Australian Geomechanics Society Western Australia – 2010 Meetings
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9 February 2010
Lessons Learnt from Numerical Analyses of Geotechnical Problems
Mostafa Ismail and Sergei Terzaghi
This presentation will be in two parts with Dr Mostafa Ismail leading the mainpresentation with a closing presentation by Sergei Terzaghi on specific numerical modeling for tunnels including a brief commentary on soil-structure interaction effects.
Complexity of soil structure interaction problems is increasing due to continuing demandon existing infrastructures, including tunneling, underpinning activities, vibration control, as well as extension of existing facilities. This complexity is normally exacerbated bypotentially very complex geotechnical conditions and possible requirements for groundimprovements to otherwise inferior ground conditions. Handling such complexities requireshigh level of numerical expertise, clear understanding of soil behavior, awareness oflimitations of existing numerical tools and willingness to mitigate inherent risk byundertaking efficient site investigation and lab testing campaigns. This presentationcovers a few lessons learnt from projects involving numerical analysis from Australia andoverseas with focus on tunneling. The lessons highlight some of the critical issues toconsider when modeling soil-structure interaction problems. Focus is made on modelingand calibration of parameters of soft clay, selection of constitutive models, determination ofmodel parameters and associated sensitivity analyses, and details required to modelstructural elements. Emphasis and reference will be made to laboratory testing and howthis can be used to determine and calibrate soil parameters.
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22 February 2010
The Magic of Sands
Prof David Muir Wood
Note that this meeting will be held at Weatherburn Lecture Theatre, University of Western Australia.
David Muir Wood will reprise and update his Bjerrum lecture, presented recently in Oslo. The lecture begins with a description of an investigation performed at the WAC Bennett Dam, British Columbia, following the appearance of sinkholes at the dam crest. Investigations showed that there had apparently been movement of fine material out of the core of the dam. To be able to predict the mechanical consequences of such movement of material, a class of soil model that is able to accommodate changes in both density and grading of the soil is required. An outline of features of the Severn-Trent sand model - which incorporates effects of density variation - is presented and a suggestion is made for ways this model might be extended to include effects of changing particle size distribution.
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9 March 2010
Urban Stormwater and Groundwater Management for Water Sensitive Urban Design Outcomes
Bill Till MIEAust CPEng.
The water sensitive approach to stormwater management aims to maintain the pre-development hydrologic regime. The Department of Water is promoting the design of stormwater infrastructure that addresses both quantity and qualitymanagement during frequent, low intensity rainfall events. Traditional design of stormwater infrastructure focused solely on quantity management and ‘disposal’to provide flood protection during infrequent, high intensity events.
The Department of Water is addressing ‘flow rate and volume’ management up to the 1 year ARI event with the introduction of the following criterionfor assessment of urban developments: ‘for the critical 1 year average recurrence interval (ARI) event, the post development discharge volume and peak flow rates shall bemaintained relative to pre-development conditions in all parts of the catchment’.
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13 April 2010
Geotechnical Aspects of the Port Geographe development
Geoffrey Cocks
Port Geographe is a residential canal development and marina located a few kilometres east of Busselton in Western Australia. Much of the development is located over dune sand and estuarine deposits. Extensive use has been made of surcharge preloading as a foundation improvement technique to treat the organic silt thatunderlies much of the site. The paper describes the process used to design andmonitor the effectiveness of the surcharge preloading, the site classification system developed to convey to the Shire of Busselton and to Structural Engineers what thefooting requirements are, stability analysis of canal edge walls, the use of Laterite rockfor breakwaters and rip rap, the design oftemporary bunds and use of soak wells and subsoil drains.
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11 May 2010
The challanges of geohazard prediction when operating in the marine environment
Fiona Fitzpatrick
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18 May 2010
New piling code
Gary Chapman
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June 10, 2010
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June 11-12, 2010
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13 July 2010
AGS Young Geotechnical Professionals’
Evening Seminar and the 9th Dr Baden Clegg AwardThis annual event gives a platform for our younger (under 35) geo-professionals to present their work, gain feedback from experienced colleagues and become more involved in AGS activities. Please support them by coming along to what should be a varied, interesting and exciting evening. There will be four presentations, each 10 minutes long, with 5 minutes for questions after each talk. The Dr. Baden Clegg Award will be awarded to the best contribution.
John McDermott - Design, Excavation and Performance of Rock Cuttings on the Karratha to Tom Price Road, Stage 2
Construction of the Stage 2 Karratha Tom Price Road (KPT2) included excavation of about 130 cuttings along, which total about 18.5 km in length. Design and Construction was undertaken by the Millstream Link Alliance, which is a “pure alliance” that comprises Main Roads Western Australia, MacMahon Contractors Pty Ltd, Coffey International Pty Ltd and GHD Group Pty Ltd.
A total engineering geology approach was adapted to the design of cuttings, which focussed on understanding the geology rather than “drill first and think later”. Cut slopes, catch ditch widths and bench widths were based on a combination of field observations on existing rail cuttings, geological mapping, modelling of fallen rocks using the computer simulation programme “ROCFALL” and a Quantitative Risk Assessment (QRA). An ongoing design assessment was also applied where after initial excavation had begun, the batters were flattened to suit the exposed ground conditions.
Tim Nash - The Effectiveness of an Impact Roller for Foundation Treatment in Alluvial Sandy Clays
During ground-breaking geotechnical investigations for a heavy haul railway that crosses a section of the Robe River floodplain in the Pilbara region of Western Australia, the upper alluvial soils displayed unusual and concerning behaviour by what appeared to be a dramatic loss of strength when saturated. In general, the geological profile comprises up to 4.0m of sandy clay overlying variably cemented calcrete and gravels which are underlain by basement sandstone.
Preliminary laboratory testing results pointed to a classic ‘Pindan’ type soil with a relatively high void ratio, partial collapse potential and a significant order of magnitude reduction in strength when saturated. This, combined with the investigation observations and the cost of treating up to 14km of foundations, lead to a re-think of traditional deep boxout foundation treatment by assessing the effectiveness of a square dynamic impact roller.
Russel Pol - Piezocone Penetration Testing of Fallow and Operational Tailings Storage Facilities
Piezocone Penetration Tests (PCPTs) on both operational and fallow Tailings Storage Facilities (TSFs) are a useful tool to further increase our understanding of tailings behaviour both during and after deposition. PCPT investigations have been carried out on two TSFs, five years apart. One of the TSF was fallow for the five year period, while the other was operational. Where possible, the PCPTs were carried out adjacent to previous locations so that a comparison of the shear strength and pore pressure profiles could be carried out.
Comparing the results of the piezocone investigations conducted on the fallow TSF, it was identified that the majority of the tailings strength profile remained relatively consistent with depth. However, near the surface, an increase (up to 100%) in the shear strength was observed up to 5 m depth. The strength increase of the tailings near the surface is due to evaporative desiccation, leading to the over-consolidation of the tailings and a subsequent gain in strength. It was also observed that the in situ silty clay material below the tailings had increased in strength, with normal consolidation occurring due to the load applied by the tailings. A consistent hydrostatic pore pressure profile, used to estimate the phreatic surface within the TSF, was not readily identifiable within the fallow TSF for either the 2004 or 2009 investigation.
Gary Webley - A case history for the Southern Seawater Desalination Plant
WA’s Water Corporation announced in 2007 that the Southern Seawater Desalination Plant (SSDP) would be commissioned as the state’s second major source of desalinated water. On completion, the plant at Binningup (35km North of Bunbury) will produce 50 gigalitres of water per year (with the potential to expand to 100 GL). GFWA were contracted by the Southern SeaWater Alliance (SSWA) to construct the diaphragm walls that form the Intake Pump Station (IPS). Construction was carried out between September 2009 and April 2010.
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August 10 2010
Diaphragm Walls – Design and Construction
Ronan Leroy
The presentation will initially review the concept, objectives and construction method of diaphragm walls. This will be followed by an interesting case study of a quay project whose concepts can be applied to projects of similar nature in Western Australian ports. Also, the concept of curved diaphragm walls without anchors will be introduced and a recent project which has utilized three cellular diaphragm walls for one of the world’s largest private condominiums in Singapore will be reviewed in detail.
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August 24 2010
Rock Mass Characterisation
Paul Marinos
The presentation deals with the integration of site geology with engineering requirements. Methods of rock mass characterization can now be tested with the aid of numerical analyses, and the suitability of the predictions they lead to can be tested with site instrumentation.
Rock mass classification systems (such as RMR and Q) played an important role in tunnel design and also in estimating rock mass properties. With the development of extremely powerful microcomputers and of user-friendly software there was a higher demand for reliable input data related to rock mass properties required as input into numerical analysis or close form solutions for designing tunnels. This necessity led to the development of a different set of rock mass classification. The Geological Strength Index is such a classification. The geological character of rock material, together with a visual assessment of the rock mass are used as a direct input for the selection of parameters relevant for the prediction of rock mass strength and deformability.
A description of the Geological Strength index (GSI) will be presented with suggestions for its use and discussion on its limitations. One of the advantages of the index is that the geological reasoning it embodies allows adjustments of its ratings to cover a wide range of rock masses and conditions including complex rock masses with lithologic variety.
