Geotek-rock Engineering for Underground

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ROCK ENGINEERING IN

UNDERGROUND MINING

Laboratorium Geomekanik dan Rekayasa Batuan

Program Studi Teknik Pertambangan

Universitas Hasanuddin


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INTRODUCTION

‘Rock mechanics’ is the study of mechanics applied to rock and rock masses

'Engineering rock mechanics' is this study within an engineering context,rather than in the context of natural processes that occur in the Earth's crust,such as folding and faulting.

‘Rock engineering’ refers to the process of engineering with rock, andespecially to creating structures on or in rock masses, such as slopesalongside roads and railways, dam foundations, shafts, tunnels, caverns,mines, and petroleum wellbores.Geotechnical engineering , has been defined as “the application of thesciences of soil mechanics and rock mechanics, engineering geology andother related disciplines to civil engineering construction, the extractiveindustries and the preservation and enhancement of the environment


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Teknik sipil Pertambanga

- Lokasi dekat permukaan- Permanen- Keamanan dan kenyamanan tinggi- Soil - batuan

- Lokasi dangkal – dalam- Relatif Sementara- Keamanan- Batuan


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Management

Mine geology Rock mechanics

PrMineplanning and

design


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ROCK PROPERTIES AND MECHANICAL BEHAVIOR

Rock density ( r ) is a measure of mass of the rock contained in a given

unit volume (density = mass/volume).Porosity ( f ) is defined to be the ratio of a volume of void spaces withina rock to the total bulk volume of the rock.

Rock physical properties

• Berat contoh asli (natural): Wn• Berat contoh kering (sesudah dimasukkan ke dalam oven

selama 24 jam dgn T ± 90 o C): Wo• Berat contoh jenuh (sesudah dijenuhkan dlm air selama

24 jam): Ww• Berat contoh jenuh didalam air: Ws• Volume contoh tanpa pori-pori: Wo - Ws•

Volume contoh total: Ww - Ws


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Rock mechanical properties mainly include elastic modulus (

Poisson’s ratio ( n), and rock strength (compressive strength, tensilestrength, shear strength).

Rock mechanical properties


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UCS classification


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ROCK MASS CLASSIFICATION

Rock material is the term used to describe the intact rock betweendiscontinuities; it might be represented by a hand specimen or pieceof drill core examined in the laboratory


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The rock mass is the total in situ medium containing bedding planesfaults, joints, folds and other structural features.

Rock masses are discontinuous and often have heterogeneous and

anisotropic engineering properties.


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ROCK QUALITY DESIGNATION INDEX (RQD) , DE1967

Palmstrom, 1982

RQD = 115 – 3.3 J v

J v is number of joints presentin a cubic metre of rock


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ROCK MASS RATING (BIENIAWSKI, 1973)


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Rock Mass Rating System (After Bieniawski, 1989).


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A tunnel is to be driven through a slightly weathered granite with adominant joint set dipping at 60 o against the direction of the

Index testing and logging of diamond drilled core give typical Point-load strength index values of 8 MPa and average RQD valuThe slightly rough and slightly weathered joints with a separationmm, are spaced at 300 mm . Tunnelling conditions are anticipated be wet .

Condition of discontinu:1-3 m discontinuity length, separation 0.1-1.0 mm, slightly rough, no infilling, and (slightlyweathered

Quis-1


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A tunnel is to be driven through a slightly weathered granite with a dominant joint set dippingat 60 o against the direction of the drive. Index testing and logging of diamond drilled coregive typical Point-load strength index values of 8 MPa and average RQD valuesslightly rough and slightly weathered joints with a separation of < 1 mm, are spaced atmm . Tunnelling conditions are anticipated to be wet .

Condition of discontinu:1-3 m discontinuity length = 4,separation 0.1-1.0 mm = 4,slightly rough = 3,no infilling = 6,slightly weathered = 5


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Relationship between Stand-up time, span

and RMR classification, after Bieniawski (1989).


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NGI TUNNELLING QUALITY INDEXROCK MASS QUALITY - Q SYSTEM (BARTON, LIEN and1974)

Q =

Q is rock mass quality Q-system is rock quality designation

is joint set number is joint roughness number is joint alteration is joint water

is stress reduction factor

Norwegian Geotechnical Institute (NGI).


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A. Block Sizes1. Rock Quality Designation (RQD)2. Number of joint sets ( )

B. Inter-block Shear Strength3. Roughness of the most unfavourable joint or discontinuity ( )4. Degree of alteration or filling along the weakest joint ( )

C. Active Stresses5. Water inflow ( )6. Stress condition ( )

Cla


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Claindiused(Ba


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QUIS-2

A highly fractured siltstone rock mass, found to have 2 joint sets andmany random fractures, average RQD is 41%, joints appearscontinuous observed in tunnel, joint surfaces are slickensided andundulating, and are highly weathered, joint are separated by about 3-5 mm, filled with clay, average rock material uniaxial compressivestrength is 65 MPa, inflow per 10 m tunnel length is observed atapproximately 50 litre/minute, with considerable outwash of jointfillings. The tunnel is at 220 m below ground. Unit weight of the sillstoneis 0.027MN/m 3.


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SUPPORT

Barton et al. (1974) defined a parameter that they called EDimension, De , of the excavation. This dimension is obtained bydividing the span, diameter or wall height of the excavation by aquantity called the Excavation Support Ratio, ESR.

= , ℎ ℎ ( ) ,

Table Excavation support categories and their ESR values (After Barton et


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Table Excavation support categories and their ESR values (After Barton etal., 1974).


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The Q support chart (from Grimstad and Barton, 1993).


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CORRELATION OF ROCK MASS CLASSIFICATIONS


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Choquet and Hadjigeorgiou (1993).


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GEOLOGICAL STRENGTH INDEX (HOEK, 1994)

It was aimed to estimate the reduction in rock mass strength fordifferent geological conditions

The system gives a GSI value estimated from rock mass structure androck discontinuity surface condition.

The direct application of GSI value is to estimate the parameters in theHoek-Brown strength criterion for rock masses.


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GENERALISED HOEK-BROWN CRITERION

= 3 + (3 + )

3 are the maximum and minimum stresses is the value of the Hoek-Brown constant m for the rock mass

s and a are constants which depend upon the rock mass characteristics is the uniaxial compressive strength of the intact rock pieces

For the intact rock pieces

= 3 + (3 + 1) .5


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In order to use the Hoek-Brown criterion for estimating the strength and

deformability of jointed rock masses, three ‘properties’ of the rock mass have to beestimated. These are;

1. the uniaxial compressive strength s ci of the intact rock elements,2. the value of the Hoek-Brown constant mi for these intact rock elements, and3. the value of the Geological Strength Index GSI for the rock mass.


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Field estimates of uniaxialcompressive strength.


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Values of the constant mi for intact rock,by rock group. Note that valuesin parenthesis are estimates


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Idealised diagram showing thetransition from intact to a heavily

jointed rock mass with increasingsample size

Once the Geological Strength Index has been estimated the parameters that describe the rock


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Once the Geological Strength Index has been estimated, the parameters that describe the rockmass strength characteristics, are calculated as follows:

= exp ( − 10028

)


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• For better quality rock masses (GSI > 25), the value of GSI can be estimated directly from1976 version of Bieniawski’s Rock Mass Rating, with the Groundwater rating set to 10 (dry) athe Adjustment for Joint Orientation set to 0 (very favourable) (Bieniawski 1976).

• For very poor quality rock masses the value of RMR is very difficult to estimate and tbetween the ratings no longer gives a reliable basis for estimating rock mass strength.Consequently, Bieniawski’s RMR classification should not be used for estimating the GSI vafor poor quality rock masses (RMR < 25) and the GSI charts should be used directly.

If the 1989 version of Bieniawski’s RMR classification (Bieniawski 1989) is used, thenGSI = RMR89’ - 5

where RMR89’ has the Groundwater rating set to 15 and the Adjustment for Joint Oriento zero.


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Characterisation of a blocky rock masses onthe basis of particle interlocking anddiscontinuity condition. After Hoek, Marinosand Benissi (1998).


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Characterisation of a schistosemetamorphic rock masses on the basisof foliation and discontinuity condition.(After M. Truzman, 1999)

REFERENCES


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REFERENCES

Bieniawski, Z.T., 1974, Geomechanics classification of rock masses and its application in tunnelingProc. 3 rd Congress of International Society for Rock Mechanics, Denver, 27-32

Bieniawski, Z.T., 1989, Engineering rock mass classifications, A complete manual for engineers andgeologists in mining, civil, and petroleum engineering , Jhon Wiley & Sons, USABarton, N., Lien, R., and Lunde, J., 1974, Engineering classification of rock masses for the desigtunnel support , Rock Mechanics 6, 189-236

Deere, D.U., Hendron, A.J., Patton, F.D., Cording, E.J., 1967, Design of surface and near surconstruction in rock , Proc. 8 th U.S. Symposium Rock Mechanics, New York, 237-302

Grimstad, E., and Barton, N., 1993, Updating the Q-System for NMT , Proc. Of the InternatSymposium on Sprayed Concrete-Modern Use of Wet Mix Sprayed Concrete for UndergroundSupport, Fagernes

Hoek E. and Brown E.T., 1980: Underground excavations in rock , Institution of Mining andLondon

Evert Hoek , 2001, Rock mass properties for underground mines

Brady and Brown, 2005, Rock mechanics for underground mining, third edition , Kluwpublishers,New York, Boston, Dordrecht, London, Moscow

Peng, S., and Zhang, J., 2007, Engineering Geology for Underground Rocks , Springer


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Thank

Purwipurr0812

mailto:[email protected]:[email protected]:[email protected]:[email protected]


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