Douglas Partners Pty Ltd ABN 75 053 980 117 www.douglaspartners.com.au 1/1 Luso Drive Unanderra NSW 2526 PO Box 486 Unanderra NSW 2526 Phone (02) 4271 1836 Fax (02) 4271 1897 Brisbane • Cairns • Canberra • Central Coast • Coffs Harbour • Darwin • Geelong • Gold Coast • Macarthur Melbourne • Newcastle • Perth • Port Macquarie • Sunshine Coast • Sydney • Townsville • Wollongong Memorandum To Edenvell Pty Ltd Mr Richard Clifford [email protected]cc K F Williams & Associates Mr Andrew Purnell [email protected]From Arthur Castrissios Date 27 July 2016 Subject Proposed Residential Subdivision Stage 13 Redgum Ridge Estate, Figtree Project No. 89157.08 As requested, we have carried out a review of existing geotechnical information to provide comment on likely lot classifications and other geotechnical aspects relevant to design and construction of residential dwellings within proposed Lots 1301 – 1327 of the Redgum Ridge Estate at Figtree. The following preliminary comments are provided: A preliminary investigation was undertaken by Douglas Partners Pty Ltd (DP) prior to conceptual planning and design of the estate, with the results given in a report (Project 25662) dated 10 December 2003. The 2003 DP investigation comprised field mapping by a senior engineering geologist and the excavation of test pits followed by laboratory testing, analysis and reporting. In summary, the Stage 13 development is located within a zone nominated as being "suitable for residential development". A test pit excavated for the DP 2003 investigation (Pit 1) encountered silty topsoil to 0.2 m depth overlying residual clayey silt with weathered sandstone intersected at 0.5 m depth. The rock was initially extremely low strength becoming medium to high strength at near refusal of the backhoe bucket at a depth of 1.0 m. The test pit log from the DP 2003 report is attached for information. A geotechnical investigation of adjacent Stage 4 was undertaken by DP at the completion of earthworks, with the results given in a report (Project 25662.19) dated 17 March 2011. The investigation comprised the excavation of test pits, followed by laboratory testing of selected samples, engineering analysis and reporting. The test pits relevant to Stage 13 (namely Pits 102 and 105) encountered topsoil to 0.3 m depth overlying stiff to very stiff residual clays. Weathered sandstone and latite were intersected at depths of 0.9 m and 0.8 m respectively and continued to the termination depths of 1.5 m and 1.4 m. The test pit logs from the Stage 4 investigation relevant to Stage 13 are also attached. No free groundwater was observed in the previous pits for the short time that they were left open. It is noted that groundwater levels are dependent on preceding climatic conditions and soil permeability, and can therefore fluctuate with time. Notwithstanding the above, it is noted that due to the topographical location, significant variability in subsurface conditions can be expected.
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Douglas Partners Pty Ltd
ABN 75 053 980 117
www.douglaspartners.com.au
1/1 Luso Drive
Unanderra NSW 2526
PO Box 486
Unanderra NSW 2526
Phone (02) 4271 1836
Fax (02) 4271 1897
Brisbane • Cairns • Canberra • Central Coast • Coffs Harbour • Darwin • Geelong • Gold Coast • Macarthur Melbourne • Newcastle • Perth • Port Macquarie • Sunshine Coast • Sydney • Townsville • Wollongong
Based on the work undertaken to date, anticipated subsurface conditions and experience on the
adjacent stages of the Redgum Ridge estate, it is expected that Lots 1301 – 1327 would be
classified as either Class M (moderately reactive) or Class H1 (highly reactive) in accordance with
AS2870 – 2011 Residential Slabs and Footings. It is also noted that some lots will include
controlled filling that will be placed during subdivision construction, the extent and depth of which
will be discussed in the lot classification report.
A formalised lot classification report will be prepared at the completion of subdivision
construction. The following comments are provided as a preliminary guide to geotechnical
requirements for future development.
Residential construction on the lots should be relatively straightforward with footing system
selection to be in accordance with AS 2870 – 2011. Notwithstanding this, due to the relatively
shallow depth to rock and the likelihood of variable founding conditions following site preparation
for building platforms, it is suggested that footings be founded on weathered rock. The main
advantage of a footings-to-rock system is that settlements would be minimal and possibly result in
minimal site preparation.
Where footing systems are proposed adjacent to services or located through areas of
uncontrolled fill (for example, following construction of a level building platform without
engineering control), local deepening of the footing trenches or alternatively the inclusion of piers
will be required with founding levels to be constructed below the zone of influence of service
trenches and to the weathered rock in the areas of fill. Where footings are likely to intersect fill
and residual soils, reference should be made to AS 2870 regarding provision of articulation within
the structure and construction of a foundation system that provides uniform bearing in the
weathered rock.
All footing systems should be designed and constructed in accordance with engineering
principles, with care exercised to ensure that footing trenches and/or piers are inspected for
design compliance. As a guide, footing design could be based on an allowable end bearing
pressure of 500 kPa in the weathered rock, with a minimum socket length of 300 mm (or prior
refusal) suggested.
Excavation and filling should generally be limited to a maximum vertical height of 1.5 m
respectively below or above the existing ground surface. Placement of all filling should be under
controlled conditions. Permanent batters within any such excavation or controlled filling should
be no greater than 3(H):1(V) and should be topsoiled and vegetated as soon as possible after
construction to minimise soil erosion. Proposed earthworks that exceed the above requirements
should be subject to review by a geotechnical engineer during the design phase of the individual
project. Excavations that exceed 1.5 m must be supported by engineer-designed retaining walls
founded on bedrock. However, it must be accepted that creep movement in retaining walls
constructed perpendicular to the slope is probably unavoidable, due to the high active pressures
of the retained material.
The developed lots should be maintained in accordance with the CSIRO publication "Foundation
Maintenance and Footing Performance: A Homeowners Guide". Whilst it must be accepted that
minor cracking in most structures is inevitable, the guide describes suggested site maintenance
practices aimed at minimising foundation movement or floor slab movement to keep cracking
within acceptable limits.
July 2010
Introduction These notes have been provided to amplify DP's report in regard to classification methods, field procedures and the comments section. Not all are necessarily relevant to all reports. DP's reports are based on information gained from limited subsurface excavations and sampling, supplemented by knowledge of local geology and experience. For this reason, they must be regarded as interpretive rather than factual documents, limited to some extent by the scope of information on which they rely. Copyright This report is the property of Douglas Partners Pty Ltd. The report may only be used for the purpose for which it was commissioned and in accordance with the Conditions of Engagement for the commission supplied at the time of proposal. Unauthorised use of this report in any form whatsoever is prohibited. Borehole and Test Pit Logs The borehole and test pit logs presented in this report are an engineering and/or geological interpretation of the subsurface conditions, and their reliability will depend to some extent on frequency of sampling and the method of drilling or excavation. Ideally, continuous undisturbed sampling or core drilling will provide the most reliable assessment, but this is not always practicable or possible to justify on economic grounds. In any case the boreholes and test pits represent only a very small sample of the total subsurface profile. Interpretation of the information and its application to design and construction should therefore take into account the spacing of boreholes or pits, the frequency of sampling, and the possibility of other than 'straight line' variations between the test locations. Groundwater Where groundwater levels are measured in boreholes there are several potential problems, namely: • In low permeability soils groundwater may
enter the hole very slowly or perhaps not at all during the time the hole is left open;
• A localised, perched water table may lead to an erroneous indication of the true water table;
• Water table levels will vary from time to time with seasons or recent weather changes. They may not be the same at the time of construction as are indicated in the report; and
• The use of water or mud as a drilling fluid will mask any groundwater inflow. Water has to be blown out of the hole and drilling mud must first be washed out of the hole if water measurements are to be made.
More reliable measurements can be made by installing standpipes which are read at intervals over several days, or perhaps weeks for low permeability soils. Piezometers, sealed in a particular stratum, may be advisable in low permeability soils or where there may be interference from a perched water table. Reports The report has been prepared by qualified personnel, is based on the information obtained from field and laboratory testing, and has been undertaken to current engineering standards of interpretation and analysis. Where the report has been prepared for a specific design proposal, the information and interpretation may not be relevant if the design proposal is changed. If this happens, DP will be pleased to review the report and the sufficiency of the investigation work. Every care is taken with the report as it relates to interpretation of subsurface conditions, discussion of geotechnical and environmental aspects, and recommendations or suggestions for design and construction. However, DP cannot always anticipate or assume responsibility for: • Unexpected variations in ground conditions.
The potential for this will depend partly on borehole or pit spacing and sampling frequency;
• Changes in policy or interpretations of policy by statutory authorities; or
• The actions of contractors responding to commercial pressures.
If these occur, DP will be pleased to assist with investigations or advice to resolve the matter.
July 2010
Site Anomalies In the event that conditions encountered on site during construction appear to vary from those which were expected from the information contained in the report, DP requests that it be immediately notified. Most problems are much more readily resolved when conditions are exposed rather than at some later stage, well after the event. Information for Contractual Purposes Where information obtained from this report is provided for tendering purposes, it is recommended that all information, including the written report and discussion, be made available. In circumstances where the discussion or comments section is not relevant to the contractual situation, it may be appropriate to prepare a specially edited document. DP would be pleased to assist in this regard and/or to make additional report copies available for contract purposes at a nominal charge. Site Inspection The company will always be pleased to provide engineering inspection services for geotechnical and environmental aspects of work to which this report is related. This could range from a site visit to confirm that conditions exposed are as expected, to full time engineering presence on site.
pp = 220-240kPa
0.25
0.85
1.6
U
D
D
TOPSOIL - brown clay with somesilt, fine to medium gravel(sandstone), roots and rootlets,humid to dampCLAY - very stiff, orange brown andgrey clay with some cobbles(sandstone) and sand, humid todamp (RESIDUAL)
TUFFACEOUS SANDSTONE - lowto medium strength, moderatelyweathered, orange brown tuffaceoussandstone
SAMPLING & IN SITU TESTING LEGENDA Auger sample G Gas sample PID Photo ionisation detector (ppm)B Bulk sample P Piston sample PL(A) Point load axial test Is(50) (MPa)BLK Block sample Ux Tube sample (x mm dia.) PL(D) Point load diametral test Is(50) (MPa)C Core drilling W Water sample pp Pocket penetrometer (kPa)D Disturbed sample Water seep S Standard penetration testE Environmental sample Water level V Shear vane (kPa)
BORE No: 102PROJECT No: 25662.19DATE: 29/3/2010SHEET 1 OF 1
WATER OBSERVATIONS: No free groundwater observedTYPE OF BORING:RIG: Cat 325B - 600mm bucket DRILLER:
REMARKS:SURVEY DATUM:
CASING:LOGGED: RJH
0.25
0.75
1.4
D
D
TOPSOIL - grey brown friableslightly gravelly (fine to mediumlatite) silty clay with some roots androotlets, humidGRAVEL AND SILTY CLAY -typically stiff, light brown grey cobblymedium to coarse gravel (latite) andsilty clay, humid to damp
LATITE - medium to high strength,moderately weathered, orange greylatite recovered as gravel and cobblesized blocks
- becoming cobble and bouldersized blocks below 1.3m
SAMPLING & IN SITU TESTING LEGENDA Auger sample G Gas sample PID Photo ionisation detector (ppm)B Bulk sample P Piston sample PL(A) Point load axial test Is(50) (MPa)BLK Block sample Ux Tube sample (x mm dia.) PL(D) Point load diametral test Is(50) (MPa)C Core drilling W Water sample pp Pocket penetrometer (kPa)D Disturbed sample Water seep S Standard penetration testE Environmental sample Water level V Shear vane (kPa)
