operational conditions come observations, actions, and experiences which may mandate changes to design for a multitude of reasons. Within the hierarchy of risk management actions, design is near the highest level of control, and approved design will include acceptance of geological and geotechnical uncertainties. Excavation, blasting, and quality control are aspects of design implementation where intention becomes confronted by reality; choices of action take place within a risk management framework in real time against a background that may be dominated by uncertainties.
Excavation control starts with consideration of survey methods and accuracy limits. Under some conditions, uncertainty in geometry may have a significant influence on outcomes of stability assessment, and this review offers a perspective based on risk management and quality control principles. When inspections are carried out it is necessary not just to identify materials, structure, and groundwater parameters but also to interpret and describe geotechnical behaviour type with respect to an accepted scheme that can guide risk management responses. An example is provided to illustrate the range of rock mass damage associated with different blast designs, with the view that blast damage can be more readily recognised and treated as a special case of excavation control. Quality control is discussed in terms of the gathering of evidence for updating estimates of likelihoods, and may range from simple visual inspection to complex, problem-driven measurements. Some examples are discussed and the overriding requirement to gather, check, and test evidence is emphasised. In conclusion, careful thought is required to resist the distorting aspects of modern communication tools on the timely communication of risk management information.
Geotechnical models
Slope Stability 2013 | Abstracts | 9
Pit slope design in phyllites for the Simandou large open pit project
C. Fietze Golder Associates Africa (Pty) Ltd, South Africa
A. Creighton Rio Tinto, Australia
L.M. Castro Golder Associates Ltd., Canada
R. Hammah Golder Associates, Ghana
AbstractAt the Simandou iron ore project site in Guinea, phyllites with varying degrees of strength
and alteration are prevalent. Their presence makes it difficult to adequately characterise, classify and estimate the strengths of the rock masses. The foliation in the phyllite has low strength, and thus induces anisotropic behaviour. This paper will present information on how these difficult-to-classify rock mass units were treated in the design of the Simandou open pit.
In order to geomechanically characterise the Simandou rock masses, significant attention was paid to the weathering and alteration processes of the phyllite. The strength of the rock masses closely correlated to the degree of alteration and weathering; the most weathered phyllites had the weakest strength.
The strength of the more altered rock mass used for the pit slope design was estimated from a combination of laboratory rock testing and back-analysis. The back-analysis was based on slope instabilities that had occurred on natural slopes in the Simandou area.
The geotechnical risks, most likely to arise, were identified and taken into account in the pit slope design. Since toppling was the most serious of these risks, the paper discusses it in greater detail. Parametric numerical analyses of toppling were performed to evaluate the importance of the variation in the strength and stiffness of the materials and the likely mode of failure, where toppling or shear (rotational-type failure) could develop.
Slope Stability 2013 | Abstracts | 10
Rock mass and structural modelling for the large open pit gold mining project in the Northern Andes: The La Colosa project, Colombia
J. Horner iC consulenten, Austria
J. Weil iC consulenten, Austria
J. Betancourt AngloGold Ashanti Colombia, Colombia
A. Naranjo AngloGold Ashanti Colombia, Colombia
P. Montoya AngloGold Ashanti Colombia, Colombia
J. Sánchez AngloGold Ashanti Colombia, Colombia
AbstractThe La Colosa gold mining project, located in the Central Cordillera of Colombia, wholly
owned and developed by AngloGold Ashanti Colombia, represents the largest gold project in the northern Andes. The project is currently in the pre-feasibility stage (PFS). Rock mass characterisation and the elaboration of a 3D rock mass model and a 3D structural model are required for the geotechnical open pit mine design.
Crucial for the interpretation of structural and geotechnical data is the understanding of the tectonic setting of the area, in order to define major faults and zones of increased fracturing. Prior to rock mass characterisation and 3D modelling, a detailed structural geologic survey was carried out, defining tectonic deformation events and the relation to magmatic and ore-forming activity.
Geologic-geotechnical data from surface mapping as well as from drill core logs of more than 96,000 m of diamond drilling were analysed. In addition, structural data from oriented drillings and from bore hole scanning were evaluated. Review and analysis of drill core data focused on the quality of information acquired during the various stages of drilling and drill core logging. In particular inconsistent data on fracturing and faulting made a detailed review necessary comparing drill core photos with the geologic and geotechnical drill core logs. The result of the re-logging enabled the elaboration of a structural model, the determination of the depth of weathered and fractured material close to surface, as well as the definition of principal fracture zones.
Drill core logging data as well as surface outcrop data were analysed in terms of rock mechanical parameters and were integrated into the existing 3D lithological model. Together with the results from laboratory testing, rock mass types could be defined and modelled in 3D. Seven structural domains were determined using major faults and lithological boundaries as limits, according to the tectonic-structural setting of the deposit.
Slope Stability 2013 | Abstracts | 11
An extensional mechanism of instability and failure in the walls of open pit mines
M.C. Bridges AMC Consultants Pty Ltd, Australia
AbstractEvidence from studies of instability and failures in the walls of open pit mines and cuttings
indicates a predominance of an extensional mechanism, comprising toppling, ravelling and creep-subsidence. This is interpreted to arise from relief and dilation when a pit wall is excavated, removing overburden and lateral confinement of the wall. Evidence does not support sliding and shear or shallow toppling mechanisms of instability or failure.
Slope Stability 2013 | Abstracts | 12
Rapid characterisation of potentially hazardous blocks in open pit mining
M.K. Elmouttie CSIRO Earth Science and Resource Engineering, Australia
G.V. Poropat CSIRO Earth Science and Resource Engineering, Australia
G. Krähenbühl CSIRO Earth Science and Resource Engineering, Australia
P. Dean CSIRO Earth Science and Resource Engineering, Australia
AbstractThe management of open pit mine slope stability analysis can be optimised by using all
available data ranging from qualitative assessment of rock mass properties through to the results of sophisticated computer-based analyses. The choice of approach is typically based on both technical and resource constraints. In this paper we propose a practical method to manage design risks by understanding the potential structure-controlled failure mechanisms of a slope. In particular we emphasise that an understanding of the trustworthiness or level of confidence associated with the stability analysis is essential to manage the rock mass and to determine the appropriate amount of resources required.
The example discussed in this paper involves consideration of the potential formation of kinematically hazardous blocks on a mine highwall or bench face, where it is not clear from the outset what approach is required. The proposed method provides a quick assessment based on the spatial location of structure data and the practical uncertainties resulting from variation of key input data. In this paper, we will present new methods to provide this guidance based on recent advances in the use of digitally mapped structural data, first pass rigid block stability analysis and analysis of the confidence of the stability analysis undertaken.
Slope Stability 2013 | Abstracts | 13
Reliability of strength estimates based on limited laboratory data
M-H. Fillion Lassonde Institute of Mining, University of Toronto, Canada
J. Hadjigeorgiou Lassonde Institute of Mining, University of Toronto, Canada
AbstractIn an open pit mine operation, the quality and quantity of collected geomechanical data can
have significant implications in the design of safe and economically viable slope designs. The selection of representative values of the rock mass properties is not straightforward, given the inherent geological and structural variability within an orebody. Under these circumstances the design of a comprehensive geomechanical sampling program is critical. Such a program, however, has to comply with practical and financial constraints while developing a degree of confidence in the quality of the geomechanical data.
A common target level of confidence in the rock mass properties used in slope design is higher than 80% for an open pit mine at the operations stage. This requires an ongoing maintenance of the geomechanical database and model. In practice, given the perceived high costs of laboratory testing, quite often only a relatively small number of samples are selected for laboratory testing. This leads to a series of questions pertaining to the confidence level that can be assigned to values obtained by testing only a few samples.
This paper investigates the potential of small-sampling theory to provide practical recommendations on the adequacy of a testing program. The geomechanical database of an Anglo American operating open pit mine was reviewed with respect to the strength properties obtained through a series of ISRM suggested testing methods. For the purposes of this investigation the focus was on uniaxial compressive strength (UCS) results but the methodology can be applied to other material properties. In this case study, the mine geological model identified six distinct rock types. Strength values for six different rock domains were analysed using the confidence interval approach. In order to investigate the sequence of testing on the interpretation of results, statistical analyses were also performed by randomly interchanging the order of test results for each rock domain. The results showed that even if the number of specimens tested is higher than the minimum proposed by the International Society for Rock Mechanics (ISRM) suggested methods, the sample size was too small to obtain a reliable strength value for most of the rock domains. Furthermore, the results showed that the minimum sample size obtained using the confidence interval approach is significantly influenced by the test results sequence used for the analyses. Based on the results of this study, there is a demonstrated need for a method to determine the minimum sample size while minimising the influence of the testing sequence.
Slope Stability 2013 | Abstracts | 14
Interpreting local critical orientations of structural weakness in relation to stress and dilatancy in rock slopes
J.V. Smith School of Civil, Environmental and Chemical Engineering, RMIT University, Australia
AbstractThe orientation of structural weaknesses, such as faults, joints, bedding and foliation, is a
major influence on the stability of rock slopes. In the unloaded parts of benches, the critical orientation of structures is typically considered with respect to gravity. In the toe of each bench and the zone of rock behind the benches the critical orientations must be considered with respect to the local stress trajectory. In this zone the maximum principal compressive stress (σ1) is approximately parallel to the slope, in a two dimensional cross-section. This principal stress orientation approximates the inter-ramp slope angle for a series of benches with local steepening of the trajectory behind the lower part of each bench and local flattening behind the top part of each bench. The critical structures will be those with orientations favourable to slip with respect to the local σ1 trajectory. The orientation of surfaces favourable to slip is also related to the friction angle and dilatancy of a material.
Materials which undergo no volume change during deformation typically slip on surfaces at 45° to σ1 . Materials undergoing volume increase during deformation slip on surfaces at lower angles. This can be observed in conjugate pairs of structures where the slip occurs simultaneously on ‘mirror image’ structures. The angle between conjugate structures in rocks is typically around 60°, that is, each structure is inclined 30° to σ1 . Experiments and field observations have shown that this angle decreases at lower confinement and increases at higher confinement.
Based on these relationships, a slope of 50° would have σ1 inclined at approximately 50° (with local variations) and the conjugate critical structures would therefore be oriented at 20 and 80° out of the slope. The low-angle structure would have a resolved shear displacement of sliding out of the slope. The high angle structure would have the opposite shear sense, that is, the block behind the slope moving down relative to the block nearer the slope face. Movement on the high-angle structures can appear to be a toppling failure. At the toe of the overall slope, where stresses are at their most concentrated, σ1 will progressively flatten to horizontal as it goes under the pit floor. In the zone of greatest stress concentration, the σ1 trajectory will approximate half the slope angle, depending on factors including the in situ stress ratio. At this location, σ1 would be, for example, inclined at approximately 25° and the conjugate critical structures would be oriented at approximately 5° into the slope and 55° out of the slope. Movement on the low angle structures can be upward into the pit and may appear to be heave in the pit floor. Movement on the high-angle structures can also appear to be heave in the pit floor.
Rock slopes which contain structural weakness oriented in one or both of the local critical orientations will undergo plastic yield at a lower threshold than other rock masses. The susceptibility of structures to this effect can be assessed from a stereograph using the…
Slope Stability 2013 | Abstracts | 15
Combining field methods and numerical modelling to address challenges in characterising discontinuity persistence and intact rock bridges in large open pit slopes
Z. Tuckey Coffey Mining Pty Ltd, Australia
D. Stead Department of Earth Sciences, Simon Fraser University, Canada
E. Eberhardt Department of Earth and Ocean Sciences, University of British Columbia, Canada
AbstractConfidence in stability assessments of large rock slopes may be improved by greater
understanding the persistence of adverse discontinuities, and the proportion and location of intact rock bridge content within the slope. This paper presents a discussion of the challenges and uncertainty in characterising discontinuity persistence and intact rock bridges, with reference to results from field investigations of open pit slopes at three mines using digital photogrammetry, ground-based LiDAR, and modified 2D window mapping methods. A conceptual numerical model is then devised, where a distinct element numerical code was applied to investigate the influence of rock bridges on brittle rock mass failure and dilation in a model large open pit slope.
Distinction between co-planar or out-of-plane intact rock bridges, and larger ‘rock mass bridges’ between more persistent discontinuities is considered necessary and the authors suggest that a fracture network engineering approach tailored to large open pits may be helpful for their characterisation. With modified trace mapping procedures, intact rock bridges may be quantified in terms of an intensity parameter R21 that describes the total length of inferred rock bridge traces per unit area within a mapping window. An analogous blast-induced damage intensity factor B21 is also introduced, that describes the total length of blast-induced fracture traces per unit area in a mapping window. For numerical models, a damage intensity parameter D21 is applied, which quantifies the intensity of fracturing that develops inside a modelled slope.
Slope Stability 2013 | Abstracts | 16
Discussion on how to classify and estimate strength of weak rock masses
L.M. Castro Golder Associates Ltd., Canada
J. Carvalho Golder Associates Ltd., Canada
G. Sá Vale, Brazil
AbstractWeak rocks can be found in many mines around the world, such as the weathered (saprolite/
saprock) rocks in tropical areas, the (argillic) altered rocks in the Andes and several gold mines in Nevada, and the soft iron ore deposits in Brazil and Africa. However, it is difficult to classify these materials from drilling core and obtain representative strength for these weak rock masses. This paper discusses the rock mass classification and proposes a transition function for estimating their strengths.
Current application of the rock mass rating (RMR) – Bieniawski classification system and its subsequent input into the Hoek–Brown strength criterion yields low strength parameters that do not represent high stable slopes excavated within weak rock masses, as observed in many mine operations and road cuts.
This paper presents some modifications to the RMR76 system, which somewhat takes into account the Robertson (1988) proposed classification system for weak rock masses, by allowing the collection of ratings for RQD and joint condition to obtain higher RMR values for the upper portion of the R1 (i.e. R1+ or R1/R2) and R2 category rock masses that would be greater than the current minimum value of 18 for dry slopes. The RMR classification should not be applied to R0 type materials (UCS<1 MPa), as they should be treated as soil.
It is recognised that at the low end of the rock quality scale, in the transition from inter-block shear failure towards a more matrix controlled rock mass behaviour, a gradual change in the strength curve can be created by considering the reduction in the cohesion component. For the estimation of the weak rock mass strength, a low-end transition Hoek–Brown relationship originally proposed by Carvalho et al. (2007) has been calibrated with additional data and considering the strength range from R1 to R2 materials.
Sá (2010) carried out laboratory strength tests and back-analysis of failed slopes for the N4E open pit iron mine in the Vale’s Carajás Mineral Complex, located in the north of Brazil. The calibrated strength parameters were used to assist in defining the lower strength limit, where this transition function should not be applied. Examples for other mines are also included, where weathered/altered rocks exist and were compared with strength parameters estimated from this low-end transition relation.
Slope Stability 2013 | Abstracts | 17
Structural data bias in the digital age
M.J. Fowler Pells Sullivan Meynink, Australia
AbstractThis paper presents a description of data bias associated with both conventional and digital
mapping of rock mass discontinuities. Digital mapping of rock mass discontinuities is now commonplace with, for instance, borehole imaging, LiDAR and photogrammetry becoming standard tools for geotechnical investigations.
Rock mass discontinuities are a major control on the design of hard rock slopes and underground openings. Understanding the inherent bias of different sampling methods is an important aspect of building reliable engineering geological models.
Slope Stability 2013 | Abstracts | 18
Bench berm design using probabilistic key block analysis
E. Hormazabal SRK Consulting (Chile) S.A., Chile
AbstractIn operational open pit mines, large rock surfaces are exposed daily and hundreds or
thousands of new discontinuities are exposed, all of which may results in the formation of unstable key blocks and wedges. It is impractical to attempt to map each discontinuity and carry out a stability analysis by the traditional kinematic analysis and wedge/planar failure analysis for each discontinuity mapped. The approach presented in this paper is to design the bench berm configuration in such a manner that sufficient key blocks and wedges will be analysed by probabilistic methods so that an acceptable level of safety is achieved. Geotechnical engineers therefore require a design tool which will allow them to evaluate the type and frequency of key blocks that may be formed and the effect of decreasing the bench angle or increasing the berm width on the probability of failure of the key blocks.
This paper describes a computer program, SBlock in which a probabilistic method is applied to determine the potential key block dimensions, the back break and the berm width for given acceptability criteria. Also, two case histories of operational open pit mines are presented to validate the methodology and calibrate the results.
It is concluded that a probabilistic approach is suitable for the evaluation and design of the bench berm configuration in situations where a large numbers of discontinuities are exposed in the operational open pit benches.
Slope Stability 2013 | Abstracts | 19
Ongoing research into anisotropic rock masses using numerical modelling
K.G. Mercer Australian Centre for Geomechanics, The University of Western Australia, Australia
AbstractThis paper details results from the ongoing numerical modelling research into the shear
strength characteristics of planar anisotropic rock masses such as those found in the Pilbara region of Western Australia. Numerical simulations using the distinct element code UDEC were used to model different weathered anisotropic rock formations such as shales and Banded Ironstone Formations (BIFs).
These simulations confirmed the overall shear strength reduction due to sliding on planar discontinuities at angles sub-parallel to bedding and better quantified the difference between the planar anisotropic transition models (ATMs) for shale and BIF. However, the modelling revealed a zone of upslope shear strength reduction (USSR) which can occur at positive angles of anisotropy (AoA) between 40 to 90° under certain rock mass configurations. This zone was identified but not previously quantified in earlier studies.
The magnitude of the shear strength reduction is dependent on the tensile strength of the intact rock as well as bedding parting spacings. The USSR has significant implications especially in relation to the effect on the stability of slopes having particular configurations of anisotropic rocks. The current ALM1 and ALM2 do not take the USSR into account and therefore can potentially overestimates the shear strength of the rock mass in this range of AoA. Consequently a new ALM (ALM3) has been developed which does take the USSR into account. Until the ALM3 is coded into commercial software and the new ALM3 parameters more rigorously defined, care should be exercised when assessing the stability of slopes having these geological formations and geometry.
Slope Stability 2013 | Abstracts | 20
Geochemistry and geotechnical models – a case study from the proposed Kempfield Silver Project, Bathurst, New South Wales
H. Baxter Pells Sullivan Meynink, Australia
T. Rutherford Pells Sullivan Meynink, Australia
R. Bertuzzi Pells Sullivan Meynink, Australia
AbstractThis paper presents a case study on the proposed Kempfield Silver Project where geochemistry
was used to define sub-surface fault structure orientation. The Kempfield site is located within the Hill End Trough along the eastern margin of the Lachlan Fold Belt. Surface outcrop is sparse with mapping mostly limited to lithology. However, similarities in the alteration of the lithologies limited their use in correlating faults. Geochemical assays of chip samples were made for over 35 minerals/elements, including aluminium, titanium, potassium, calcium and iron. Using Vulcan to view boreholes in 3D, the amounts of each element was assessed for correlations that may define changes in lithology, alteration or the presence of structures. Iron grades (Fe) proved the most favourable for the identification of structures at depth, with a distinct correlation of lithology with >5% Fe on the hanging wall of faults and <5% on the footwalls. The fault dips indicated by the geochemical assessment were commensurate with fault orientations from oriented core. This information was then factored into the geotechnical model and used as part of the slope stability analysis.
Slope Stability 2013 | Abstracts | 21
Combined use of traditional core logging and televiewer imaging for practical geotechnical data collection
X.P. Gwynn SRK Consulting (UK) Ltd, UK
M.C. Brown SRK Consulting (UK) Ltd, UK
P.J. Mohr SRK Consulting (UK) Ltd, UK
AbstractAcoustic and optical televiewers are becoming routinely used to capture structural
geotechnical data for use in pit slope and underground design. They provide rapid and accurate high resolution oriented images of the borehole walls and can be used as a replacement for manual core orientation techniques, with the picking of structures being left to the televiewer operator who then provide the data to the geotechnical engineers. SRK UK Ltd. has developed an approach where the raw acoustic televiewer logs are used in conjunction with manual rock mass logging of the core. This hybrid logging method allows for the detailed description of each open feature whilst making use of the accurate structural orientation measurements obtained from the televiewer data. The depth correlated structural logging data is subsequently used to populate a rock mass log, automatically producing rock mass classification values. This rapidly reduces the time required for geotechnical logging; thus reduces field time requirements of the consultant and potentially reduces cost to the client. The paper covers the current field methodology, required post processing of the logged data and discusses advantages and disadvantages of using this hybrid method. A case study from Scandinavia is also presented.
Slope Stability 2013 | Abstracts | 22
Experimental and numerical assessment of shear surface damage using 3D point clouds
S. Karekal CSIRO Earth Science and Resource Engineering, Australia
G.V. Poropat CSIRO Earth Science and Resource Engineering, Australia
H. Guo CSIRO Earth Science and Resource Engineering, Australia
AbstractThis paper describes modelling of shearing of rock joint surfaces using 3D point clouds
generated using photogrammetry. High resolution 3D images of discontinuity surfaces were created before and after shearing. The surface damage due to shearing of joint surfaces was assessed using image processing by comparing the 3D images of undamaged surfaces with those of damaged surfaces. The shear surfaces were concrete replicas of natural surfaces. The damage due to shearing was estimated using numerical modelling in which comparison was made between the concrete surfaces before and after the shear test. It was found that the modelling results were fairly well correlated with the observed surface damage, thus validating the numerical models. The digitised surfaces could also be used to predict anisotropic shear strength and damage of the asperities by numerically shearing the joint surfaces at various directions.
Slope Stability 2013 | Abstracts | 23
The determination of joint roughness coefficient using three-dimensional models for slope stability analysis
D.H. Kim School of Engineering, Griffith University, Australia
I. Gratchev School of Engineering, Griffith University, Australia
G.V. Poropat CSIRO Earth Science and Resource Engineering, Australia
AbstractJoint roughness coefficient (JRC) is one of the important parameters to determine shear
strength of joints. JRC values are generally measured using profile gauges and estimated by comparing the surface profiles with typical roughness profiles. Therefore, the values can be subjective and vary depending on personal experience of an engineer. Digital photogrammetry methods provide 3D models based on high resolution digital images, and thus JRC values can be more objectively estimated from photogrammetry analysis using linear profile data.
This paper seeks to investigate the feasibility of using the photogrammetry method to obtain JRC values. Photogrammetry surveys were performed at several slope sites, and JRC values were estimated using 3D images. To investigate the effect of resolution of digital images, the JRC values were first obtained using different distances between the slope and camera, and then compared with the roughness profiles which were manually measured by means of a Barton’s comb. A computer analysis using the distinct element code UDEC was also performed to better understand the effect of JRC on the stability of slopes.
Slope Stability 2013 | Abstracts | 24
Geotechnical and geological model applied to crushing processes in open pit mines
P. Peña Ingeniería de Rocas Ltda., Chile
R. Fuenzalida TECK Carmen de Andacollo, Chile
R. Villarroel Ingeniería de Rocas Ltda., Chile
P. Merino Ingeniería de Rocas Ltda., Chile
M. Tapia TECK Carmen de Andacollo, Chile
P. Casanova Geoatacama, Chile
AbstractThe geotechnical model for pit stability in Carmen de Andacollo (CDA) deposit does not offer
a good interpretation to predict or explain the rock behaviour in the crushing process. This work proposes a modification to the database analysis and geotechnical characterisation to create a three-dimensional model that can predict and explain the rock behaviour in this process. Two lines where followed to develop this work: 1) define particle size results after blasting, according to the geological conditions; and 2) define the intact rock behaviour in the crushing.
Considering the geotechnical tests to characterise the intact rock, the tensile test (Brazilian test) is the one that best correlates with the crushing process. This test breaks the rock through tensile stress, however at the moment of this study, there was scarcity of this type of test and it had a low representativeness in the deposit. Hence, the point load test (PLT) was selected because it was the most representative parameter available; at a low cost and in addition, it is an indirect measurement of the tensile strength.
The following defined the particle size characteristics of the rock mass after blasting: mesh through which 50% P(50) and 80% P(80) of the blasted material passed and the percentage of pieces smaller than 67 mm, between 67–100 and >100 mm. This information has different meshes and was assessed in function of lithology, geotechnical unit and mineral zone. This analysis allowed choosing four parameters to define the rock mass crushability. Point load strength PLT(IS(50)) corresponds to a strength index where two tapered points are buried in the rock specimen opening it by tensile stress. The purpose of using PLT is to use the trends generated with this test to assess the general rock’s stress strength.
Mineral zone is relevant in the behaviour of the particle size and strength of the intact rock as it establishes the level of weathering or the environmental effect on the rock. Rock quality designation (RQD) is an indirect indicator of in situ particle size of the rock mass as it measures the percentage of diamond drill cores larger than 10 cm per drilled section. In this case, RQD was the best-distributed geotechnical parameter available for the deposit. Hydrothermal alteration characteristics complement the information provided by the mineral zone. That is how the siliceous alterations create a significant increase in tensile strength and in the rock’s…
Slope Stability 2013 | Abstracts | 25
Maximising geotechnical data and characterisation of critical units through targeted field work
A.J. Phillips Coffey Mining Pty Ltd, Australia
H.F. Wilson Coffey Mining Pty Ltd, Australia
AbstractIdentification and investigation of weak geological units and structures is an important
component of a slope design. Such units and structures are highly prone to weathering and typically exhibit lower shear strength than the surrounding rock mass. These units are inherently problematic to obtain quality geotechnical data from due to their fragile nature and often limited frequency. It is therefore essential that a data collection campaign is designed and implemented with the view of collecting maximum quality and representative data from these units. Samples with minimised disturbance from diamond drill core provide a valuable insight into the in situ ground conditions of these units. This method of data collection requires good quality drilling and early identification of weaker units to maximise recovery. Careful handling, correct sampling and transport procedures to enhance preservation of the core until geotechnical laboratory test work can be undertaken are equally essential. It should be ensured that samples are preserved in their in situ conditions prior to arrival at the testing laboratory. Consideration needs to be given to communication between all personnel, early identification of critical weak units, timing of logging and sampling and sample transportation and storage. This paper aims to provide a methodology for sampling of such materials, building on the knowledge of the current standards and best practice benchmarked with other industries. The ultimate result is the ability to collect and preserve a higher quantity and quality of samples of weak material critical to slope stability. With increased sampling from weaker units, it is possible to rely more on results of laboratory testing and reduce reliance on empirical methods for shear strength characterisation. This provides increased confidence in the geotechnical model and ultimately slope design.
Slope Stability 2013 | Abstracts | 26
Structural geology modelling: a summary on data integrity and modelling methods
K.M. Rees Golder Associates Pty Ltd, Australia
J. Graaf Golder Associates Pty Ltd, Australia
AbstractThe creation of a structural geology model greatly improves the geotechnical understanding
of a deposit by giving meaning to the thousands of defect measurements collected. Structural geology models are all about geometry; geometry of the various rock packages and geometry of the overriding structural framework. Geotechnical models on the other hand deal in the details; the statistical defect set orientations, the spacing between the defects and their infill and surface characteristics. In order to get an overall picture of the rock mass, the geotechnical model needs to be assessed in association with the structural geology model and vice versa. Structural geology models incorporate a vast array of data types, including drillhole, televiewer, conventional geological mapping, photogrammetric geological mapping, etc., but how accurate and complete is all of this data? The integration of multiple data types into a structural geology model can be fraught with complications. Varying levels of accuracy occur between different datasets and these variants need to be assessed prior to structural geology modelling. Where conflict exists between multiple data types, the most accurate data should be used, thus it is important to understand data accuracy. Drillhole data for example can be affected by inaccurate orientation marks and survey pickups, leading to inaccurate structural measurements. Furthermore, the spacing and orientation of drillholes often does not provide a representative sample of the rock mass as the drill design is generally tailored to the geometry of the ore body for resource modelling. These factors need to be understood when using the data to create a structural geology model. While orientated drillhole data provides a good basis, integrating other data types such as geological mapping provides for a more robust model, however conventional geological modelling comes with its own set of issues.
Advances in data collection techniques can enable many of the issues associated with poor data quality to be overcome. Televiewer data can be used to validate drill core logging data, while photogrammetry techniques can enable accurate digital geological maps to be created. However, regardless of the method employed, it is paramount that adequately trained personal carry out the mapping to ensure high quality data. The purpose of this paper is to discuss the quality of data used in structural geology modelling and present reasons for applying new technologies to your mining operation or resource assessment.
Slope Stability 2013 | Abstracts | 27
A statistical approach to account for elevated levels of uncertainty during geotechnical design
R.D.H. Thomas Coffey Mining Pty Ltd, Australia
AbstractUncertainty in geotechnical engineering results from the inherent variability of natural
materials, and the challenges engineers and geologists have in correctly assessing them. Geotechnical design at the definitive feasibility study (DFS) stage should be based on a geotechnical model with target levels of confidence of ideally between 50 and 75%. Due to various reasons such as budgetary constraints for ground investigation or changes to the resource model affecting mine design, a higher degree of data uncertainty can exist in one or many of the model inputs. This can be accounted for by selection of conservative design values, but where probabilistic design is desired further uncertainty can be induced by estimating population characteristics, for instance by adopting coefficients of variation from published literature, e.g. Harr (1987) and Kim (2005).
This paper presents a case study for a DFS level open pit slope design for a gold project in West Africa. The geological, structural and hydrogeological models were suitably defined, however limited geotechnical drillhole data was available for some units. The limited data sets hindered rock mass characterisation and derivation of design values (and distributions) for subsequent slope stability modelling, resulting in elevated levels of uncertainty. The author was faced with the prospect of either accepting the uncertainty and accounting for the small populations by choosing lower bound values and assumed distributions, or relying on regional data from experience of working with the encountered units elswhere. In an effort to ensure the most relevant, deposit specific data was used, the author sought to supplement the limited data sets with additional drillcore data from elsewhere within the project area.
The challenge the author faced was to justify combining data that would conventionally be considered separately. A number of statistical tests were used to demonstrate the validity of combining the different populations of drillcore data. A suite of logged and derived parameters were tested. The results of the statistical analyses and the effect of combining drillcore data populations on the resultant level of uncertainty and ultimate pit slope design are presented.
Slope Stability 2013 | Abstracts | 28
Preliminary review of the geotechnical characteristics and shear strength estimates of small scale anisotropic waveform formations of the Pilbara, Western Australia
S. Tokimoto School of Civil and Resource Engineering, The University of Western Australia, Australia
K.G. Mercer Australian Centre for Geomechanics, The University of Western Australia, Australia
AbstractAnisotropic rock masses such as the Hamersley Group found within the Pilbara region of
Western Australia commonly exhibit pervasive folding in wavelengths ranging from several centimetres to large regional folding with wavelengths of up to several kilometres. All folding influences the stability of open pit slopes however the influence of relatively small scale folding is particularly difficult to account for in limit equilibrium slope stability analysis. In addition, existing research work on assessing the shear strength of anisotropic rock masses has thus far, only considered the effect of planar discontinuities.
Using data from published literature, the paper will provide a general over view of the geological and geotechnical characteristics of formations within the Pilbara region of Western Australia where waveform formations are typically found. The paper will then go on to review the scale at which the waveform folding of bedding is likely to have the greatest impact on the shear strength of anisotropic rock masses and how these different scales can be modelled when assessing the stability of pit slopes. Finally the paper will present some preliminary results of numerical modelling studies of the shear strength characteristics of small scale waveform formations using two commonly occurring rock types found in the Pilbara region.
Slope Stability 2013 | Abstracts | 29
Dissection of a pit – case study
A.J. Troy Terra Firma Australia Pty Ltd, Australia
AbstractGiven that ‘Mother Nature’ is the ultimate arbiter in terms of actual material strengths
and appropriate pit design, a progressive slope failure experienced at Mine A has highlighted opportunities to improve geotechnical awareness and balanced risk reduction. The dissection of a pit approach uses the unwelcome failure to examine five contributing geotechnical factors, their associated challenges and overall assumptions previously made. The resulting back analysis and focussed material strength re-interpretation highlights the need for regular and ongoing performance reconciliation to identify and resolve inconsistencies within the geotechnical model. With this in mind, it is hoped that elements from the findings will be considered during successive ground investigations, for deposits in related environments.
Remediation
Slope Stability 2013 | Abstracts | 31
A strategic approach to the design and implementation of an effective mine dewatering system
M. Bester Anglo American Kumba Iron Ore, South Africa
E. Nel Anglo American Kumba Iron Ore, South Africa
G.M. Mc Gavigan Anglo American Kumba Iron Ore, South Africa
AbstractIn order to reduce business and safety risk at Anglo American Kumba Iron Ore mining
operations, it is imperative that groundwater is strategically managed to ensure dry mining conditions and depressurised slopes whilst ensuring maximum effective usage of the abstracted water and managing the potential environmental impacts. Hydrogeological input into slope design is required in order to ensure safe mine production and minimisation of costs. A structured approach according to engineering design principles is suggested for the design and implementation of an effective and efficient mine dewatering system. Comprehensive data collection and site characterisation, conceptual and numerical groundwater flow modelling as well as dewatering simulations are required to accurately determine the dewatering system requirements. Subsequent to implementation, a comprehensive monitoring program is put in place in order to optimise the dewatering system and effectively manage the environmental impact. The implementation phase of an effective dewatering strategy at Sishen and Kolomela Mines are discussed as case studies.
Slope Stability 2013 | Abstracts | 32
Water management for slope stabilisation – an example from Peru
C. Pérez Schlumberger Water Services, Peru
V. Pérez Minera Yanacocha S.R.L, Peru
G. Beale Schlumberger Water Services, UK
D. Ríos Minera Yanacocha S.R.L, Peru
F. Soto Minera Yanacocha S.R.L, Peru
AbstractPeru is one of the world’s leading mining countries and includes a number of large open pits
such as Antamina, Toquepala and Yanacocha. The Yanacocha operation comprises six large pits including El Tapado where mining has been ongoing since 1999. Instability of the north wall of the El Tapado pit occurred as the slope was mined down. Initial site investigations identified high water pressures in the permeable silica alunite material behind the slope and also in strongly altered propylitic clays at shallower levels within the slope.
Minera Yanacocha created a multi-disciplinary team of mining engineers, geotechnical and hydrogeological staff to develop a mitigation plan to allow mining of the slope to continue. The failure main surface was identified at the silica alunite contact within the overlying clays using piezometer and inclinometer installations. The silica alunite had a permeability range from 10-3 to 10-6 m/s and it was possible to install pumping wells to reduce the water pressures. The overlying propilitic clay had a much lower permeability (10-7 to 10-8 m/s) and the plan was to depressurise the material using a combination of surface water controls, under-drainage by pumping from the silica alunite and horizontal drain holes. The first stage of the program was to install a joint monitoring network which could measure the both the pore pressure and slope movement response to the initial dewatering wells in the silica alunite. The second stage was to install the surface water controls to minimise ongoing infiltration and recharge to the clay units during the wet season. The third stage was the horizontal drain hole program to increase the rate of depressurisation of the propyllitic clays and to evaluate the coupled hydromechanical response associated with the ongoing excavation of the pit wall. This paper explains the joint methodology performed by the project team to stabilise the slope and allow mining to near the full planned depth of the pit.
Slope Stability 2013 | Abstracts | 33
Cockatoo Island stage 3: seawall failure and remediation
P.K. Wong Coffey Geotechnics Pty Ltd, Australia
P. Petropulos Coffey Mining Pty Ltd, Australia
AbstractThe hematite mining operation at Cockatoo Island, Western Australia, required the
construction of a 13 m high, composite earth and rockfill seawall to exclude 10 m tides from the Indian Ocean. The Stage 3 seawall is underlain by up to 30 m of soft, low permeability coralline sediments which are in turn underlain by stronger and higher permeability marine sediments and hematite scree layers. During initial construction, a 140 m section of the seawall failed when a height of 8.7 m was reached.
This paper describes the post failure investigation and analysis results, and the remedial works which were successfully completed. The investigation results indicated the basal drainage characteristics of the coralline sediments to be variable along the length of the seawall. At the location of the failure, basal drainage was very low and this was considered to be a major contributing factor to the failure coupled with rapid construction of the embankment. Instrumentation and monitoring prior to the failure was limited, partly due to difficulties associated with high tidal fluctuations. In contrast, the remedial work was carried out successfully with a significantly improved instrumentation and monitoring system, including inclinometers, extensometers, piezometers, settlement plates, survey prisms and total pressure cells. A rigorous review and approval process was developed in conjunction with the client, Cockatoo Mining, using an observational method to assess the risk of instability prior to placing each additional embankment layer.
The degree of client involvement and the collaborative approach adopted in relation to the observational method, approvals, data transfer, and joint management for the remedial work is extremely rare on most mines. The successful completion of the remedial work demonstrated that such a collaborative approach is a key ingredient to the successful completion of high risk projects in complex ground conditions.
Slope Stability 2013 | Abstracts | 34
Case history: deep-seated slope failure in weak rocks, El Tapado pit north wall, Yanacocha operation
G.A. Becerra Abregu Minera Yanacocha S.R.L., Peru
E. Valencia Jeri Minera Yanacocha S.R.L, Peru
E. Garcia Minera Yanacocha S.R.L., Peru
P. Yuan Golder Associates Inc., USA
T. Byers Newmont Mining Corporation, USA
AbstractThe Yanacocha Operation is an open pit gold mining operation in the Andes Mountains of
Northern Peru. Since 1993, mining at Yanacocha has occurred in eight large pits, and several smaller pits. Mineralisation typically occurs in hydrothermally-altered volcanic rocks. Weak rocks at Yanacocha include argillically- and propylitically-altered volcanic rock masses, which are often in sharp contact with higher-strength rock masses with silica and silica-alunite alteration. Although mineralisation generally occurs in the silica-altered rock masses, pit slopes are developed in part in the weaker rocks.
In October–November 2010, a deep-seated instability was identified in the north and northeast walls of the El Tapado (ET) Pit. The implications of the instability were substantial, in that it put up to 400,000 ounces of gold at risk in the ET Pit; and affected the planned production schedule for the adjacent El Tapado Oeste (ETO) Pit, as much of the waste from ETO was to be placed as backfill in the ET Pit. This instability also possessed the potential to propagate beyond the pit crest, and impact the stability of a large waste dump and a main haul road located just outside the pit limit.
Mining in the area of the north wall was discontinued between December 2010 and July 2011 to allow for:
• Geotechnical, geological, and hydrogeological characterisation.• Development of alternate mine plans.• Evaluation of design changes and development options.• Stability analyses.• Assessment of slope displacement experience.• Slope depressurisation.Mining resumed in July 2011, subject to slope displacement monitoring, and a process of
continuous input and review from the site Geotechnical, Hydrogeological, Planning, and Mine Operations groups; and a group of external geotechnical and hydrogeological professionals. The ET Pit was completed successfully in July 2012.
This case history summarises the conditions that contributed to the instability in the ET North…
Slope Stability 2013 | Abstracts | 35
Pit slope depressurisation investigation for an open cut iron ore mine in the Pilbara
A. Dodman Schlumberger Water Services, Australia
G. Beale Schlumberger Water Services, UK
J. Rodriguez Schlumberger Water Services, Australia
A. Cottrell BHP Billiton, Australia
J. Youngs BHP Billiton, Australia
AbstractIron ore mining operations in the Pilbara region of Western Australia are currently undergoing
unprecedented growth. Expansion of active open cut mines and development of new deposits below the pre-mining water table, present significant challenges in terms of general mine dewatering and pit slope depressurisation. Studies to characterise pore pressure behaviour have become a key component of the mining cycle. Pore pressure inputs to geotechnical slope stability assessments and timely implementation of mine drainage is essential to optimise slope design, performance and safety.
This paper presents a case study of a staged hydrogeological study for a large highwall at an active iron ore mine in the Pilbara. The primary objective was to characterise pore pressures, provide input to slope design studies and support management of pit slope depressurisation, ahead of an aggressive pushback. The bulk stratigraphy is structurally complex, defined by alternating banded iron formation (BIF) and shale macro-band sequences. Key geotechnical issues include a number of fault structures identified behind the final pit wall which may require a high level of advanced depressurisation, saturated low permeability footwall shale units and potential hydraulic connectivity between the local orebody groundwater system and a regional dolomite aquifer.
Installed vibrating wire piezometers (VWPs) show a strong response to pumping within the mineralised BIF. In contrast, high pore pressures prevail within the deep shale units. The study demonstrates the importance of integration between hydrogeological and geotechnical programs to provide adequate planning for the design and implementation of dewatering and slope depressurisation systems, and presents key learning outcomes for similar environments.
Slope Stability 2013 | Abstracts | 36
Approach to groundwater and pore water pressure modelling for different geotechnical conditions in open pit slope stability analysis
H. El-Idrysy SRK Consulting (UK) Ltd, UK
AbstractThis paper presents two feasibility case studies related to groundwater modelling for pit slope
stability studies at a diamond mine and a gold mine. While both open pit mine projects had a target final pit depth of about 450 m the impacts of groundwater conditions on the slope stability analyses are very different. The former required very detailed analysis and simulation of pore water pressure whilst at the gold mine, both groundwater flow and pore water pressure had limited impact on the slope stability assessment. The two case studies demonstrate that pore water pressure does not always significantly influence the stability of the pit slopes and that it is essential to identify the key controlling factors for slope stability before embarking on detailed modelling of pore water distribution. However, when pore water pressure and groundwater flow are identified as controlling factors due to geotechnical setting, extensive numerical modelling of groundwater flow is required to optimise a dewatering/depressurisation system that achieves the required Factor of Safety (FS) from pit slope stability analyses. A fully integrated numerical modelling analysis of pore water pressure and geotechnical slope stability is an intensive, iterative exercise but the result of such work is very rewarding in terms of optimising pit slope angles.
Slope Stability 2013 | Abstracts | 37
A case study on actual water pressure measurements at an open pit excavated in strong, tight rock and the implications for slope design
M. Rougier Golder Associates Ltd., Canada
L.M. Castro Golder Associates Ltd., Canada
D. Birchall Barrick Gold, Canada
AbstractPrecedent experience is that deep open pit slopes in strong, tight rock masses with high
groundwater pressure will not exhibit rock mass failure. The phenomenon is not disputed. It is noted that simple limit equilibrium or finite element slope stability models, often relied upon in mine design and feasibility assessment, can indicate the contrary for high groundwater pressure conditions. In part this is because case history examples on actual groundwater pressure information from this type of open pit are limited. Consequently, over-conservative groundwater conditions can on occasion been assumed for stability analysis purposes.
This paper presents a case study of the results of actual measurements of pore water pressure during pit development using vibrating wire piezometers. They were taken for the purpose of addressing risk management concerns over non-conservative stability analysis results for pit deepening and expansion of the Williams open pit at Barrick Gold’s Hemlo Operations. The property is situated on the north shore of Lake Superior near Marathon, Ontario, Canada, in an area of moderate hydraulic recharge.
The actual drawdown cone was found to be tight to the pit shell at depth, yet broader than expected near−surface. This may have been due to structural features and the interpreted effect of blast damage or the combination of slow excavation and moderate recharge. Site-specific observations are presented in terms of their implications for future slope design at Hemlo and in terms of the groundwater aspect of slope stability modelling in tight rock in general, particularly where limited information is available.
Uncertainty in design
Slope Stability 2013 | Abstracts | 39
An application of a reliability based method to evaluate open pit slope stability
M. Valerio Golder Associates Ltd., Canada
C. Clayton Golder Associates Ltd., Canada
S. D’Ambra Golder Associates Ltd., Canada
C. Yan Golder Associates Ltd., Canada
AbstractThe stability of open pit rock slopes is commonly assessed using deterministic methods. A
single value for the Factor of Safety of the slope is calculated, and is assumed to represent the overall stability of the slope. A limitation of the deterministic approach is that it does not account for the natural variability of the input parameters or the uncertainty caused by sampling. The uncertainty and variability of input parameters such as frictional strength, cohesive strength, and discontinuity orientations are often accounted for by selecting values that incorporate conservatism based on limited laboratory testing or other data collection methods. The confidence in the Factor of Safety calculated using deterministic analyses remains a matter of engineering and experiential judgment.
Reliability based methods, now adopted by many practitioners, overcome some of the limitations of deterministic methods by incorporating the natural variability of key input parameters into the calculation methods. If the natural variability is included, then a range of Factors of Safety can be calculated for the various combinations of the input variables. This range represents the probability density function of the continuous distribution of Factors of Safety, from minimum to maximum values. The cumulative distribution of values can then be used to quantitatively describe the likelihood of achieving a certain Factor of Safety. Understanding the distribution of Factors of Safety, and the reliability of the results, provides a method to make reliability based decisions.
This paper presents a feasibility level study undertaken for Diavik Diamond Mines Inc. using point estimation methods in combination with limit equilibrium methods to evaluate the Factor of Safety of a proposed open pit slope. Point estimation involves the use of sample statistics to estimate population parameters. Confidence intervals are constructed that include the value of an unknown variable—in this case Factor of Safety—with high probability. The confidence intervals are developed based on the method of moments from probability theory, which is used to describe random variables of the sample population using the expected value of the random variable and the square of the expected value. A Monte Carlo random sampling method is used to develop a simulated population to approximate a normal distribution, which in this case represents the probability of slope performance defined in terms of the Factor of Safety. This paper describes the process followed to develop the probability density and cumulative distribution functions for the Factor of Safety. The statistical distribution of Factor of Safety is presented and is used to evaluate the pit slope stability in terms of probability of failure and…
Slope Stability 2013 | Abstracts | 40
Risk evaluation of slope considering mechanical and hydraulic characteristics of unsaturated soils
Y-K. Song National Disaster Management Institute, Korea
J-R. Oh National Disaster Management Institute, Korea
M.S. Jung National Disaster Management Institute, Korea
Y.J. Son National Disaster Management Institute, Korea
AbstractRainfall is an important triggering mechanism of slope failure which accompanies severe
damage and loss of life and property. Slope failure is mainly triggered by a deepening of the wetting band accompanied by a decrease in matric suction induced by water infiltration. Early warning methods for slope failure in Korea only tend to use rainfall intensity and duration as the main variables, not considering mechanical and hydraulic characteristics of unsaturated soils. In this study, geotechnical properties of unsaturated weathered soil, including basic physical properties, soil-water characteristics curve, unsaturated permeability curve, and unsaturated shear strength, were investigated in test beds in which slope failures frequently occurred. Also presented is a procedure for the risk evaluation of slope failures, which integrates the Factor of Safety of the infinite slope of unsaturated soil, considering not only rainfall intensity and duration, but also the mechanical and hydraulic properties of unsaturated soils.
Slope Stability 2013 | Abstracts | 41
Analysis of failures in open pit mines and consideration of the uncertainty when predicting collapses
A.G. Cabrejo-Liévano GroundProbe Pty Ltd, Australia
AbstractThe Inverse Velocity (IV) Method, by Fukuzono (1985), has been used in the mining industry
along with slope monitoring radars for almost a decade to predict collapses, with significant successes but also with certain limitations due to the uncertainty associated with the method and the characteristics of the different mechanisms of failure in rock masses.
This paper summarises the results of research undertaken on 74 pit wall failures, on high and low walls, in different type of mines all over the world, since 2004. Only the characteristics of the failures associated with the application of Fukuzono’s method are discussed.
The results are presented statistically, aiming to illustrate the different values of inverse velocity at collapse that could be achieved and the possible errors when forecasting the time of collapse. Keeping in mind the variability of results are essential to a successful risk management at any open pit mine.
Some discussions on the type of inverse velocity plots and its possible association to different failure mechanism are also presented for geotechnical practitioners to be aware of when forecasting collapses.
Slope Stability 2013 | Abstracts | 42
Managing slope performance in uncertain geological conditions at Meandu Mine, Queensland
J.V. Simmons Sherwood Geotechnical and Research Services, Australia
D.C. Edwards Downer EDI Mining Pty Ltd, Australia
N. Ferdinands Stanwell Corporation Limited, Australia
AbstractThe Ground Control Management Plan at the Meandu Mine provides the basis for the
approval of slope designs and operational activities in a coal deposit sequence characterised by complex sedimentation, thick seams, faults, an eruptive volcanic cover sequence, and multiple episodes of deep weathering. Rapid lateral and vertical variations in geotechnical conditions imply that the overburden model for mine planning includes significant uncertainties for slope hazard and stability risk assessment. The paper provides a description of the evolution of slope designs and circumstances that have shaped the current approach to short-term design and operational hazard management Long-term slope design considerations also include the groundwater regime and the placement of both coal washery tailings and power station ash slurry in mined-out voids.
Slope Stability 2013 | Abstracts | 43
Iterative geotechnical pit slope design in a structurally complex setting: a case study from Tom Price, Western Australia
D.S. Lucas Mining One Consultants, Australia
P.J.H. de Graaf Rio Tinto Iron Ore, Australia
AbstractRio Tinto Iron Ore’s (RTIO) Tom Price open cut mine in the Pilbara region of Western Australia
commenced in 1966 and had a cumulative production to mid 2012 estimated at over 800 Mt. The South East Prongs (SEP) pit at Tom Price hosts one of the mine’s prime sources of high grade and low impurity hematite ore. An integrated mine planning and geotechnical design approach was required to evaluate and optimise late stage mining design options within large scale structural geological (adverse bedding strength anisotropy and fault) and hydrogeological controls.
The SEP pit is structurally complex. The orebody is hosted within a doubly-plunging syncline bounded by the low-permeability shale, with predominant east-west striking faults confining the mineralisation to within the central part of the syncline. Multiple deformation events have resulted in significant folding and additional faulting. The complex structural geology, with bedding dipping into the pit void, and numerous faults, present a challenging geotechnical environment to design and implement robust mine design to maximise late stage mining ore recovery.
By mid 2010, the SEP pit had been mined to between 600 and 640 RL. Mining ceased after accelerated movement was detected in the north wall. Additional geotechnical investigations were undertaken in late 2010 and 2011. This augmented information obtained from previous investigations. Stratigraphic units and faults were defined by mapping and geophysical logging, but areas of uncertainty remained, particularly in some fault locations, which could not be improved by further drilling.
The planned final 375 m high pit shell is to extend 30 to 70 metres deeper than the current mining levels, and about 100 m below the regional water table. A modified pit design was required to fit within a constrained region of the pit, to minimise the likelihood of fault controlled instability impacting the main access ramp on the west wall, and to account for dewatering and depressurisation requirements.
The project geotechnical team, consisting of RTIO geotechnical personnel and their geotechnical consultants (Mining One) worked closely with RTIO’s mine design team to develop workable risk assessed options which enabled an optimum design to be adopted, with a detailed hazard and risk management plan for implementation during mining.
The final design was optimised to allow access by a large equipment fleet for more efficient mining, while deferring key geotechnical risks to a later stage of mining to provide greater reliability of ore supply for the short-term mining schedule and opportunity to improve design reliability as mining proceeds.
Slope Stability 2013 | Abstracts | 44
Slope design at Cuajone Pit, Peru
E. Hormazabal SRK Consulting (Chile) S.A., Chile
R. Veramendi Southern Peru Copper Corporation, Peru
J. Barrios Southern Peru Copper Corporation, Peru
G. Zuñiga SRK Consulting (Chile) S.A., Chile
F. Gonzalez SRK Consulting (Chile) S.A., Chile
AbstractThe Cuajone porphyry copper deposit is located on the western slopes of Cordillera
Occidental, the southern Andes of Peru. The current pit measures about 2.5 km east–west, 3.0 km north–south, and at the end of 2012, had a maximum depth of 950 m. Mining by open pit methods commenced in 1976 and has continued since that time. Ore production is 80 ktpd.
As part of the slope design program and slope optimisation, the past and present performance of the pit slopes was evaluated to provide information on the potential behaviour of future pit expansion. A geomechanical assessment is being carried out to evaluate the stability of the walls of the next expansion. To evaluate the stability of the open pit, a series of geotechnical studies have been performed. These studies involve, among others, slope stability analyses based on limit equilibrium methods and finite element numerical models. In addition, a detailed back-analysis of a five million ton failure (DSE42) was performed to calibrate rock mass properties and to understand slope behaviour in poor rock mass quality.
This paper describes the back-analysis of the DSE42 failure and the slope design process for the current pit and next pushback.
Slope Stability 2013 | Abstracts | 45
Three-dimensional limit equilibrium analysis of open pits
H.H. Lu SoilVision Systems Ltd., Canada
M.D. Fredlund SoilVision Systems Ltd., Canada
D.G. Fredlund Golder Associates Ltd., Canada
AbstractThe analysis of slope stability in the design and ongoing operations of any particular open
pit remains a difficult challenge. Slope failures and loss of equipment, mining time, and lives make stability concerns an issue which warrants research efforts. Engineers have relied for decades on software tools to perform analysis of the slopes of open pits in order to estimate the Factor of Safety (FS). Usually open pit geometry is typical three-dimensional (3D) geometry which cannot adequately be simplified into a two-dimensional (2D) plane strain representation. Traditional analysis has been performed using 2D limit equilibrium methods (LEM) since this method continues to be the simplest to apply. This paper examines the application of the 3D LEM to analyse the slopes of an open pit. The 3D LEM has advantages in that it can consider slips at any particular azimuth vector angle (i.e. it can search the whole 3D open pit model and find the critical slip surface, and critical slip vector). The results of 3D LEM are compared with results from 2D LEM analysis. The result is a methodology which is credible and applicable within a reasonable time frame for the analysis of open pits.
Slope Stability 2013 | Abstracts | 46
Integrated slope stability assessment in a complex geotechnical and hydrogeological setting
R. Campbell SRK Consulting (UK) Ltd, UK
D. Mackie SRK Consulting (Canada) Inc., Canada
W.S. Anderson Teck Resources Ltd., Canada
AbstractIntegration between geotechnical and hydrogeological groups for slope stability studies
is often discussed but more rarely appropriately implemented. Although guidelines exist, experience has shown that the communication and technical integration between the geotechnical and hydrogeological teams can be problematic. This paper presents an example of a holistic integration process which builds on established best practice guidelines rather than attempting to re-invent the currently accepted methodology. The Galore Creek copper-gold project, located in northwestern British Columbia, has been chosen as an illustrative case study.
The Galore Creek copper-gold deposit, owned by the Galore Creek Mining Corporation (GCMC), currently includes plans for three open pits and additional mining-related infrastructure. The proposed mining area is surrounded by high, rugged, and ice-capped mountains on three sides with the Galore Valley opening to the north. The area experiences high levels of precipitation (rainfall and snow), as well as a significant annual freshet period. Combined with challenging topographic and climactic conditions, pit wall stability will be influenced by a structurally complex, variable rock mass, and locally elevated and compartmentalised pore water pressures.
From the project outset, it was determined that an integrated approach to slope design would be required to consider the prevailing physical and environmental factors at play in the Galore Valley. To achieve the slope design in a practical and timely manner, both consultant and client geotechnical and hydrogeological teams met regularly from the initial planning and investigation stage through to the final stability modelling of the proposed pit slopes.
With targeted field investigations providing the framework to update rock mass, structure, and hydrogeological characterisation, a number of potentially unstable zones within the mining area were highlighted. Elevated pore water pressures, combined with a locally weak rock mass and significant slope heights (in excess of 1,000 metres), required constant interaction between the geotechnical and hydrogeological groups to ensure that appropriate inputs and material behaviour were represented within the numerical stability models. A number of pore water pressure scenarios were evaluated including average freshet and full dewatering system failure. These varied pore water pressure scenarios were assessed and exported as 2D sections for limit equilibrium and finite element slope stability modelling.
With the project schedule in mind, the hydrogeological and geotechnical teams were required to constantly exchange ideas and information since slope geometry had to remain flexible due to the evolving pit designs. Regeneration of pore pressure grids, for input into numerical stability models was not practical due to time constraints during this period. Phreatic surfaces…
Slope Stability 2013 | Abstracts | 47
Geotechnical reliability assessment of a large counterfort retaining wall
W. Deng Aurecon Pty Ltd, Australia
K. O’Neill Aurecon Pty Ltd, Australia
K. Luu Aurecon Pty Ltd, Australia
K. Little Baulderstone Construction, Australia
AbstractIn the development of Barangaroo Headland Park in Sydney, a retaining wall was required
to retain up to 18.5 m of fill and to form a physical barrier between the Headland Park fill and the Future Cultural Space. To minimise the quantity of imported select fill to the site and to provide a more impenetrable barrier to water and odours, a reinforced concrete counterfort wall solution was derived in conjunction with an anchoring system to reduce the base width. The counterfort wall is constrained by the adjacent excavation for the Future Cultural Space which is approximately 7 m deep and up to 7 m away from the proposed counterfort wall face.
Due to the significance of the structure, a supplementary geotechnical reliability assessment of the counterfort wall failure was undertaken in addition to the deterministic geotechnical design and assessments based on AS5100.3 in the detailed design stage. This paper presents the geotechnical reliability assessment carried out. The project background, and the elements of works which are relevant to the counterfort retaining wall, are introduced. The underlying ground conditions and geotechnical uncertainties are then described, with the assessment of the most likely values of the geotechnical parameters involved in computing the Factor of Safety by the deterministic method, and the standard deviations of the parameters that involve uncertainty and risk. The probabilities of failure for various geotechnical failure modes are then assessed. The major contributors to the standard deviation of the Factor of Safety are identified and measures to reduce these uncertainties that informed to the design are discussed. Finally, the significant contribution of the geotechnical reliability analysis to the detailed design of the counterfort wall is summarised, and remarks on the application of a reliability assessment in geotechnical design are made.
Slope Stability 2013 | Abstracts | 48
Towards developing a more rigorous technique for bench scale slope stability analysis in hard rock
R. Teet AMC Consultants Pty Ltd, Australia
A. Vakili AMC Consultants Pty Ltd, Australia
A. de Veth AMC Consultants Pty Ltd, Australia
AbstractThe mining industry is a strong but volatile market that is focused on future growth through
expanded production, increased operational efficiency and cost optimisation (Ernst and Young, 2013). As operational expenditure increases and the readily minable ore is extracted, the technical challenges facing mining are becoming more prevalent. With increased depths of open pit operations, the need to minimise the footprint of the mine and limit pre-stripping requires the optimisation of slope geometry and configurations in such a way that extraction is maximised without increasing risk to personnel, equipment or mine life. An essential component of the slope optimisation process is the rigorous geotechnical assessment of the stability of the pit walls at bench, inter-ramp and overall slope scale.
Advancements in computational power and numerical modelling have significantly progressed the analysis of overall slope and inter-ramp scale stability. However the current industry standard methods of bench scale stability analysis still heavily rely on empirical, kinematic and limit equilibrium techniques. These techniques are adequate for scoping and pre-feasibility level projects where the data availability is limited and the confidence in results restricted. In contrast, as the pit develops and progresses into feasibility to implementation stages of development, optimisation becomes a more significant component of the geotechnical assessment and more rigorous analytical methods should be employed.
This paper introduces an improved analytical method that integrates discrete fracture network (DFN) generation and kinematic analyses for bench scale slope stability analysis. Conventional kinematic analyses were conducted on a representative data set and the resulting probability of failure (POF) compared to a POF generated from a calibrated stochastic DFN model. Results showed that the conventional analysis was conservative in nature due to the inability to assess the influence of discontinuity interaction and spacing on the resultant wedge. The authors’ experience of recent technical work had also flagged a dissimilarity between the conventional kinematics and real world observations. Additional numerical modelling utilising a pseudo-discontinuum modelling technique was conducted in an attempt to quantify the extent of the conservatism seen in conventional versus alternative methods of bench scale stability assessment.
The ability to incorporate a holistic DFN approach to the assessment of batter scale stability facilitates the optimisation and risk reduction process. The limitations of this alternative method are not fully established and further validation and testing is needed however, potential does exist for the inclusion of DFNs in kinematic bench scale assessments and the subsequent…
Numerical analysis
Slope Stability 2013 | Abstracts | 50
Characterisation and stability modelling in weak rock masses of the Robinson Mine
M. Fournier Knight Piésold Ltd., Canada
R. Mercer Knight Piésold Ltd., Canada
D. Yang Knight Piésold Ltd., Canada
J. Miller KGHM Inc., USA
AbstractThe Robinson Mine is a large porphyry copper deposit located approximately 400 km north of
Las Vegas in central Nevada. Large scale open pit mining operations started in 1908, but ceased in 1978. The property was re-opened in 2008 and the mine currently consists of five open pits. Since 2012, the mine has been operated by KGHM Inc. with a focus on expanding and deepening the Ruth pit. The pit walls were largely developed with 15 m high benches and an inter-ramp angle of 36°. This wall configuration was largely based on a pit geotechnical study in the early 1990s.
In 2011, excessive slope deformation and wall failures were observed along the 300 m high north wall. The deformations were primarily within the Chainman Shale, which forms the lower half of the wall. Initial deformation control and risk mitigation efforts focused on surficial flattening of the deforming materials and on the installation of a slope monitoring radar system. By December, the mine was forced to discontinue mining in the area, which has had a significant impact on the mine plan. Preliminary back−analyses in early 2012, suggested that a circular-type failure was occurring within the highly altered and weak shale and that this unit appeared to be degrading over time The back-analyses also suggested considerably lower strengths for this unit than what was being utilised in the existing pit slope design. A geotechnical drilling program was undertaken to better understand the rock mass characteristics at these depths and to support updated slope recommendations.
The results of the drilling program suggested high core recoveries in the shale and the rhyolite, even though many sections of the drill core could be crushed by hand. The rock mass was classified using the RMR system, with low ratings assigned to the low quality intervals via adjustments derived from GSI mapping of available surface exposures. Triaxial and direct shear laboratory testing was also taken on the soil-like materials. The results of this work suggested that the strategically employed RMR classification, coupled with a Hoek–Brown model, may not adequately capture the strength condition for a rock mass that varies spatially between regions of intact rock and soil-like materials. In general, the back-analysis models show considerable deviation from what would be considered as the expected condition, given the rock mass characterisation and laboratory testing available. The incorporation of a disturbance zone into the slope stability analyses overcame some of these limitations and resulted in a better match to observed slope performance.
Slope Stability 2013 | Abstracts | 51
The use of numerical modelling, slope monitoring and operational procedures to manage slope deformations at the Ranger 3 pit
D.R. Wines Itasca Australia Pty Ltd, Australia
I. Hulls Mining One Consultants, Australia
E. Woods Energy Resources of Australia Ltd, Australia
A. Creighton Rio Tinto, Australia
AbstractElevated slope movements were observed on the northeast wall of the Ranger 3 pit during
excavation of the final pit shell. Both prism and radar monitoring indicated that the movement rate and magnitude were greater in this area when compared to surrounding areas, and periods of acceleration were evident. Several months after the initial onset of movement, tension cracks were observed behind the upper pit crest. At that stage, several benches were yet to be mined at the base of the wall, and concern existed regarding the safety of operations below the moving wall.
A calibrated three-dimensional numerical model was selected as the prime risk management strategy for mining the balance of the attainable ore in Pit 3. A detailed structural geological study was initially undertaken to provide reliable inputs for the modelling. The modelling was integrated into the overall risk management process, with the model being constantly updated based on the observed slope behaviour and the rock mass conditions being exposed at the toe of the slope. Ongoing and detailed calibration between the model behaviour and the comprehensive slope monitoring data was performed to provide a reliable understanding of the mechanism of movement, and to assess the likelihood of slope failure. Possible failure scenarios were also examined as a part of the risk management strategy, and strict operating procedures were implemented to minimise the risks associated with mining under an actively moving pit wall.
Although the modelling indicated that ongoing slope movements could be expected, slope failure was not predicted, provided that final pit excavation would be completed, as planned, prior to the upcoming wet season. In light of these modelling results, mining continued in Pit 3 based on the original mine plan, and final pit excavation was successfully completed in late 2012. Backfilling of the pit commenced soon after. After initial discovery of the tension cracks, some consideration had been given to incorporating a step-out in the lower part of the wall in an attempt to stabilise the observed movements. The successful risk management process, including detailed numerical modelling, comprehensive slope monitoring and strict operational procedures, allowed the original mine plan to be achieved, and therefore avoided the significant loss of ore associated with the proposed design change.
This paper summarises the numerical modelling methodology and results, the monitoring…
Slope Stability 2013 | Abstracts | 52
Incorporating brittle fracture into three-dimensional modelling of rock slopes
M. Havaej Simon Fraser University, Canada
A. Wolter Simon Fraser University, Canada
D. Stead Department of Earth Sciences, Simon Fraser University, Canada
Z. Tuckey Coffey Mining Pty Ltd, Australia
L. Lorig Itasca Consulting Group Inc., USA
E. Eberhardt Department of Earth and Ocean Sciences, University of British Columbia, Canada
AbstractDuring the last decade significant advances have been made in the two-dimensional
modelling of brittle fracture associated with rock slope failure both in open pit mines and natural mountain slopes. This paper focuses on the application of the three-dimensional lattice code, Slope Model, in modelling brittle fracture and damage evolution involved in three-dimensional kinematically-controlled slope instability mechanisms. Results of simulations of non-daylighting wedge failure and active-passive block slope failures are presented, with an emphasis on characterising brittle damage at varying stages of slope failure development. A new approach to characterising brittle fracture damage is developed based on fracture generation rates and the inverse velocity of the failing rock mass. Brittle fracturing of ‘in-plane’ and ‘out−of−plane’ rock bridges is simulated using a conceptual approach incorporating a simple Discrete Fracture Network (DFN) into simulations. In order to simulate the complex geometry associated with three−dimensional slope failures, pre-processing routines have been developed to incorporate photogrammetric and LiDAR derived Digital Elevation Models (DEMs) within the Slope Model software. Procedures are demonstrated through the use of preliminary Slope Model simulations of the Vajont landslide, a major catastrophic landslide, which resulted in the loss of over 2,000 lives.This paper summarises the numerical modelling methodology and results, the monitoring methods and data and the operational procedures that were used to successfully manage final pit completion.
Slope Stability 2013 | Abstracts | 53
Open pit numerical model calibration using a pseudo three-dimensional radar monitoring technique
J. Severin SRK Consulting (Canada) Inc., Canada
E. Eberhardt Department of Earth and Ocean Sciences, University of British Columbia, Canada
S. Fortin Teck Resources Ltd., Canada
AbstractSlope monitoring plays an important role in the calibration of numerical models created to
investigate the mechanics of large open pit slopes. Geodetic prisms are often relied upon to delineate the boundaries of potential slope hazards; however the data can be limited by its point-measurement nature. Localised displacements at each prism may be misinterpreted when extended to the behaviour of the entire slope, and important displacements between prisms may be overlooked. A novel experiment was conducted in which two ground-based synthetic aperture radar systems were simultaneously deployed to record continuous, line-of-sight displacement of an open pit slope in ‘stereo’. The displacement vectors were combined to create a pseudo 3D displacement map of the pit slope consisting of over 25,000 monitoring points. The data collected demonstrated that an improved understanding of the 3D kinematics of a large rock slope can be achieved using advanced state-of-the-art monitoring techniques to aid mine design. The displacement data as well as the understanding of the slope kinematics were then used to calibrate a numerical model of the current pit slope created using 3DEC, a 3D distinct element modelling code. Rock mass and fault properties were modified until the response observed in the model was more representative to that of the monitoring data throughout the slope face. Rock mass response to mining-induced stress was shown to vary over several different parts of slope, including the areas adjacent to the main faults within the slope.
Slope Stability 2013 | Abstracts | 54
Two-dimensional and three-dimensional distinct element numerical stability analyses for assessment of the west wall cutback design at Ok Tedi Mine, Papua New Guinea
I.A. de Bruyn SRK Consulting (Australasia) Pty Ltd, Australia
M.A. Coulthard M.A. Coulthard and Associates Pty Ltd, Australia
N.R.P. Baczynski Ok Tedi Mining Ltd, Papua New Guinea
J. Mylvaganam SRK Consulting (Australasia) Pty Ltd, Australia
AbstractDetailed evaluations for finalisation of the design for the west wall cutback at the Ok Tedi
copper-gold mine in Papua New Guinea have been ongoing since 2010. The geotechnical rock mass characterisation, structural model and conceptual hydrogeological model have been progressively updated since 1997, and have been significantly advanced during recent feasibility studies. The pit is being progressively deepened with ongoing mining, and a cutback of the west wall is being planned that would result in a final wall height of 1,000 m. The wall will be cutback by up to 300 m over a crest length of greater than 1,500 m, which will take place over a period of approximately 13 years.
A comprehensive set of 2D distinct element analyses were completed in 2011 for assessment of the stability of the west wall final design. Depressurisation of the cutback slope was indicated to be of great importance, and measures for depressurisation were taken into account in the supporting analyses. Additional field investigations and assessments for confirmation of the design performance were carried out in 2012 and are ongoing in 2013. The key aspect of this work involved further distinct element analyses for assessment of the slope performance in three dimensions, particularly in the context of the effects of major structures, joint sets, pit wall curvature and pore water pressures as the slope cutback is developed. The extreme size and complexity of the 3D model necessitated simplifications to the geotechnical domains and structural inputs in order to create a practical working model. As expected, the 3D analyses provided Factors of Safety for slope instability significantly greater than those obtained from the original 2D analyses. However, it is most important to understand the context and limitations of these results when making final decisions on design outcomes. For this reason, selected additional 2D analyses were carried out in order to assess the sensitivity of the results to simplifications in the geotechnical domains and structural inputs and to the coarser block size necessary for the very large 3D model.
Slope Stability 2013 | Abstracts | 55
Three-dimensional numerical stability analysis of the Oyu Tolgoi open pit
M. Smithyman Golder Associates Ltd., Canada
H. Puebla Golder Associates Ltd., Canada
A. Chance Golder Associates Ltd., Canada
R. Beddoes Golder Associates Ltd., Canada
A. Creighton Rio Tinto, Australia
AbstractThree-dimensional (3D), stress-deformation models are useful for analysing the stability of
complex 3D problems in open pit mine slopes. Stress-deformation models are very powerful because in addition to the Factor of Safety, the states of stress and strain throughout the pit are computed in a single model where a large number of potential failure mechanisms may be considered simultaneously. However, the massive quantities of information provided by these models make them difficult to interpret.
This paper presents and discusses a FLAC3D, version 4.0 (Itasca, 2009) numerical model that was developed to assess the stability of the proposed Oyu Tolgoi open pit, which will be approximately 2,900 × 2,100 m wide, and 600 m deep once it is completed. This large pit will include two distinct sub-pits that will have numerous fault intersections within the pit walls that cannot be adequately represented and assessed by 2D slope stability analysis models.
The FLAC3D model of the proposed Oyu Tolgoi open pit focused on assessing 3D complex failure mechanisms that involve one or more of the steeply dipping faults within the pit walls at two critical stages over the life-of-mine. This model allowed consideration of the pit stability from a stress-deformation perspective. While this approach can be used to assess pit stability in cases where very large displacements associated with well-defined failure mechanisms are computed (e.g. catastrophic failure), assessing the large scale structurally controlled stability is more challenging if a catastrophic failure is not predicted.
In this analysis, a number of methods were considered to determine the overall and local stability of the pit slopes. The following characteristics were considered: i) displacements, ii) strains, iii) velocities, iv) the yielding state of the model elements, and v) FLAC3D’s internal Factor of Safety calculation.
The automated Factor of Safety (FS) calculation within FLAC3D provides only the single most critical failure in the model. In the case of the Oyu Tolgoi open pit, the computed FS was relatively large and not related to 3D complex failure mechanisms involving the faults within the pit walls. Had the model been be set up to focus only in specific mechanisms of interest, the computed FS would have been larger, but nothing more than another number. From this perspective, the FS calculation was found of limited use in this case and hence, other information from the stress-deformation analysis was used to assess the stability of the pit slopes beyond the…
Slope Stability 2013 | Abstracts | 56
Three-dimensional analysis of pit slope stability in anisotropic rock masses
D.P. Sainsbury Mining One Consultants, Australia
B. Sainsbury Castlemaine Goldfields Ltd, Australia
AbstractAnisotropic and foliated rock masses, the behaviour of which are dominated by closely spaced
planes of weakness, present particular difficulties in the assessment of pit slope stability. Various numerical modelling techniques are available that explicitly simulate the joints and discontinuities within an anisotropic rock mass. However, due to the computational intensity of these numerical techniques, it is not practical to explicitly simulate the joint fabric of an entire three-dimensional pit slope for routine stability assessment. In order to simulate the effects of anisotropic rock mass strength and deformation behaviour on pit slope stability, a modelling methodology has been developed to account for rock mass anisotropy and scale effects using a continuum based ubiquitous joint constitutive model. This paper outlines the anisotropic modelling methodology and presents a series of demonstration models that have been used to validate the technique.
Slope Stability 2013 | Abstracts | 57
UDEC and RFPA2D simulations on the influence of the geometry of partially-spanning joints on rock mechanical behaviour
P.L.P. Wasantha Civil Engineering Department, Monash University, Australia
P.G. Ranjith Civil Engineering Department, Monash University, Australia
T. Xu Northeastern University, China
AbstractThe Authors used Universal Distinct Element Code (UDEC) and two-dimensional Rock Failure
Process Analysis (RFPA2D) programs, which use the Discrete Element Method (DEM) approach and the Finite Element Method (FEM) approach, respectively, to simulate the mechanical behaviour of rock-like materials with partially-spanning joints in different geometries. The results from the two programs were compared with the results of an experimental study, conducted on cement-mortar specimens with partially-spanning joints in different geometries, in order to evaluate the feasibility of the two programs in simulating the mechanical behaviour of rock-like materials with partially-spanning joints.
Three different partially-spanning joint geometrical properties, i.e. joint location, orientation and trace length, were considered in numerical simulations using both UDEC and RFPA2D and the experimental study. For partially-spanning joint location, both numerical programs produced reasonably consistent results with experimental results for the variation of Uniaxial Compressive Strength (UCS) against joint location, especially for higher values of joint location. However, considering the overall variation of UCS against joint location we proposed that the joint location is of negligible influence on the UCS of the rock. Variations of UCS against partially-spanning joint orientation for the experimental work and UDEC simulations were observed to match very closely, whereas RFPA2D results have underestimated the UCS for all joint orientations. The selection of continuously yielding joint constitutive model for the joints in UDEC simulation, which is more representative of the joints used in the experimental study, can perhaps be the reason for the more accurate replication of experimental results using UDEC. Moreover, both numerical simulations verified the result observed in the experimental study in which the UCS of test specimens is minimal when the partially-spanning joint is orientated at an angle of 45°. The strain distribution characteristics obtained from both numerical programs generally agreed. The fact that when the joint is oriented in 45° angle, the influence from the joint on failure of rock is maximum and with increasing and decreasing joint orientations from 45°, the contribution from the joint for the rock failure is less. The UCS of test specimens was observed to decrease linearly with increasing joint trace length from the results of the experimental study, and the results of numerical simulations from both numerical programs showed a reasonably good agreement with the experimental results. According to the strain distribution characteristics of the experimental and numerical simulation results from both programs, relatively longer partially-spanning joints can significantly influence the failure of test specimens, whereas samples with relatively…
Slope Stability 2013 | Abstracts | 58
Slope stability analysis at Siilinjärvi Mine
S. Mononen Yara Suomi Oy, Finland
H. Kuula Pöyry Finland Oy, Finland
M. Lamberg Pöyry Finland Oy, Finland
AbstractSiilinjärvi phosphate mine in eastern Finland has been in operation as an open pit since 1979.
The current main pit, the Särkijärvi open pit, is 2,900 m in length, 235 m in depth and at its widest part 750 m wide. The ore feed to the mill is close to 11 Mt/a. The stripping ratio in current LOM (mine life to 2034) is on average 0.6 but a major extension program is ongoing and for the next nine years the stripping ratio will be around 1.2. Part of the main pit extension program involves new infill drillings, altogether 39 km in 2012–14. The updated geological and rock mechanics data is and will be used in slope stability analysis. Engineering company Pöyry Finland Oy is developing rock mechanics analyses and delivering guidance’s to the mine engineering team.
The Siilinjärvi carbonatite complex is a steeply dipping Archean vein intrusion that has intruded into granite gneiss. The complex is approximately 16 km long. The main rock types are calcite carbonatite, glimmerite and their varieties depending on the amount of apatite and calcite. The carbonatite is surrounded by a fenite halo. The geology in the mine is challenging as seen from a rock mechanics perspective. The glimmerite rock has poor rock quality and a low uniaxial compressive strength. The glimmerite has a similar major joint direction as the intrusion general strike and dip which is noted as a weakness plane for the rock mass. The glimmerite rock mass was partly highly sheared due to late/post intrusion tectonics. The shear zones consist of an extremely weak rock mass and have high water loss values.
Geotechnical characterisation of the rock mass has been carried out using Q – and GSI systems. The rock quality was mapped directly from the open pit walls and from drill holes. Also 3D-photogrammetry was used to map joints and shear zones in the pit.
The stability analysis was performed using the distinct element program, 3DEC. The rock mass was modelled as a Mohr-Coulomb elastic, perfectly plastic continuum. Analysis used a shear strength reduction approach: the shear strength envelope of material was reduced by a Factor of Safety until the velocities in the model are not balanced. Because of limited groundwater data simulations were made with drained and almost fully saturated conditions.
The lowest safety factor was found to be in the weak rock mass area where the safety factor for overall stability was 1.6 in saturated slope and about 1.9 in drained slope. In individual benches the lowest safety factors varied from <1 to 1.2. For the detailed parametric study 2D analysis was also made with Phase 2. The cross section was taken through the middle part of the open pit. In 2D analysis the extent of the disturbance zone and groundwater table was studied.
The stability analysis was performed in order to identify potentially unstable areas. From those areas collection of groundwater data will be substantially increased. Also additional geotechnical core logging and mapping will be executed. To monitor the stability of the open pit, purchasing of slope stability radar is under consideration by the mine…
Slope Stability 2013 | Abstracts | 59
The effect of slope curvature in rock mass shear strength derivations for stability modelling of foliated rock masses
S. Narendranathan Coffey Mining Pty Ltd, Australia
R.D.H. Thomas Coffey Mining Pty Ltd, Australia
J.M. Neilsen Coffey Mining Pty Ltd, Australia
AbstractIn open pits the instability mechanisms are multifaceted involving; shearing along or over the
asperities of the defect surface and/or block rotation at very low normal stresses. At higher degrees of confinement, shearing along or through asperities and block rotation including rock mass failure due to intact rock breakage can occur. It is common to have pit designs with varying profiles resulting in concave, straight and convex geometries. This difference in wall geometry would result in varying magnitudes of effective shear strength being mobilised. The contribution of the lateral confinement to the degree of shear strength mobilised is often overlooked in design. In this paper a case study will be presented, which compares the different slope performance outcomes within similar geotechnical conditions with the only variant being the slope geometry and the influence of lateral confinement. An algorithm is developed, based on observations from this site case study, linking the concavity of a slope face to the degree of (extra) shear strength mobilised. It is the authors intent that this algorithm can be used in a similar manner to which highway engineers use ‘curve-speed models’ to determine safe approach speeds for corners given a particular road curvature, (in our case pit slope concavity) and approach speed (rock mass characteristics). This relationship has been implemented for forward analyses at the mine in question; however the authors acknowledge that further work needs to be undertaken so as to ensure the validity of the relationship for generalised application.
Slope Stability 2013 | Abstracts | 60
Stability analyses for a large landslide with complex geology and failure mechanism using numerical modelling
B. Wentzinger Golder Associates Pty Ltd, Australia
D. Starr Golder Associates Pty Ltd, Australia
S. Fidler Golder Associates Pty Ltd, Australia
Q. Nguyen ATC Williams Pty Ltd, Australia
S. Hencher Steve Hencher Associates Ltd, UK
AbstractGeotechnical studies were undertaken for a large landslide which occurred during the
construction of the South West Transit Corridor, in South East Queensland, Australia. The site investigation revealed complex geology comprising trachyte flows extruded on top of sediments and basalt flows. The evolution of the landslide was monitored using surface survey, inclinometers, piezometers and observation wells. The results of the site investigation, geological mapping, laboratory testing program and monitoring were used to prepare a geotechnical model for stability analyses.
The development of the geological and geotechnical models is briefly discussed, and the methodology used to define the failure mechanism and calibrate the model is presented and discussed. Various methods and software packages were trialled in order to model the complex failure, geology and groundwater conditions. The shape of the failure surface was defined using the results of the movement monitoring devices and surface observations of tensions cracks. The assumptions made in defining the failure surface shape and strength properties are presented.
The final numerical model was validated using back-analysis with ground water conditions known to trigger movements, and the material properties along the shear surface were compared with the results of laboratory strength tests. The methodology used to estimate the Factor of Safety against reactivation of the movements using numerical modelling is presented. The use of the model to develop remedial measures is also discussed.
Slope performance
Slope Stability 2013 | Abstracts | 62
A web-based GIS decision support system for slope stability monitoring data interpretations and visualisation management
A.B. Firman PT Adaro Indonesia, Indonesia
C.D. Wiratno PT Adaro Indonesia, Indonesia
S. Bahri PT Adaro Indonesia, Indonesia
H. Timbul PT Adaro Indonesia, Indonesia
AbstractThis paper illustrates how the application of web-based Geographic Information Systems (GIS)
to store and visualise the slope monitoring data performed by Robotic Total Station (RTS) and Slope Stability Radar (SSR) into an interactive map on the web. Since 2004 PT Adaro Indonesia has been developing an advanced slope monitoring system to monitor slope stability of its open pit mines. As one of the world’s largest, with a mining area of nearly 45,000 hectares, PT Adaro’s single open pit mine boasts of 13 RTS’s supported by 800 active monitoring prisms scattered throughout the mine area. Later in 2009, SSR Groundprobe was developed to complement the automatic monitoring system already in place. Nowadays there are two SSRs (SSR SSR X–089 and XT–135) that monitor movement on the specific pit slopes of concern. From the results of the automatic slope monitoring system performed by RTS and SSR, the information is taken as the value of the movement that occurs in each respective area or waste dump. If the movement of a slope exceeds a predetermined trigger level, then it can be taken in the form of changes in mine design controlling evacuation or any type of work (including the mining activity) done in the affected area to avoid the risk of equipment damage caused by a catastrophe, such as landslide. For long term purposes, data from the RTS and SSR can be used as supporting data for further Geotechnical analysis to get an overview of the characteristics of a slope in a particular area.
Database management of large amounts of data from the continuous monitoring slope movements by the RTS and the SSR, presents frequently occurring obstacles that needs special attention. One challenge lies in the presentation in real time mode since previous data should not be ignored as they depict sustainability. From the data can be easily managed using the SQL (Structured Query Language) server-based Leica GeoMos software that is capable of managing unlimited amount of data, and if necessary do the query, analysis, and database modifications via the SQL server enterprise software. Another challenge is the SSR data management, where data is managed manually using wall folders that have limitations of just two weeks, and can only be performed exclusively using SSR Control software.
To overcome these obstacles, one effective way is to develop a GIS database for organising slope monitoring data. In order to deliver slope monitoring data in a more effective and interactive, a web-based GIS applications can also be developed. With this WebGIS, mine slope stability monitoring information can be easily and quickly accessed because it is web based…
Slope Stability 2013 | Abstracts | 63
Can full waveform technology enhance the use of terrestrial laser scanning to monitor rock slope deformation?
J.G. Williams Department of Geography, Durham University, UK
N.J. Rosser Department of Geography, Durham University, UK
A. Afana Department of Geography, Durham University, UK; and 3D Laser Mapping Ltd, UK
G. Hunter 3D Laser Mapping Ltd, UK
R.J. Hardy Department of Geography, Durham University, UK
AbstractThe reliable monitoring of slope deformation is a significant parameter for mitigating landslide
damages, including business disruption and danger to workers. Despite this, remote sensing of surface deformation used to interpret failure mechanisms at the shear zone remains limited by factors such as the resolution and viewing angle of monitoring. Here we present an analysis of data captured using a new generation of full waveform terrestrial laser scanners (FW-TLS), which offers potential gains for near real time rock slope monitoring. This approach, having evolved from recent advances in airborne LiDAR, resolves the structure of the reflected laser signal (the waveform) from which a series of attributes of the surface character, geometry and deformation are extracted.
The influence of target geometry, analogous to a deforming rock face, on the reflected waveform is interpreted from a set of controlled condition datasets. The analysis highlights the sensitivity of the maximum amplitude, relative to other parameters of the waveform, to changes in target geometry. We conclude by considering the implications for slope deformation monitoring of this new approach.
Slope Stability 2013 | Abstracts | 64
Experience using terrestrial remote sensing techniques for rock slope performance assessment
M. Sturzenegger Klohn Crippen Berger Ltd., Canada
D. Willms Klohn Crippen Berger Ltd., Canada
K. Pate Seattle City Light, USA
B. Johnston Tetra Tech Inc., USA
AbstractThis paper reports on projects, which integrate the advantages of terrestrial remote sensing
techniques to analyse the performance of rock slopes. The first project is concerned with a bench performance assessment of an inactive open pit mine in British Columbia, Canada; this assessment is part of the design work for the proposed pit expansion. The second project involves characterisation of the rock abutments of an operational concrete hydroelectric dam, in the Washington State, USA.
The bench scale stability of mine slopes in blocky to moderately fractured rock mass is primarily determined by structurally-controlled failure mechanisms such as planar, wedge and toppling failure. Conventional design involves the analysis of adversely-oriented discontinuities, which have the potential to generate unstable blocks. These kinematic analyses are used to develop design parameters, including bench face angle, bench width and inter-ramp angle. Bench performance assessment aids in both bench and inter-ramp design, based on detailed quantification of the previously achieved bench geometry.
The first case study is from geotechnical investigation work at Bell Pit, near Granisle, BC. The bench performance assessment in this case utilises terrestrial digital photogrammetry to quantify the achieved bench geometry of the pit walls. The advantages of using remote sensing data as opposed to measurements made at the outcrop include: a more detailed and arguably more accurate dataset, reduction of issues related to access, and reduction of safety concerns due to rock falls. Similar advantages are advertised in the literature concerning remote sensing-based discontinuity characterisation, which is now commonly used in the industry. In this case study, a geometric correction is applied to the measured back-break and effective bench face angle in order to enhance measurement accuracy. A discussion concerning the validity of the assessment is provided.
The second case study involves discontinuity characterisation of the natural rock slope abutments of the Boundary Dam, a concrete hydro-electric dam located along the Pend Oreille River. These abutments show evidence of past rock block failures where blocks failed along discontinuities. Structural mapping using terrestrial remote sensing techniques allows both the characterisation of these discontinuities and the description of past failure mechanisms, which may highlight potential future failure modes. The procedure is carried out along the Pend Oreille River canyon using a combination of terrestrial and vessel-mounted LiDAR (Light Detection and Ranging) point clouds.
Slope Stability 2013 | Abstracts | 65
Powerful rockfall incidents at Al-Hada descent and remedial measures
B.H. Sadagah Faculty of Earth Sciences, King Abdulaziz University, Saudi Arabia
M.S. Aazam Ministry of Transportation, Saudi Arabia
A. Al-Amri Ministry of Transportation, Saudi Arabia
O. Al-Hoseiny Ministry of Transportation, Saudi Arabia
A. Al-Harbi Ministry of Transportation, Saudi Arabia
AbstractAl-Hada descent lies at the western region of Saudi Arabia at elevation of about 2,000 m,
characterised by sharp cliff. Al-Hada descent road was constructed with an elevation difference of 1,300 m between the highest and lowest heights along the road. The road alignment is intersected by eight very steep gullies of almost 45 to 80°. The gullies contain large quantities of mud, old levees and large rock blocks. Al-Hada descent road was hit by heavy rainfall lasting about two hours. The rainstorm initiated rockfalls and debris flows on steep gullies, and caused rock blocks to drop down rapidly along the gully channel. A large rock block unbalanced at high elevation, dropped from a height of about 150 m elevation difference to break three Jersey barriers and cause indents on the ascending and descending roads. This rock block continued downhill to rest on an unstable debris accumulation that received more rolling, sliding and bouncing rocks from higher steep elevations. On scrapping the debris flows at the lower elevation road segment, a number of rockfalls took place too.
The temporary solution was to remove almost 230,000 m3, however unreachable debris accumulation of 65 to 80° inclination was difficult to remove and cannot be accessed. Construction of a gallery was a planned ultimate solution to protect the road from the rockfalls and debris flows. This case history outlines the analysis of rockfall and design of barriers for the Al-Hada descent road.
Slope Stability 2013 | Abstracts | 66
Innovative use of slope monitoring radar as a support to geotechnical modelling of slopes in open pit mines
A.E.E. Escobar Codelco El Teniente, Chile
P. Farina IDS Ingegneria Dei Sistemi, Italy
L. Leoni IDS Ingegneria Dei Sistemi, Italy
C. Iasio IDS Ingegneria Dei Sistemi, Italy
N. Coli IDS Ingegneria Dei Sistemi, Italy
AbstractIn the modern mining industry a comprehensive slope monitoring program, aimed at managing
potential large scale instabilities and able to simultaneously detect local scale movements, should represent an integral part of every geotechnical risk assessment plan.
El Teniente provides a good example of a complex modern mining operation where stability issues have to be addressed with a slope monitoring program which is able to support geotechnical engineers not only in managing risk, but also in the interpretation of ongoing stability problems. Situated in Chile, 44 km east of Rancagua, 75 km south of the capital Santiago and at an altitude of 2,500 m, El Teniente is one of largest underground copper mines in the world and also recently integrated surface mining. The nature of the project in terms of depth, size and mining methods, and the possible interactions among the different mining processes, expose its facilities and processes to significant risk levels. Slope stability is one of the most critical sources of risk, at least in connection with surface operations. In order to cope with these risk conditions and to possibly mitigate them, new technological solutions based on process automation and innovative concepts have been adopted. This paper describes the innovative use of slope monitoring data currently under implementation at El Teniente, which is based on the combination of radar data used in an unconventional way and other geotechnical-geological analyses. Although slope monitoring radar is a well−established safety-critical monitoring practice designed to provide alarms in case of impending pit wall slope failures occurring, there is limited published information available on the use of such a powerful technology for other purposes in mining operations such as the interpretation of slope behaviour.
This paper presents the author’s experience with using radar data to identify the most likely failure mechanisms and to assess and validate geotechnical models. More specifically, at El Teniente the proposed integrated approach involves calibrating the input parameters for finite element modelling (FEM) to replicate movements observed through the monitoring data acquired by radar. The paper presents the results of the use of radar to monitor different areas of the mine affected by stability issues, such as the Camino Principal (the main access road to the Rajo Sur pit) and the north walls of the Rajo Sur (potentially affected by slope movements) and how the data have been used to get a better preliminary understanding of ongoing instability phenomena.
Slope Stability 2013 | Abstracts | 67
Slope monitoring and data visualisation state-of-the-art – advancing to Rio Tinto Iron Ore’s Mine of the Future™
P.J.H. de Graaf Rio Tinto Iron Ore, Australia
S.D.N. Wessels Rio Tinto Iron Ore, Australia
AbstractRio Tinto Iron Ore’s (RTIO) Western Australian mine operations comprises 14 mines with a
centralised ‘Mission Control’ Operations Centre (OC) in Perth, and currently delivers 237 Mt/a ore from over 120 individual open pits. Operational challenges in terms of implementation of effective slope monitoring systems with appropriate visibility of system health and alarm notifications needed to be addressed. The geotechnical, management and support teams are site and Perth based, and all require access to geoscience monitoring data.
Historically, each site had an independent monitoring and alarming systems. Transparency of monitoring data, health checks and alarming capabilities were limited. The lack of a system to display temporal geotechnical (slope performance), and hydrogeological monitoring data, with 24/7 alarm and system health status had been identified as a ‘gap’ following a previous slope instability incident at one of the Pilbara Operations.
At project inception, the need for a visualisation and management tool which had a multidisciplinary focus and integrating georeferenced geoscience monitoring data with physical models in near real time, was identified. Consequently the Geoscience Monitoring Data System (GMDS) was developed to address three main requirements:
• Provide a consolidated overview of all geoscience monitoring data and physical models.• Show monitoring system and device health, and alarm status at a high level.• Be integrated with existing slope performance and hazard management systems.This tool is in alignment with Rio Tinto’s Mine of the Future and RTIO’s Operations Centre
vision by using technology to reduce costs, increase efficiency and improve health, safety and environmental performance. It provides the functionality to manage diverse instrumentation data in a consistent, standardised approach to support RTIO’s geographically spread expansion plans.
Slope Stability 2013 | Abstracts | 68
Application of ground penetrating radar to identify the locations of sub-surface anomalies at Kansanshi Mine, Zambia
N.K. Smith First Quantum Minerals Ltd, Zambia
AbstractGeotechnical zones within the North West Pit and Main Pit of Kansanshi Mine consist
of a regolith profile with isolated marble blocks, referred to as ‘boulders’ within a highly weathered, unmineralised saprolite. The majority of the regolith is free-dig area with pre-split blasting to target boulders and create a smooth face. A serious rockfall risk is associated with irregularly-shaped boulders protruding from the batter face if not effectively treated during pre-splitting. Due to the random distribution of boulders within the regolith profile, drilling used a closely spaced pattern, with a large number of rigs, and this proved to be very costly. A ground probing radar system utilising a 50 MHz, unshielded, Rough Terrain Antenna (RTA) to scan a predetermined grid over a planned blast pattern, is able to detect subsurface anomalies such as boulders and cavities. Scan data can be imported into Surpac™ and manipulated to create a three dimensional boulder model from which an effective blast pattern could be designed.
Results have indicated several significant benefits; up to 80% cost saving in terms of drill and blast, more effective utilisation of drilling resources in hard rock areas, effective presplitting of boulders on highwall faces reducing rockfall risk and reduced equipment damage through identification of subsurface cavities.
Slope Stability 2013 | Abstracts | 69
Application of advanced InSAR techniques to detect vertical and horizontal displacements
J. Morgan TRE Canada Inc., Canada
S. Raval The University of New South Wales, Australia
B. Macdonald TRE Canada Inc., Canada
G. Falorni TRE Canada Inc., Canada
J. Iannacone University of Modena and Reggio Emilia, Italy
AbstractThe monitoring of surface subsidence is an important aspect in many underground mines.
There are various ground-based methods that can be used for deformation monitoring, including optical levelling, GPS, and tiltmeters. This study proposes the use of satellite-based InSAR for the monitoring of surface movement over the Metropolitan Mine, an underground coal mine located in the Southern Coalfields of New South Wales, Australia where ground subsidence has been documented. An advanced multi-image InSAR approach, characterised by a high density of measurement points and millimetre precision, is applied to illustrate how results provide an overview of surface displacement dynamics before, during and after active mining. Two stacks of ENVISAT radar imagery (87 total images) acquired between June 2006 and August 2010 were analysed with the SqueeSAR™ algorithm to reconstruct ground movement patterns during this period. Movements were assessed on a 35-day interval (the revisitation frequency of the ENVISAT satellite), and a time series of deformation was generated for every measurement point. The use of two image stacks acquired from different viewing geometries allowed both the vertical and east–west components of ground movement over this site to be determined. Results illustrate the surface-level impact of underground mining by quantifying the spatial extent and timing of surface movement. The precision of the InSAR data were briefly assessed by comparing results with ground-based GPS survey measurements. While the timing and direction of movements were similar, the comparison was limited by the lack of both spatial and temporal overlap of the data sets. The use of a radar satellite with a higher temporal frequency is recommended for future monitoring of this site.
Slope Stability 2013 | Abstracts | 70
Geotechnical risk management at Teck Coal
A. Bidwell Teck Coal Ltd., Canada
A. Knight Teck Coal Ltd., Canada
W.S. Anderson Teck Resources Ltd., Canada
AbstractThe first standardised Geotechnical Assessment Process for identifying and assessing
geotechnical risks at Teck Coal’s open pit mining operations was developed and implemented in 2012. This work was started as a corporate initiative because Teck, as a publicly traded company, desired to demonstrate industry-best practices for managing geotechnical risks and to develop Teck Coal corporate geotechnical standards. Furthermore, corporate geotechnical standards and a consistently high level of geotechnical practice are required as part of the safe and profitable execution of the potential expansions at Teck Coal’s operating sites and the possible development of additional mines.
This paper describes the three stage Geotechnical Assessment Process – the application of an assessment tool to scrutinise the geotechnical aspects of mine design, operation and closure, the categorisation and ranking of identified geotechnical risks, and the development of action plans to mitigate the risks. The assessment tool was developed in-house because there were no suitable published or publicly-available procedures. The risk categorisation and ranking procedure was adapted from the existing Teck stage gating process used for major projects. The ranked risks were grouped by common themes, and then used as the basis for developing site-specific ‘Project Initiatives’ that list actionable steps to ensure that each site’s geotechnical systems and processes are aligned with Teck Coal’s emerging standardised approach for identifying and managing the geotechnical risks at existing operations and for potential expansions.
Slope Stability 2013 | Abstracts | 71
Undrained behaviour in spoil piles
A. Duran Pells Sullivan Meynink, Australia
AbstractStability of spoil piles has been traditionally undertaken with the use of drained strength
parameters and utilising groundwater profiles within the spoil which are appropriate. Moreover, whilst the author’s experience suggests this is by far generally the case, review of recent failures at two strip mining operations suggests scenarios where there is a strong indication that undrained strength parameters could be assigned. The author presents seven case studies. As an alternative to undrained strength parameters, the author has considered; low strength shears in the sub-floor or spoil loading providing short term pore pressure increases in the sub-floor. The former provides unrealistic estimates of shear strengths applicable at both operations whilst the latter requires invoking groundwater assumptions, which although appearing reasonable, are difficult to readily implement in stability analyses.
Accepting that undrained behaviour is appropriate, based on the seven case studies this paper highlights three key aspects: scenarios where undrained strengths are developed; materials that are likely to allow development of undrained strengths; and typical values of undrained shear strength indicated by back−analysis.
Slope Stability 2013 | Abstracts | 72
Shear strength parameters for assessing geotechnical slope stability of open pit coal mine spoil based on laboratory tests
A.K. Kho School of Civil Engineering, The University of Queensland, Australia
D.J. Williams School of Civil Engineering, The University of Queensland, Australia
N. Kaneko School of Civil Engineering, The University of Queensland, Australia
N.J.W. Smith School of Civil Engineering, The University of Queensland, Australia
AbstractAs open pit coal mines venture to previously unchartered depths, the importance of ensuring
the geotechnical slope stability of high spoil piles becomes critical. However, a reasonable understanding of material parameters under the high stresses involved is yet to be achieved. Of particular interest is the necessity and effectiveness of testing scalped specimens in the laboratory and applying the results obtained to actual mine spoil piles. In an attempt to better understand the implications of particle size on shear strength parameters of coal mine spoil materials, samples were retrieved for testing from four mine sites in Queensland and New South Wales. The sampling covered a range of spoil types from fresh, well-cemented sandstone to weakly-cemented, weathered clay-rich rock. Laboratory direct shear strength testing was undertaken in shear boxes of two sizes; 60 and 300 mm, to investigate the effects of scalping. Specimens were placed loose and tested at their as-sampled moisture content and in a water bath. This was aimed at better simulating mine site conditions in which initially relatively dry spoil is placed loose and is subsequently wet-up by rainfall infiltration. The paper presents the shear strength parameters obtained for spoil specimens tested in the laboratory, and compares these with data from the literature and recommended shear strength parameters, which has implications for assessing the geotechnical slope stability of coal mine spoil piles.
Slope Stability 2013 | Abstracts | 73
Flow failure in coal stockpiles – how to reduce risk
P. Davies Golder Associates Pty Ltd, Australia
S. Zargarbashi Golder Associates Pty Ltd, Australia
L. McQueen Golder Associates Pty Ltd, Australia
AbstractThis paper presents findings from a geotechnical study undertaken to reduce the risk of coal
stockpile instability, following a flow failure observed in New South Wales. To characterise the stockpile behaviour, key input parameters such as permeability, shear strength and compressibility have been assessed for different in situ densities. Excess pore water pressure developed within the stockpile has been estimated by finite element analyses, using 2D PLAXIS, for different stockpile filling rates and target heights and taking into account the stockpile loading/unloading operations adopted in the mine. PLAXIS pore pressures were then incorporated into a series of limit equilibrium stability analyses conducted for three stockpile heights at different filling rates to study variation of Factor of Safety (FS) with the rate of stockpile filling rate, stockpile height and groundwater level. Conclusions from this modelling case study show that loading rates as high as 5 m/day may be adopted to raise the stockpile to a maximum height of about 10 m. Placement rates faster than 3 m/day result in an elevated risk of instability for higher stockpiles. Placement rates faster than 1 m/day increase the risk of flowslides for stockpiles of 15 m or higher. The analysis also shows that loader reclamation from the toe shortly after stockpile filling escalates the risk of instability for stockpiles above 10 m placed faster than 1 m/day. The results were used to update a mine stockpile risk management plan to include consideration of stockpile filling rates, coal placement/reclamation method and stockpile height. A monitoring strategy was also developed to assist with risk management.
Slope Stability 2013 | Abstracts | 74
Integration of full waveform terrestrial laser scanners into a slope monitoring system
A. Afana 3D Laser Mapping Ltd; and University of Durham, UK
G. Hunter 3D Laser Mapping Ltd, UK
J. Davis 3D Laser Mapping Ltd, UK
N.J. Rosser Department of Geography, Durham University, UK
R.J. Hardy Department of Geography, Durham University, UK
J.G. Williams Department of Geography, Durham University, UK
AbstractForecasting of the timing of slope failure has been widely modelled using strain-rate based
approaches. Such techniques are reliant upon high-precision data on slope deformation, yet conventionally a trade-off between monitoring precision and spatial resolution has to be made in mine slope safety systems. Newly available full waveform terrestrial laser scanners (FW-TLS) have been shown capable of capturing detailed additional metrics of rock slope surfaces, which from sequential scans allow significantly reduced uncertainties in change detection. Innovatively, this approach obtains both geometric and radiometric target surface information which is suited to the measurement of very small scale deformation, whilst retaining the spatially rich detail of TLS point-clouds.
We present data captured using this new technology integrated into the slope safety monitoring system ‘SiteMonitor’, to explore the opportunities offered by this new technology in characterising actively failing rock slopes in new ways. Results presented highlight the ability to resolve surface features at a scale appropriate to precursory mass wasting and creep in unstable rock slopes. These findings open the possibility for a step-change in the integration of recent strain-rate based predictive models with the unprecedented level of combined precision and detail offered by newly available FW-TLS data.
Slope Stability 2013 | Abstracts | 75
2011 Manawatu Gorge landslide-technical challenges faced during remediation
M.B. Avery Geovert Ltd, New Zealand
S. Bourke Geovert Ltd, New Zealand
AbstractThe August 2011 Manawatu Gorge landslide had an initial failure of approximately 20,000 m3.
The sheer volume of the failure caused the closure of State Highway 3 through the gorge and a rapid response team consisting of consulting engineering geologists and specialist contractors acted promptly to ascertain the extent, cause and short term remediation works to allow reopening of the very important transport link. In the following months several further failures occurred which led to the development and design of extensive long term remedial works. A design workshop was held in November where scientists, engineers and specialist contractors convened to discuss options for the long term remediation of the slip. The final design included the removal of some 370,000 m3. The extent of the earthworks was determined using the Digital Terrain Model (DTM) developed earlier in the project, based on a combination of Geological and Nuclear Sciences (GNS) produced 3D laser scans and recently flown LiDAR. The earthworks began in December 2011 and finished (down to road level) in May 2012. Once excavation was completed the highway required an almost complete rebuild as there were a number of half and full bridge structures that were extensively damaged during the event, likely both from the sudden impact energy of material during failures and also the long term effects from thousands of tons of material loading the structures over an extended 12 month period. Stabilisation and drilling work on site included the installation of mesh drape, horizontal shallow inclined drainage holes, stabilisation of colluvium slopes using rock dowels and installation of a 500 kJ Geobrugg rockfall attenuator. The stabilisation of the landslide and the rebuilding of the highway structures was completed in October 2012.
Slope Stability 2013 | Abstracts | 76
Mt Owen Mine barrier pillar
W.D. Bartlett Thiess Pty Ltd, Australia
I.H. Clark GEONET Consulting Group, Australia
D.E. McCormack Thiess Pty Ltd, Australia
G.D. Johnson Thiess Pty Ltd, Australia
A.N. Brown Thiess Pty Ltd, Australia
AbstractAs the Mt Owen Mine progressed, turning from mining in a south westerly direction to a
south easterly direction, in-pit dumping constraints demanded an innovative solution to prevent potential lowwall instabilities. An in situ rock pillar was designed to retain waste spoil, this was termed the ‘barrier pillar’. Measuring 270 m high and over a kilometre long, consisting of over 40 Mbcm of in situ rock and retaining in excess of 160 Mm3 of waste spoil. It is considered that the barrier pillar is the world’s largest in situ rock mass earth retaining structure.
Stability of the barrier pillar was governed by the weak tuffaceous layers within the coal that have caused historical instabilities. Analyses of the barrier pillar have been undertaken throughout the mine life; as the mine design evolved, so did the pillar design. The initial analysis was undertaken using a two-dimensional limit equilibrium model with multiple sections. Due to the complex nature of the geological structure, a subsequent analysis was undertaken using FLAC3D. Three pillar designs were analysed through thirteen stages of mining in order to predict rock mass behaviour through the proposed mining sequence, identify potential instability and determine the most appropriate pillar design.
Automated prism monitoring and two brands of slope stability radars were used to monitor displacement of the barrier pillar. No significant displacement was detected during mining prompted an investigation into maximising coal recovery. Two-dimensional limit equilibrium analysis was used to assess the design. Comparisons were made between the successfully mined goodbye cut and the original FLAC3D modelled pillars to ensure no additional modelling was required.
Slope Stability 2013 | Abstracts | 77
Quarry wall stability and design optimisation using photogrammetric mapping and analysis techniques
P.W. Booth Golder Associates Pty Ltd, Australia
G.E. Meyer Golder Associates Pty Ltd, Australia
AbstractA geotechnical assessment of the Oaklands Junction Quarry, Melbourne was undertaken
to provide recommendations on pit wall design parameters for use in future quarry planning. Holcim (Australia) Pty Ltd plans to double the depth of the existing main pit over the remaining life of the quarry, and a robust geotechnical assessment of the existing pit walls was required to provide long term pit face stability during operation and subsequent quarry rehabilitation.
Due to safety restrictions, access to the batters to undertake conventional (tape measure and compass) geotechnical mapping was very limited. The acquisition of geotechnical mapping data is described, using photogrammetric methods to undertake the mapping remotely. Measurements included the orientation, spacing, persistence and large scale waviness of the rock discontinuities that control the stability of the quarry pit walls.
The use of photogrammetry provided far greater mapping coverage and a much larger set of high quality geotechnical data than could have been obtained by conventional mapping methods. The persistence and large scale waviness of the discontinuities are critical to the geotechnical design, due to the typically low shear strength of joint infill materials.
The acquisition of high resolution digital terrain models (DTMs) of the quarry batter faces is described, generated using the 3DM Analyst Mine Mapping Suite (ADAM Technology, 2013) digital photogrammetry system from ‘stereo pairs’ of photographs taken of the pit walls. The same software was then used to carry out the remote geotechnical mapping. The results included more than 1,200 individual measurements of discontinuity orientation, as well as a smaller number of measurements of discontinuity spacing and persistence.
The DTMs were used to quantitatively assess the large scale waviness of selected discontinuities, and provided justification to increase the large scale friction angle adopted for the subsequent stability analyses by up to 5°, as compared to the values that would otherwise have been adopted based on drill core alone. The assessment of safe pit slope angles is discussed, and observations of existing large scale failures in the pit walls were used to corroborate the use of increased friction angle in the design.
Slope Stability 2013 | Abstracts | 78
Early detection of impending slope failure in open pit mines using spatial and temporal analysis of real aperture radar measurements
G.J. Dick Department of Earth and Ocean Sciences, University of British Columbia, Canada
E. Eberhardt Department of Earth and Ocean Sciences, University of British Columbia, Canada
D. Stead Department of Earth Sciences, Simon Fraser University, Canada
N.D. Rose Piteau Associates Engineering Ltd., Canada
AbstractSlope monitoring in open pit mines is an essential component of day-to-day operations and
plays a key role in assisting geotechnical engineers and mine operators in maintaining mine safety and production schedules. Pit slope monitoring techniques have advanced significantly within the past decade, most notably in ground-based radar technology. Ground-based radar allows real-time monitoring of slope deformation across a broad coverage area, alerting mine staff to wall movements exceeding established thresholds. Line of-sight measurements derived from the radar can be presented as 3D point clouds for the scan area, allowing mine staff to view the distribution of slope movements across the pit wall with each progressive scan.
This paper presents a new methodology for spatial and temporal analysis of deformation point clouds captured by ground-based radar. The methodology builds on two existing early warning methods, the Fukuzono inverse-velocity method and the SLOpe gradient (SLO) method, which are based on the analysis of point measurement data derived from traditional geodetic prism monitoring. However, similar methodologies that fully utilise the spatial and temporal characteristics of ground-based radar data are yet to be developed.
Radar data from historical slope failures captured by GroundProbe Slope Stability Radar (SSR) at a number of hard rock mines was utilised in the development of the new spatial and temporal analysis methodology. A slope failure that occurred at an open pit copper mine is presented throughout as a case example. The spatial analysis component of the methodology uses a benchmark point (or pixel), based on an alarm threshold specific to each failure case, and averaged deformation increments based on a percentage of the deformation measured by the benchmark pixel at the time of alarm. The temporal analysis component of the methodology examines deformation and velocity trends for all spatial analysis cases. The results of the spatial and temporal analysis were then used to evaluate the inverse-velocity and SLO time of failure prediction methods. Overall, the proposed methodology will improve, and provide a more systematic means of interpreting spatial and temporal ground-based radar data, aiding geotechnical engineers in managing slope movement alarms and alarm responses to provide a safer working environment for mine employees.
Slope Stability 2013 | Abstracts | 79
Geohazard mitigation in remote and rugged terrain
U.K. Gunasekera Rio Tinto, Australia (formerly with Newmont Asia Pacific Region)
AbstractNewmont Asia Pacific Region (APAC) operated a number of exploration tenements in Papua
New Guinea, the Solomon Islands and Indonesia. A common feature to all these sites were rugged terrain, very thick vegetation canopy, high intensity rainfall and relatively young geology. Geohazards such as landslides, earthquakes and flash flooding are common in these terrains. Past incidents at the exploration sites highlighted the requirement for geotechnical input prior to site selection. This article explains the process that was developed in the preparation of a Geohazard Mitigation Tool (GHMT) that was used for the selection of safe sites suitable for Newmont exploration infrastructure. Available good quality topographic images were used to acquire slope, drainage and landslide information. Regional and local soils and geology maps were helpful in ascertaining soils conditions. Prevailing wind information was also useful. To put all the above information together into a geohazard rated map of the exploration regions, ArcGIS tools were utilised.
Slope Stability 2013 | Abstracts | 80
Stabilisation of landslides using gravity fed siphon and electro-pneumatic pumped wells: two examples of slope stabilisation projects from the United Kingdom and Czech Republic
J.K. Holliday Aurecon Australia Pty Ltd, Australia (formerly High Point Rendel, UK)
A.R. Clark Independent consultant, UK (formerly High Point Rendel, UK)
D.S. Fort Atkins, UK (formerly High Point Rendel, UK)
A. Gillarduzzi High Point Rendel, UK
S. Bomont TPGEO, France
AbstractThe rise of groundwater in response to extreme weather events is having a major impact on
slope stability and the consequential disruption to infrastructure services and associated costs related to their repair is significant.
Climate change studies are predicting increased frequency and duration of extreme weather events. Case histories have demonstrated the link between prolonged rainfall events, rising groundwater levels and increased frequency of slope instability.
The stability of slopes can be improved if groundwater can be controlled and this is most commonly achieved through the use of drainage measures. An innovative drainage system that uses siphon drain and electro-pneumatic pump technology has been employed in Europe since 1986 using drains and lines of wells to lower and maintain groundwater levels within slopes.
Two examples of projects using siphon and electro-pneumatic drains to control slope stability are presented. The first example is a coast protection scheme constructed in 2004 at Castlehaven on the Isle of Wight in the United Kingdom. The second example involves landslide problems affecting remediation works to slopes undertaken in 2009 at a former open cast brown coal mine at the Most Ležáky site in the Czech Republic.
Slope Stability 2013 | Abstracts | 81
Risk management and remediation of the north wall slip, West Angelas Mine, Western Australia
G.G. Joass Rio Tinto Iron Ore, Australia
R. Dixon Rio Tinto Iron Ore, Australia
T. Sikma Rio Tinto Iron Ore, Australia
S.D.N. Wessels Rio Tinto Iron Ore, Australia
J. Lapwood Rio Tinto Iron Ore, Australia
P.J.H. de Graaf Rio Tinto Iron Ore, Australia
AbstractA planar failure of approximately 600 kT occurred on the north wall of Centre Pit North (CEPN)
at West Angelas Mine site in February 2010. The failure impacted a substantial resource of high grade iron ore and left a number of significant geotechnical hazards on and adjacent to the failure surface. These presented a series of challenges which had to be overcome in order to remediate the failure and reclaim the bulk of the buried ore. A number of recovery options were investigated and presented to management. This paper outlines the plan which was adopted, the challenges encountered during its implementation and the risk management and mining procedures used to bring the remediation and recovery to a successful conclusion.
Slope Stability 2013 | Abstracts | 82
Application of radar monitoring at Savage River Mine, Tasmania
G.K. Macqueen Grange Resources (Tasmania) Pty Ltd, Australia
E.I. Salas Grange Resources (Tasmania) Pty Ltd, Australia
B.J. Hutchison Grange Resources (Tasmania) Pty Ltd, Australia
AbstractGrange Resources Ltd have been utilising radar monitoring since 2007 at their Savage River
mining operation in Tasmania, Australia. Radar has provided prior warning of several large wall failures in the brittle amphibolite of the North Pit’s east wall, and these experiences have increased the confidence in the radar’s capability to provide reliable prior warning of large wall failures. With the increased confidence in the radar attention has focused on the remaining sources of risk in the forms of human error through mistakes in the application of the radar and human error in the form of ‘slips and trips’, particularly within software settings. These potential sources of human error are mitigated with the use of Standard Operating Procedures, Trigger Action Response Plans, training and checklists.
Radar monitoring of the east wall of North Pit has been found to have limited capability in providing prior warning of small wall failures. In order to mitigate the risk posed by small wall failures, remote controlled mining capabilities (including remote drilling, dozing, excavating, and blasthole loading) have been adopted for routine use within specified zones at the toe of the pit wall.
This paper describes how through applying appropriate radar alert thresholds across the entire pit wall, whilst ensuring the integrity of the radar monitoring system, and mitigating the risk posed by small wall failures, the risks of operating beneath a hazardous pit wall can be significantly reduced.
Slope Stability 2013 | Abstracts | 83
Slope stability study in open pit and underground mines by means of forensic analysis and radar interferometry
O. Mora Altamira Information, Spain
I. Álvarez Universidad de Oviedo, Spain
E. Amor Herrera Hullera Vasco-Leonesa, Spain
AbstractThis paper demonstrates the capabilities of satellite radar technology to generate complete
ground deformation maps of an open pit mine, to follow and detect movement intensities ranging from millimetric to metric scales. Several vulnerable parts of the mine have been studied and monitoring of these very small to very large instabilities has provided valuable information for risk and exploitation management at the mine. A forensic analysis has been also performed and validated with these interferometric radar measurements.
Images from the X-band high resolution images of TerraSAR-X satellite have been acquired between 2008 and 2012 to monitor ground displacement evolution. Two types of ground markers, natural reflectors providing backscattering of the terrain and trihedral artificial reflectors installed on certain areas of the mine have been used. Measurement quality depends on the temporal changes, and several radar Interferometric techniques, including persistent scatterer interferometry (PSI) and Altamira Information developments (stable point network and non-coherent technique) have been used to detect displacement intensities. Phenomena caused by mine activities have been detected, showing a perfect temporal correlation with the mine evolution. The project has also been very useful for the control and analysis of a strong slope instability affecting the open pit, where displacements have been more than 10 m in some months.
Slope Stability 2013 | Abstracts | 84
Stability analysis and remedial design of two road cuttings in North Queensland based on remote geotechnical mapping using digital photogrammetry
I. Ortega Golder Associates Pty Ltd, Australia
P.W. Booth Golder Associates Pty Ltd, Australia
J. Darras Golder Associates Pty Ltd, Australia
AbstractRemote geotechnical mapping of two large rock cuttings on a vital transportation corridor
in North Queensland was undertaken to provide input data for stability analysis and design of stabilisation elements. The mapping approach described utilised state-of-the-art digital photogrammetry tools to allow the collection of structural data from large areas where direct access to the slopes for conventional (tape measure and compass) mapping was either not possible or very limited without the use of rope access methods.
The photogrammetric method employed allowed the mapping to be completed rapidly and safely, without affecting the serviceability of the roadway during the site investigation. It provided measurements of the orientation, spacing and persistence of the rock discontinuities that control the stability of the cuttings. It also provided detailed digital terrain models (DTMs) of the slopes, which provided critical topographic information for input to the analysis and design processes.
In recent years, the use of digital photogrammetry as a tool to collect structural and geotechnical mapping data from large rock cuttings has become commonplace in the mining industry. The application of this method to civil engineering problems on the other hand has been far less common, but comes as a natural progression as this technology becomes more user-friendly and cost-effective.
Slope Stability 2013 | Abstracts | 85
Hangingwall and footwall slope stability issues in sublevel caving
B-M. Stöckel Luossavaara-Kirunavaara AB, Sweden
K. Mäkitaavola Luossavaara-Kirunavaara AB, Sweden
J. Sjöberg Itasca Consultants AB, Sweden
AbstractMining using large scale underground sublevel caving results in caving of the surrounding
host rock and mining-induced ground surface deformations. These effects are most prominent on the hangingwall side, but also develop to some extent on the footwall side of an orebody mined with caving methods. This situation is, in many respects, similar to that of large scale slopes, albeit with the addition of the caved rock. The problem issues are particularly similar for the case when underground mining commences below an existing open pit. The Luossavaara-Kirunavaara AB (LKAB) Kiruna Mine is a case in point, in which underground sublevel caving commenced in the 1960s, following open pit mining that had been on-going since the late 19th century. The mine is in close proximity to the city of Kiruna, which has resulted in a continuous urban transformation of the Kiruna municipality for almost a century. The LKAB industrial area is also strongly affected. With deepened mining, the effects on the ground surface are becoming larger and the demands on monitoring and prediction are larger than ever today. This paper presents a status report concerning large scale slope stability in cave mining and the effects on the surroundings, including currently on-going rock mechanical activities within this subject area. Ground deformations are currently being monitored using Global Positioning System (GPS) techniques on fixed measurement hubs, with measurements taken quarterly of strategically important hubs and annually on all installed hubs (today around 450). LKAB has an on-going research and development project on the use of radar remote sensing (InSAR techniques) for ground deformation monitoring. The advantages of the InSAR techniques are that: (i) measurements have high spatial density, (ii) monitoring occurs more frequently with reduced manpower (currently every 24th day with the Radarsat-2 satellite), and (iii) the need of fixed measurement hubs is eliminated. The theoretical precision is very high but there are issues regarding measurements at high latitudes (snow-covered ground, etc.), which are currently being investigated. The paper also describes the methodology used for predicting ground surface deformations due to mining. Prognoses are produced for planning purposes – both for internal (within LKAB) and external (the municipality of Kiruna, etc.) use. The prognosis methodology employed is based on a combination of analysis of measurement data, numerical modelling, and empirical relations. The resulting prognoses are reviewed annually and updated as required. With the anticipated increase in affected surface area, the precision in prediction needs improvement and LKAB is sponsoring a number of research projects concerning both hangingwall and footwall stability, which are briefly described in the paper.
Slope Stability 2013 | Abstracts | 86
An evaluation of the CUSUM and inverse velocity methods of failure prediction based on two open pit instabilities in the Pilbara
J. Venter Rio Tinto Iron Ore, Australia
A. Kuzmanovic Rio Tinto Iron Ore, Australia
S.D.N. Wessels Rio Tinto Iron Ore, Australia
AbstractPredicting the expected time of slope collapse is an important aspect of managing open pit
slope stability as it determines the appropriate actions to be taken. It is important to know when to evacuate but is also useful to know well in advance if a particular slope is creeping towards collapse or whether the deformations measured are unlikely to result in collapse. Having this type of information well in advance allows a mine to plan and execute remedial actions, such as schedule changes, slope angle changes and buttresses, that will mitigate economic as well as safety risks. While several methods of analysing slope monitoring data have been published to date, none have been able to establish themselves as the definite answer to any of these questions.
This paper evaluates several previously published methods of predicting the time of slope collapse based on the monitoring data collected for slope instabilities that occurred at two of Rio Tinto’s Pilbara Iron Ore operations in 2009 and 2010. The methods tested against the data are: CUSUM, inverse velocity and the slope of velocity and time multiplied velocity (SLO) method (Mufundirwa and Fujii, 2008). The paper concludes by evaluating the effectiveness of each of these methods to serve as early warning of impending failure and to predict the onset of collapse.
Both instabilities were managed without injury to personnel and no loss of equipment.
Slope Stability 2013 | Abstracts | 87
Slope stabilisation program at West Gully, PT Freeport Indonesia
E. Widijanto PT Freeport Indonesia, Indonesia
I. Setiawan PT Freeport Indonesia, Indonesia
K. Afrizal PT Freeport Indonesia, Indonesia
M. Stawski PT Freeport Indonesia, Indonesia
P. Warren PT Freeport Indonesia, Indonesia
B. Utama PT Freeport Indonesia, Indonesia
AbstractPT Freeport Indonesia operates a copper-gold mine located in the province of Papua, Indonesia,
about 3,500 km east of Jakarta. Current ore production from the project is about 220,000 tonnes per day (tpd) of which about 2.5 ktpd from Big Gossan stope mine, 60 ktpd come from the DOZ block cave and the rest is mined from the Grasberg open pit. Two new underground mines under development are the Grasberg block cave and Deep Mill level zone to ultimately replace surface mine operation.
One of the critical zones for entire mining operation is the mill-processing area. This area is not only dedicated for the processing plant but also is used as access to one of underground waste dump areas. The mill area is surrounded by steep natural slopes and extreme topography which often results in instabilities (debris flows, rockfalls) related to the geological features. West Gully is one of locations at the mill area which requires extensive work to mitigate rockfall hazard which impacts on the operations at the mill. Historical rockfall incidents, geological information, site observation, rockfall simulation, and road access reliability requirement for the future mining operation drive geotechnical recommendations to provide robust rockfall mitigation option. Scaling and meshing of more than 7,000 m2, constructing two × 8,000 kJ of debris flow barriers, and 8,000 kJ of rock fence for an approximately 700 m high slope was required to reduce rockfall risk to an acceptable level. Those rockfall protections are augmented by 225 m corrugated steel tunnel at the mill level as an additional road protection from potential rockfall events.
Complex geological conditions, steep mountainous topography, average annual rainfall of 5,000 mm, foggy conditions, limited working space and the short distance to the critical facilities created a challenging situation for engineering design, construction, geotechnical monitoring and logistics. This paper outlines the slope stabilisation challenges and unique conditions and also the efforts of the team to reduce and mitigate rockfall hazards to ensure the safety of the workers and future safe production continuity.
Hydrogeology
Slope Stability 2013 | Abstracts | 89
Integrating complex hydrogeological and geotechnical models – a discussion of methods and issues
G. Fagerlund SRK Consulting (Canada) Inc., Canada
M. Royle Schlumberger Ltd., Canada
J. Scibek SRK Consulting (Canada) Inc., Canada
AbstractPrediction of pore pressure data used in complex 3D geotechnical slope stability modelling
often runs into problems associated with dissimilar model domains, grids, nodal density, etc. This is often due to the larger scale hydrogeological model being restricted to the use of laterally extensive layers to represent the site lithology, whereas the geotechnical models often use a cubic or tetrahedral convex blocking method for model construction. Hydrogeological model platforms do not always allow the modeller to reproduce the geology (especially if steeply dipping, over turned, or pinching out) or the slope details to the level of detail expected for the stability modelling.
To alleviate this problem, the use of regular sized elements in horizontal to moderately variable layers/slices is described. The model geometry is not new, but presented here as a means of solving some common problems encountered in pit design modelling. The resulting efficiencies in model construction, ability to modify the geology and pit wall design during the modelling process, and more accurately simulate a complex 3D problem in the hydrogeological model simulation are discussed. Methods for simulating drainage tunnels, drill hole fans, and horizontal drains using ‘discrete elements’ are presented. Additionally, the problems encountered with using larger scale (mine scale) models to determine boundary conditions for the smaller, pit wall scale models are discussed, with several methods for dealing with this reviewed.
This paper describes methods used to construct a FEFLOW® (DHI-WASY GmbH, 2012) finite element model of the West Wall 3DEC® (Itasca, 2013) stability analysis for the Ok Tedi mine life extension (MLE) that overcame some of these issues. However, the methods used are not limited to FEFLOW® or even Finite Element models, and are used with other codes that the hydrogeological modellers are familiar with. The paper does not presume to be a comprehensive examination of the methods and issues, rather to provide useful tips and discussion points for the slope stability modelling audience. As such, recognised limitations of the methods are included, and the authors invite readers to use this as a means to initiate further consideration of the modelling issues involved in the increasingly complex stability analyses taking place these days.
Slope Stability 2013 | Abstracts | 90
Three-dimensional pore pressure prediction in dual phase conditions for slope stability assessment
E.R. De Sousa Pells Sullivan Meynink, Australia
M.J. Fowler Pells Sullivan Meynink, Australia
G.E. Swarbrick Pells Sullivan Meynink, Australia
AbstractThis paper presents an approach for modelling both liquid and steam pore pressures for
prediction of slope stability of proposed mine slopes at the Lihir gold mine in Papua New Guinea.A three-dimensional FEFLOW model has been developed of the Louise Amphitheatre including
a centrally located geothermal zone. The model comprises a detailed lithological representation and some structural zones. The complex interaction of surface infiltration, ocean boundaries, geothermal upflow, dewatering, drainage to existing pits and groundwater and steam relief are represented in the model. The model is calibrated by some 200 vibrating wire piezometers that measure both pressure and temperature.
The model predicts both groundwater flow and heat transport for annual pit development. A unique post processing method has been developed to rapidly estimate steam pressures based on the flow and heat predictions. A detailed model assessment process has been developed in order to judge the reliability or otherwise of modelling output.
The output of the process is a three-dimensional pore pressure grid that identifies zones of both liquid and steam pressures. The results can be subsequently viewed or utilised elsewhere, such as inputs for slope stability analyses. Comparison with conventional dual phase modelling using TOUGH2 is favourable.
Stability analyses are used to confirm slope designs and target locations and times where steam relief is required.
Slope Stability 2013 | Abstracts | 91
Mine design for below water table clay detritals mining: Marandoo Mine, Western Australia
D. McInnes Golder Associates Pty Ltd, Australia
C. Haberfield Golder Associates Pty Ltd, Australia
P.J.H. de Graaf Rio Tinto Iron Ore, Australia
C. Colley Golder Associates Pty Ltd, Australia
AbstractGeotechnical investigations were carried out as part of the Feasibility Study Extension (FSE)
and Trial Mining program for the development of below the water table (BWT) expansion at Rio Tinto Iron Ore’s (RTIO’s) Marandoo Mine. The Marandoo Mine site is located in the Pilbara region of Western Australia, 1,500 kilometres north of Perth.
Previous studies have indicated that a 40 m thick, at approximately 40 m depth, layer of Tertiary clay, will present significant challenges relating to slope and waste dump design as well as operational challenges (trafficability and handleability). Due to uncertainty over the confidence of parameters derived from triple tube sampling and testing, conservative design parameters were adopted for the previous studies. It was recognised that significant upside could be realised through improved material characterisation techniques.
The main objectives of the investigation and testing program were to: 1) characterise the physical properties and variability of the clay; and 2) obtain design parameters for the slopes for mining of the pit. This was carried out with conventional drilling, sampling and logging procedures. Hyperspectral scanning of diamond core was undertaken, which provided useful information on the vertical distribution of clay species through the detrital stratigraphy. Following review of the historic sample test results, it was hypothesised that sampling and testing methods had contributed to pre-softening of samples. Subsequent testing focused on Shelby tube and in situ testing; both resulted in significant improvement in measured shear strength parameters over triple tube sampling.
A self-boring pressuremeter was used in two locations to carry out in situ testing of the clay at various depths. The results of the pressuremeter testing have indicated that the permeability of the clay is significantly lower than assumed in previous studies. An assessment of the effect of the structure of the clay on the stability of the slopes will be an objective of further studies.
Key outcomes so far have emphasised the significant impact of sampling method, preservation, timely testing on derived material properties, and recognition of the limitations of various techniques in characterising heavily over consolidated clays. The material characterisation has also confirmed the critical importance of water management in mining in relation to preserving clay strength. This work has enabled detailed planning to be undertaken for studies covering trafficability, handleabilty, waste dump and slope performance; with field trials scheduled in the mine plan.
Slope Stability 2013 | Abstracts | 92
The hydro-geotechnical decision cycle – having mine design and planning decisions made by the right people
J.W. Hall RPS Aquaterra, Australia
AbstractThe design of pit slopes where groundwater or pore pressure has some influence on slope
stability requires two key mining disciplines to be applied; geotechnical engineering and hydrogeology. These two broad disciplines also cover structural geology, geomechanical, groundwater and hydro-mechanical coupled modelling and surface water hydrology. These are all specialist disciplines with specific education and training requirements. With experience, we develop an understanding of, and can even become experts in, these other disciplines. That is, we become adept practitioners in the overall slope design and mine planning process. However, this takes time.
What of our site based mine planning staff, who are mostly young and still developing their overall mine planning skills? It is not uncommon for our site based geotechnical engineer (or hydrogeologist) to have a whole range of duties assigned to them, many of which are outside their current skill and experience levels. Is this fair? Can it result in practical, cost effective or safe slope designs? It can, but only when our site staff are provided with adequate technical support from the cross disciplines.
So, what does this support look like, and when do we need to provide it? A useful way to assess this is to consider what I call the Hydro-Geotechnical Decision Cycle. This is simple process whereby the geotechnical engineers does what they are good at (and qualified to do) and the hydrogeologists do the same, so that together they can develop the appropriate mine planning solutions through an iterative process of data collection, analysis, design, implementation and feedback. Sound familiar? This is the same as a Continuous Improvement cycle (i.e. plan-do-check-act).
This paper develops the concept of the Hydro-Geotechnical Decision Cycle and presents examples of where it can help when applied and where it has gone wrong when it has not been applied.
Slope Stability 2013 | Abstracts | 93
The hydrogeology of a moving cut slope and real time modelling of groundwater movement
I. Gray Sigra Pty Ltd, Australia
J. Wood Sigra Pty Ltd, Australia
B. Neels Sigra Pty Ltd, Australia
A. O’Brien Sigra Pty Ltd, Australia
AbstractThis paper covers the work undertaken to determine the behaviour of groundwater in a
moving cut slope comprising fractured igneous rock overlying sedimentary deposits. The work was undertaken to provide part of a solution to the stabilisation of the slope through drainage. The work initially involved the installation of multiple piezometers and several pumping tests to determine the hydraulic conductivity and storage characteristics of the rock mass. Using this information a numerical model of the slope was created in which the time variant input was the piezometric head. Using the values of hydraulic conductivity and storage along with the varying piezometric information it was possible to determine where water was entering and leaving the slope during different weather events and to therefore optimise drainage design. The paper also describes the data acquisition and telemetry system developed and employed on this project and also some of the mathematics of drainage design. The paper also considers some drainage solutions to stabilise the slope more effectively than the cut and fill approach that has not yet succeeded.
Rockfall
Slope Stability 2013 | Abstracts | 95
An integrated approach for rockfall analysis with drapery systems
K. Thoeni Centre for Geotechnical and Materials Modelling, The University of Newcastle, Australia
C. Lambert Civil and Natural Resources Engineering, University of Canterbury, New Zealand
A. Giacomini Centre for Geotechnical and Materials Modelling, The University of Newcastle, Australia
S.W. Sloan Centre of Excellence for Geotechnical Science and Engineering; and Centre for Geotechnical and Materials Modelling, The University of Newcastle, Australia
J.P. Carter Centre of Excellence for Geotechnical Science and Engineering; and Centre for Geotechnical and Materials Modelling, The University of Newcastle, Australia
AbstractThe rockfall hazard in mining environments needs to be rigorously managed in order to ensure
safe mining operations, in particular when designing portal entries for punch longwalls. The installation of drapery systems is a common practice to mitigate the rockfall hazard at the base of highwalls. However, the hazard is not completely eliminated since blocks can still detach and fall in between the drapery and the highwall. This contribution shows how geostructural modelling and 3D rockfall analysis can be combined in order to accurately map and assess the rockfall hazard at the base of such highwalls. The study entails the estimation of the size distribution of unstable blocks and the simulation of their trajectories and velocities for highwalls without and with drapery.
First, 3D photogrammetry is combined with discrete fracture network modelling in order to generate polyhedral models of the rock mass structure. Polyhedral modelling and kinematic analyses are combined to estimate the volume and shape distribution of unstable blocks. Unstable blocks are then classified according their shape.
Second, a 3D discrete element rockfall model is presented which allows for an accurate prediction of velocities and run-out distances for rock slopes with and without drapery. The 3D model is used to predict trajectories and velocities for blocks representative of a highwall, i.e. block size and shape according the results from the polyhedral modelling. The focus is to investigate the efficiency of the drapery and to quantify the residual rockfall hazard at the base of a highwall.
Slope Stability 2013 | Abstracts | 96
Coefficient of restitution for rigid body dynamics modelling from onsite experimental data
F.R.P. Basson Newmont Asia Pacific, Australia
R. Humphreys Newmont Asia Pacific, Australia
A. Temmu Newmont Asia Pacific, Australia
AbstractRigid body dynamics uses the Newtonian laws of motion to solve the physics behaviour of
moving bodies as a function of time. This approach is fast enough for real time simulation of multiple fall bodies, and can simulate the trajectories of three-dimensional volumetric bodies during free fall, bouncing, sliding and rolling. An additional benefit of rigid body dynamics is that the input parameters required are few, measurable and intuitive, as only the coefficient of restitution (COR), and the static and dynamic friction angles are required.
The Geotechnical Team at Newmont Boddington Gold (Boddington) undertook simple experiments to determine the ranges of COR values applicable to different surfaces for the Boddington pits. Ten rocks between 0.35 and 2.08 kg were collected, weighed, marked, and measured. Each rock was then dropped ten times from a height of 1.40 m onto the four different horizontal pit surfaces ‘pit floor’, ‘haul road’, ‘catch berm’, and ‘hard rock’. The rebound of each drop test was measured with a scaled white board behind the test area from video footage. A total of 400 data points were collected and the results analysed. It was found that the different rebound surfaces have different levels of predictability in rebound behaviour, and that some surfaces a more prone to occasional outlier results. The aim of these experiments was to obtain rebound information for use in the rigid body dynamics modelling software package Trajec3D.
During a full scale rockfall experiment, and the accompanying three dimensional back analysis with volumetric fall bodies, many factors determine the outcome that complicates the verification of the individual simulation components. The simple experiments discussed before were simulated in Trajec3D to determine if rigid body dynamics could simulate realistic rebound behaviour with different rock shapes, sizes, and physics material interaction properties.
The combined outcomes from the rockfall experiments and rigid body dynamic simulations lead to the identification of the critical factors controlling fall body rebound behaviour at Boddington. Appropriate COR values will be selected and used in the analysis of larger scale rockfall experiments, the back analyses of known rockfall events, and to identify and assess potential future rockfall areas.
Slope Stability 2013 | Abstracts | 97
Spatial and temporal aspects of slope hazards along a railroad corridor in the Canadian Cordillera
R. Macciotta Department of Civil and Environmental Engineering, University of Alberta, Canada
D.M. Cruden Department of Civil and Environmental Engineering, University of Alberta, Canada
C.D. Martin Department of Civil and Environmental Engineering, University of Alberta, Canada
N.R. Morgenstern Department of Civil and Environmental Engineering, University of Alberta, Canada
M. Petrov Department of Civil and Environmental Engineering, University of Alberta, Canada
AbstractA successful slope management program depends on understanding the interaction between
the potential slope failure and the elements at risk. This interaction defines the magnitude and likelihood of the potential consequences, which in turn defines the need for allocating resources for risk mitigation. The interaction can be divided into the probability of interaction between the displaced material and the elements at risk, and the degree of loss should impact occur. In this paper, the temporal and spatial aspects of landslides are analysed along a section of a railroad corridor through the Canadian Cordillera. The temporal and spatial aspects of the elements at risk are discussed and illustrated within the context of railroad freight train operations. An example is presented where the annual frequency of interaction between landslides and freight trains is estimated, and the associated spatial and temporal variability analysed. The paper highlights the importance, within a slope risk management strategy, of understanding landslide trends in space and time and how these spatial and temporal trends are related to morphology, geology and triggering mechanisms.
Slope Stability 2013 | Abstracts | 98
Earthquake stability assessment for open pit mine slopes
J.C.W. Toh Pells Sullivan Meynink, Australia
D.K.E. Green Pells Sullivan Meynink, Australia
G.E. Swarbrick Pells Sullivan Meynink, Australia
M.J. Fowler Pells Sullivan Meynink, Australia
B.E. Estrada Pells Sullivan Meynink, Australia
AbstractEarthquake stability assessment of large open pit mine slopes brings together two areas of
slope engineering that are usually quite separate. To account for the scale and nature of open pit slopes, analysis techniques widely used for small scale civil infrastructure slopes need to be adapted and then extended.
The first part of this paper presents a framework for earthquake stability assessment of open pit mine slopes that has been used in practice by the authors. The framework attempts to provide consistency across various analysis techniques, from pseudo-static analysis to dynamic numerical modelling. Guidance is given for selecting an appropriate earthquake load coefficient for pseudo-static analysis.
The second part of this paper presents two examples of dynamic numerical modelling. One example demonstrates that the earthquake response of large rock slopes is highly dependent on the interaction between the seismic hazard, the resonant behaviour of the slope and surrounding ground, the rock mass character, and the slope geometry, and it follows that understanding dynamic site response is an integral part of earthquake engineering for large rock slopes. The other example presents parts of a detailed analysis of slope stability and deformation, and compares the results to those obtained from simpler analysis methods.
Slope Stability 2013 | Abstracts | 99
Seismic stability of large open pit slopes and pseudo static analysis
B. Damjanac Itasca Consulting Group, Inc., USA
Varun Itasca Consulting Group, Inc., USA
L. Lorig Itasca Consulting Group, Inc., USA
AbstractSeismic shaking induces stress changes in rock and soil slopes, which when combined with
existing static stresses, may exceed the available strength and cause failure. Although one of the greatest hazards during strong earthquakes is associated with consequences of triggered landslides and natural slope failures, existing data seem to indicate that earthquakes are not a credible stability hazard for open pit slopes. Because regulations require investigation of slope stability under earthquake loading, relatively simple quasi-static analyses are typically carried out. The quasi-static analysis of the effect of seismic shaking on stability of slopes is usually too conservative. Thus, the mines primarily rely on empirical evidence when considering seismic hazard in the design of the open pit slopes. However, it is important to understand the reasons for relatively good performance of open pit slopes compared to multiple evidences of landslides during historical earthquakes, but also to determine, using a proper methodology, the conditions when open pit slope stability can be at risk during seismic shaking.
This paper provides, based on mechanical principles (using numerical models), a rationale to explain field observations that indicate relatively small effect of earthquakes on stability of open pit slopes, and also investigates the level of conservatism in the predictions of the quasi-static analyses as a function of important ground motion parameters. First, the increased demand in terms of dynamic stresses is quantified as a function of pit/slope geometry (topographic amplification) and amplification by wave trapping due to difference in stiffness of geological layers. It is shown that open pits have an advantage due to their three dimensional circular/elliptical geometry and less amount of weathered material close to the surface as compared to natural slopes. Next, a typical slope is subjected to suite of ground motions covering a wide range of peak ground accelerations and frequency contents. The dynamic Factor of Safety is calculated based on displacement criteria. After comparing the reduction in dynamic Factor of Safety with different earthquake intensity parameters, peak ground velocity (PGV) appears to be the parameter that best correlates with seismic risk for slopes. Finally, it is shown that the conventional approach of pseudo−static analysis using earthquake-magnitude-based seismic coefficients results in Factors of Safety that are almost always conservative, and often too conservative.
Slope Stability 2013 | Abstracts | 100
Three-dimensional rockfall modelling and rockfall protection – Port Hills
M.B. Avery Geovert Ltd, New Zealand
H. Salzmann Freefall ZT GmbH, Austria
A. Teen Geovert Global Pte Ltd, Singapore
AbstractAfter the February 2011 Christchurch earthquakes Geovert were commissioned by the
Canterbury Earthquake Recovery Authority (CERA) to provide the desperately needed answers to the widespread rockfall hazard. Including how best to protect people and assets, how much will it cost and how long will it take. To provide this information Geovert proposed the use of a newly developed state of the art 3D rockfall modelling program which was capable of modelling the vast earthquake affected area in the Christchurch Port Hills. The modelling focused on possible remedial options and their costs, and associated construction programmes, to provide supplementary information to the current Christchurch City Council (CCC) commissioned Geological and Nuclear Sciences (GNS) reports. The outcomes of the modelling were to assist CERA in making critical decisions relating to areas where rockfall hazard exists and where protective works may effectively reduce the this hazard. The 3D modelling was carried by a subconsultant to Geovert Ltd using Hy-Stone, a specialist rockfall modelling programme from the University of Milan in Italy with data for the modelling supplied by CERA, CCC and GNS. This data is the same data used by other consultants commissioned by CERA and CCC in an attempt to better understand the issues affecting the Port Hills. Hy−Stone is a rockfall modelling software utilising numerical code to analyse rockfalls, the related hazard and the associated risk. While a number of remedial options were considered as part of the study it was immediately evident that the most appropriate solution to the hazard was the installation of rockfall barriers. While some areas were better suited to earth bunds, very few locations were treatable at source. Typical results indicated energies were in the order of 1,000 to 2,000 kJ with relatively low bounce heights (less than 3–4 m high). Treatment of this level of energy is relatively straight forward with proprietary products readily available. While the extent of the rockfall issue surrounding the Christchurch earthquakes is phenomenal, the requirements for rockfall protection are by no means exceptional on a global level.
Slope Stability 2013 | Abstracts | 101
Verification of Trajec3D for use in rockfall analysis at Newmont Boddington Gold
C.C. Graf Newmont Boddington Gold, Australia
T. Peryoga Newmont Boddington Gold, Australia
G. McCartney Newmont Boddington Gold, Australia
T. Rees Newmont Boddington Gold, Australia
AbstractThe Boddington gold mine is owned by Newmont Asia Pacific and is located approximately
130 km southeast of Perth in Western Australia. Operations officially commenced in 2010 with production from two large pits. At full capacity Boddington will become the largest gold mine in Australia. Boddington is located within the Saddleback Greenstone Belt and the pits are being developed in a largely hard rock environment.
In open pit mining generally, isolated falls of individual or small clusters of rock pose a risk to personnel and equipment. The aspects of interest in modelling the rockfall behaviour includes the rock trajectory path, landing distance from the bench and the lateral spread from the point of origin that have detached from the slope. Readily available software for the modelling of rockfalls simplifies the problem to two-dimensions that does not account for the three-dimensional pit surfaces, and does not represent the rock geometry. This makes rockfalls difficult to model accurately and does not address all the aspects that are of interest in the modelling of rockfall behaviour. These shortcomings were addressed in a three-dimensional rigid body rockfall analysis program software program Trajec3D (BasRock, 2013). Trajec3D is able to simulate the trajectory of rocks during free fall, rolling, bouncing and sliding.
A project was undertaken at Boddington to verify the use of Trajec3D to model rockfall events, and understand rockfall behaviour. The project involved completing a series of tests to determine the coefficient of restitution on different floor surfaces within the pit, and undertaking rockfall experiments in the pit. The experimental rockfalls were then back-analysed with Trajec3D to determine appropriate physics interaction properties.
It was found that there were some limitations to the model, however the model did aid in understanding rockfall behaviour, and potential rockfall motion paths. It is believed that the Trajec3D model provides a fair representation of the rockfalls, and is able to be used to establish a procedure whereby potential rockfall areas can be identified, and effective rockfall mitigation techniques determined.
Wall control
Slope Stability 2013 | Abstracts | 103
West Gully Upper – innovative rockfall and debris flow protection systems
H.P. Anderson Geovert Ltd, New Zealand
A. Teen Geovert Global PTE, Singapore
H. Salzmann Free Fall Geotechnical Engineering ZT GmbH, Austria
AbstractWithin PT Freeport Indonesia’s (PTFI) mining operation in Papua, Indonesia the Mill
Area complex is subject to rockfall and debris flow events which initiate from a source area approximately 1,000 m up in a steep gully known as the ‘West Gully’. Active barrier protection systems, RXI-500 (5,000 kJ) barrier, were installed to reduce likelihood of these geohazards impacting the Mill Area. However, during August 2011 an estimated 45,000 m³ failure event occurred from the West Gully Upper source area due to differential erosion and the sites tectonic setting. The mass and velocity of this failure easily exceeded the capacity of the two RX-500 barriers located in the lower section of the gully. The failure event caused significant damage and economic interruption to the Mill Area complex and blocked the critical transport corridor (Ridwan Napitupulu Road).
Following a site visit Geovert provided an options report and formally recommended increasing the overall capacity of the rockfall/debris flow protection system for the West Gully by significantly increasing individual barrier capacity from 5,000 to 8,000 kJ. PTFI as a true industry innovator committed to the GBE 8000A system prior to public knowledge of its existence and prior to the system achieving certification at the Swiss Governmental testing facility in Walenstadt. Certification was later achieved at Walenstadt in October 2011. Free Fall Geotechnical Engineering ZT GmbH modelled rockfall and debris flow anticipated trajectories and impact forces for the West Gully protection system. This modelling supported recommendations to increase the protection system capacity utilising GBE-8000A barrier technology. Rockfall 7.1 beta, by Dr. Spang Ltd, modelling confirmed 3 locations for GBE-8000A barriers to suitability retain rockfall and debris flow events in the West Gully. The proposal included provision for installation of temporary protection works to protect against geohazards while constructing barrier’s in the West Gully and contingency planning to allow for safe repair works of barrier systems if a major failure event occurs. Climatic, environmental and physical conditions were critical in pre-construction planning and during construction execution to compensate for; frequent heavy bursts of precipitation (estimated at 11 m/yr at the Mill Area complex), consideration of the project site situated at approximately 3,600 masl and no road access to the site resulting in complete reliance on tailored Helicopter transportation of all personnel, equipment and materials to site.
Slope Stability 2013 | Abstracts | 104
Rockfall stabilisation of a steep and high slope at West Angelas Mine using pre-tensioned anchored mesh
P.J.G. Lopes Geovert Pty Ltd, Australia
T.T. Le Geovert Pty Ltd, Australia
AbstractThis paper presents a rockfall protection technique employed at the West Angelas iron ore
mine located in the Pilbara region of Western Australia. The technique involves the installation of rock bolts and fully dimensioned high tensile wire mesh covering an area of approximately 6,000 m2 of the overhang 150 m above the pit floor. In order to evaluate the surface stability of the slope and to propose adequate design, an analysis was undertaken using surficial slope stabilisation calculation techniques to define nail geometry, type and diameter and appropriate mesh cover. The final design approach and construction methodology in which rope access technique drilling is required are also discussed and presented in this paper. The design of the rockfall mesh system has been proved to be satisfied as it has successfully stopped an approximately 1.5 m3 detached boulder falling off the crest in February 2012. Due to the simple installation procedure, the high tensile mesh system had allowed the project to be completed in shorter duration with minimal disruptions from technical related issues. Under Geovert’s assessment, the high tensile mesh system had saved approximately $700 k of cost against other stabilisation options such as rockfall barriers.
Slope Stability 2013 | Abstracts | 105
Rock and soil slope protection using a high stiffness geocomposite mesh system
D. Cheer Maccaferri S.p.a., Italy
G. Giacchetti Alpigeo, Italy
AbstractOne of the most common solutions adopted for the protection of vulnerable soil and rock
slopes is wire mesh, retained by a system of anchors and ropes. Different types of meshes are available from a number of manufacturers around the world. Hexagonal ‘Double Twist’ type meshes have been used very successfully in civil and geotechnical engineering projects for over 60 years but in the last 10 years many alternative meshes have been brought into the market place. This can sometimes leave designers and contractors struggling to choose the most suitable mesh for their project or having to install two different meshes together in order to take advantage of specific desirable benefits, unique to each.
Recently a revolutionary geocomposite mesh Steelgrid HR, has been developed, which is able to offer a range of advantageous mechanical and practical benefits combined with the convenience of a single mesh. Steelgrid HR is supplied as a complete ‘mesh kit’ or ‘system’ with tried and tested installation fittings to enable the contractor, designer and client to benefit from the unique capabilities of the mesh while overcoming any conceptual ambiguity regarding system implementation. The system is available with two different corrosion protection specifications to suit a variety of different project sites from near marine environments to high alpine continental areas.
Steelgrid HR has been subjected to rigorous testing conducted by a number of highly respected independent test institutions; including testing to the new UNI 11347 standard: Tests on Meshes for Slope Coverage. This testing has allowed the Steelgrid HR system to gain both the European Technical Approval (ETA) and the CE mark. The test data has been incorporated into the unique and recently revised MacRO software package that enables engineering professionals to calculate the performance of Steelgrid HR under a variety of slope stability conditions.
This paper will review existing meshes and full scale testing performed to date, provide design and installation guidance, examine the tests performed on Steelgrid HR mesh and mesh kit components and will also look into the details of the revised limit states approach version of the MacRO software package.
Slope Stability 2013 | Abstracts | 106
Landslide risk management in Australia 2013 – status of resources available to practitioners
A. Leventhal GHD Geotechnics, Australia
A. Miner AS Miner Geotechnical, Australia
B. Walker JK Geotechnics, Australia
AbstractThrough its national committee, the Australian Geomechanics Society (AGS) has long
recognised the contribution of Landslide Risk Management (LRM) to the wellbeing of the Australian community. As part of a commitment since 1985, the Society recently undertook two initiatives: the 2011 LRM ‘Risky Roadshow’ seminar series conducted throughout the nation; and in 2012 the development of an interactive ‘Education Empowerment’ website specifically directed towards LRM.
The principle objective of these initiatives was to communicate and educate, and thereby empower, landslide practitioners and regulators with knowledge and tools required to implement best practice LRM, as well as to provide information to the general Australian populace regarding landslide risk. These educational resources and tools are based upon the internationally recognised LRM guidelines and commentaries published by AGS in 2000 and 2007. It was appropriate to build upon the guideline outcomes through these recent initiatives to benefit the Australian community.
This paper provides background to the current status of LRM throughout the nation and provides advice on the package of resources available to assist practitioners in conducting landslide risk assessments.
Slope Stability 2013 | Abstracts | 107
Design and construction of an anchored soil nail wall close to movement sensitive structures
A.K. Kho Cardno Pty Ltd, Australia
M. McAuley GHD Pty Ltd, Australia
AbstractLegacy Way is a 4.6 km twin 12.4 m diameter road tunnel with approximately 3 km of surface
connections to facilitate entering and exiting the tunnels. The new roadway bypasses Brisbane CBD to the west and will connect the Western Freeway at Toowong with the Inner City Bypass (ICB) at Kelvin Grove.
As part of the Eastern surface connection works, a 12 m high × 55 m long soil nail and anchored wall retaining a soil and weathered rock slope was constructed as abutment support to the extended Inner Northern Busway (INB) bridge and Brisbane Grammar School (BGS) pedestrian bridge. The new abutment wall was an integral element of an overall solution that required addition of spans to the existing bridges and removal of the original Reinforced Soil Structure (RSS) abutments.
The near vertical new abutment wall is located approximately 1 m in front of large diameter bored piles which support the extended bridge. Resistance of lateral pile loads and restriction of movement of the new bridge abutment were key constraints in the design.
Bridge extension and construction of the new abutment wall has created sufficient space for a large buried drainage structure to carry floodwater outflow from nearby playing fields to an open channel further east. The buried drainage structure runs parallel to the ICB and supports a shared (pedestrian/bikeway) user path.
This paper provides a commentary on the design approach adopted and construction issues encountered. Validation of the design through construction support and monitoring records is also summarised.
Excavation control
Slope Stability 2013 | Abstracts | 109
Blast induced damage mechanism on final walls and the blasting methods to minimise damage
W.W. de Graaf Mining Engineering Department, University of Pretoria, South Africa
S.J. Etchells AEL Mining Services, South Africa
AbstractAt most open pit mines, profitability is affected appreciably by the final slope angles of the
pit. Steep stable and safe pit walls can be formed by accurate final wall drilling and blasting techniques. The violence of the blasting process both leaves damaged surfaces that must be made safe, and breaking beyond the desired limit will increase mining costs. Much can be done to significantly reduce the damage, although the geological conditions and geometry of excavation ultimately limits success.
The aim is to make the transition from well fragmented rock to an undamaged slope or wall in as short a distance possible. The success of final wall blasting techniques depends on the aims being achieved despite the conflict of purpose that may exist in the mine’s production environment. Various drilling and blasting techniques are applied to minimise the impact from blasting that causes damage on the perimeter wall. These techniques have a common objective to minimise fracturing and loosening of the rock beyond the excavation line, and include line drilling, pre-splitting, buffer blasting and trim blasting.
In final wall blasting, the degree of confinement of the explosives energy adjacent to the slope plays a key role in the amount of wall damage produced. The energy of the explosives should be directed away from the final wall. Avoid the false notion that the explosives energy must always be minimised to limit blast damage to the walls. The challenge remains to apply explosives energy in ways that limit damage to the walls, but produce the required fragmentation of the ore to enable high productivity. Perimeter blasting is about techniques to limit damage to the walls, by creating split surfaces to define boundaries and terminate crack development, reducing energy against the back wall, and diverting it away from the perimeter zone.
Slope Stability 2013 | Abstracts | 110
Measurements of dynamic surface strains induced by blasting near a highwall of a coal mine – a preliminary assessment
K.N. Henley Orica Australia Pty Ltd, Australia
A.T. Spathis Orica Australia Pty Ltd, Australia
AbstractFive production blasts at a coal mine were monitored at the top of the highwall using multiple
vibration monitors from which the two dimensional transient surface strains were inferred using a novel analysis method. The rock type at the top of the highwall was semi-consolidated sediments typical of natural surface cover in central Queensland coal mines. The monitors were located between 81 and 280 metres from the production blasts, and approximately 10 m from the highwall crest. Vibration levels recorded were between 50 and 226 mm/s, while maximum tensile principal strains were between 123 and 542 microstrain. No obvious surface cracks were noted at the monitoring location.
Slope Stability 2013 | Abstracts | 111
Blasting vibration assessment of rock slopes and a case study
K.W.K. Kong MWH Australia Pty Ltd, Australia
AbstractThe most common types of blasting damage are caused by ground vibration. The sudden
acceleration of the rock by the detonation energy acting on the drill hole generates an intense stress wave of both transverse and longitudinal wave motions in the surrounding rock. Key issues associated with the process of excavation and tunnelling include blast and, to a lesser extent, other construction vibration that affects the integrity of the surface structure and potentially slope stability.
The stability of slopes subject to blasting induced ground vibration may be assessed by different approaches including the pseudo-static approach, the dynamic analysis, the empirical approach and the energy approach. For soil slope stability analysis, the Pseudo-static Approach and Dynamic Analysis are generally used. However, for rock slope stability assessment under blasting vibration effects, an energy approach is normally used.
The energy approach, combined with the empirical correlation of shear strength and stiffness of rock joints developed by Barton (1990), with various joint characteristics, has been used in the analysis described in this paper. Peak particle velocity (PPV) of the potential rock block failure is a key parameter to determine the allowable charge weight per delay of the blast. Detailed discussion of the energy approach is presented in this paper and a case study illustrates the use of the method.
The allowable charge weights per delay for rock blasting which may impact on the stability of slopes can be estimated using the simple energy approach. This approach can give controllable safety limits for the works. Thus, blasting works can be carried out safely with minimum to no damage or excessive ground movements to the slopes and other sensitive receivers, if the allowable PPV and charge weights are followed, and the specified monitoring works are carried out.
Slope Stability 2013 | Abstracts | 112
Drape mesh protection at the Savage River Mine, Tasmania
B.J. Hutchison Grange Resources (Tasmania) Pty Ltd, Australia
G.K. Macqueen Grange Resources (Tasmania) Pty Ltd, Australia
S.L. Dolting Grange Resources (Tasmania) Pty Ltd, Australia
A.T. Morrison Geobrugg Australia Pty Ltd, Australia
AbstractIn June and August of 2010 Grange Resources experienced two large wall failures at their Savage
River Mine in Tasmania, Australia. These rockslides buried a significant portion of the magnetite ore scheduled to be mined in the following two years. To ensure long term ore supply, a major cutback was required to get back down onto the orebody. Several different approaches and mine plans were considered before deciding on a cast blast and drape mesh option to speed up the bench advance. Various mesh design schemes were assessed, before selecting a Geobrugg drape mesh system to cover the 60 to 80 m high, steeply dipping, haematite coated shear. The intent was to allow rapid mining bench advances during the cutback and rockslide removal process. By adopting this approach considerable time was saved by eliminating extensive pre-splitting, trim blast and rock support requirements associated with Grange’s normal mining procedures.
Two large cast blasts were taken to remove rock material in front of the back scarp. The cast blasts were each 40 m in height and cast 30–35% of the blasted rock off the face from in front of the haematite coated shear, which formed the back scarps of the two rock failures.
The drape mesh system was installed between April and October of 2011. The system was very successful in protecting personnel and equipment from rockfalls on the backscarp during the subsequent mining phase.
This paper describes the various processes associated with mine planning, cast blasting, drape mesh design, drape mesh tendering and selection, and installation; as well as the costs. The performance of the mesh in retaining potential and actual rockfalls is also described; along with issues associated with radar monitoring.
Slope Stability 2013 | Abstracts | 113
Understanding the blast damage mechanisms in slopes using observations and numerical modelling
S.J. Etchells AEL Mining Services, South Africa
E.J. Sellers JK Tech Pty Ltd, Australia
J. Furtney Itasca Consulting Group Inc., USA
AbstractObservations made in the field, together with numerical modelling using the Hybrid Stress
Blast Model (HSBM) are presented to further understand the mechanisms contributing to blast damage in pit slopes. The aim being to examine the contributing variables such as the variability of the rock mass, blast design, charging technique and current wall control techniques in the industry. The HSBM blast modelling research tool, with some improvements to the near field logic, successfully demonstrates different techniques of wall control that are being used in the industry. It is shown how the orientation of the discontinuities relative to the pit walls can negatively affect the performance of both a presplit and a post -split if not taken into consideration in the blast design. Damage reduction in a presplit requires the correct spacing, decoupling ratio and split factor. Controlling the fractures at the end of a presplit becomes important if there is a need to reduce the number of holes per delay to control vibrations and air blast, because there is an accumulation of damage into the highwall at the end of each section.
The use of post-splitting is more favourable in terms of reducing production time. Dynamic post-splits at a hard rock quarry are studied and show fair results for jointing at an acute angle to the face. Poor ground conditions result when the jointing is at an obtuse angle relative to the face. This technique should only be used if the risk on the operation is appropriately managed, and the mine is sufficiently shallow.
An effective wall control technique relies on an effective trim blast. Observations highlight damage up to ten metres or more into the slope with poor blasting, if an ineffective wall control technique were to be applied. The numerical modelling confirms that the linear charge factor is the main contributing factor to damage, although it is closely related to the powder factor and cannot be considered in isolation. Limitation of confinement is the major link to limiting damage. By understanding blast damage mechanisms, pit slope stability risks can be better quantified and modelled. This will allow optimisation of a wall control technique to a specific rock mass, and to link the expected damage on a bench scale to the overall pit slope.
