Coffey Geotechnics Pty Ltd

Lane Cove, Australia

Coffey Geotechnics Pty Ltd

Lane Cove, Australia
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Fatahi B.,University of Technology, Sydney | Fatahi B.,Coffey Geotechnics Pty Ltd. | Khabbaz H.,University of Technology, Sydney | Indraratna B.,University of Wollongong
Ecological Engineering | Year: 2010

Bioengineering features of native vegetation are currently being evolved to enhance soil stiffness, slope stabilisation and erosion control. The effects of tree roots on soil moisture content and ground settlement are discussed in this paper. Matric suction induced by tree roots is a key factor, governing the properties of unsaturated soils, directly imparting stability to slopes and resistance for yielding behaviour. A mathematical model for the rate of root water uptake that considers ground conditions, type of vegetation and climatic parameters has been developed. This study highlights the inter-related parameters contributing to the development of a conceptual evapo-transpiration and root moisture uptake equilibrium model that is then incorporated in a comprehensive numerical finite element model. The developed model considers fully coupled-flow-deformation behaviour of soil. Field measurements obtained by the Authors from a site in Victoria, South of Australia, are used to validate the model. In this study, the active tree root distribution has been predicted by measuring soil organic content distribution. The predicted results show acceptable agreement with the field data in spite of the assumptions made for simplifying the effects of soil heterogeneity and anisotropy. The results prove that the proposed root water uptake model can reliably predict the region of the maximum matric suction away from the tree axis. © 2009 Elsevier B.V. All rights reserved.

Waddell P.,Coffey Geotechnics Pty Ltd
Proceedings of the Institution of Civil Engineers: Geotechnical Engineering | Year: 2013

Creep settlement is an important aspect to consider where development is planned over deep compacted fill. This paper presents a case study of an earthworks design for infilling a quarry pit with sandstone and shale derived material and a comparison of predicted and monitored creep settlements. Laboratory testing was carried out during filling to assess the creep characteristics of available infilling materials. Based on the laboratory testing the influence of saturation on creep rates is discussed. Settlement monitoring points across the infilled quarry were monitored for up to 455 days. Predicted creep rates based on the results of the testing are compared with predictions based on monitoring. Monitored settlements within a few years of fill placement were variable and substantially greater than predictions based on the laboratory testing. Longer term monitoring data indicates that settlements are likely to be less than predictions based on laboratory testing. The results suggest that predictions over 30 years based on laboratory testing are conservative and lie within the normal range of accuracy of geotechnical predictions.

Mather P.,Coffey Geotechnics Pty. Ltd.
Australian Geomechanics Journal | Year: 2013

The occurrence of karst limestone conditions within Western Australia is not well recognised within the general community but can be of major engineering significance for developments that are impacted by it. The presence and engineering significance of karstic limestone on the Swan Coastal Plain has been recorded by local Engineering Geologists with the first officially published recognition presented in the 1:50,000 scale Environmental and Engineering Geology Series Yanchep Sheet in 1986. The Geological Survey of Western Australia (GSWA) mapping highlighted a significant, well defined zone of karst phenomena within Tamala Limestone extending from Joondalup to Two Rocks. Increasing pressure from urban development along Perth's northern corridor lead to several "near miss" incidents which precipitated the incorporation of a requirement for all development applications within the City of Wanneroo to include consideration of the potential for karst. To date, the published literature relating to karst on the Swan Coastal Plain has been limited to geological descriptions of the phenomena. Although the potential karst hazard is now widely recognised within the geotechnical community there has been very little published information relating to geotechnical design considerations and strategies for urban development within areas affected by karstic limestone relating specifically to the Swan Coastal Plain. Considerable work has been completed over the past decade relating to the identification of karstic ground conditions and geotechnical design strategies to manage potential risks. In addition, the existence of additional areas of karstic limestone has been identified within the City of Cockburn and City of Mandurah.

Flux S.,Coffey Geotechnics Pty. Ltd.
Australian Geomechanics Journal | Year: 2013

This paper presents a comparison of inferred California Bearing Ratio (CBR) results obtained from a 4.5 kg Clegg Hammer, 20 kg Clegg Hammer, Perth Sand Penetrometer (PSP) and Dynamic Cone Penetrometer (DCP). Fieldwork was undertaken on four occasions at three locations within the Perth metropolitan area, namely at Preston Beach (Safety Bay Sand), Muchea (Colluvial Sand), and twice at Cockburn (engineered fill and Tamala Sand, the name of the sand derived from the Tamala Limestone). CBR values were inferred and the results from the different pieces of field equipment compared. Overall, at the locations tested, the 4.5 kg Clegg Hammer gave results that produced higher inferred CBR values, whilst the PSP inferred lower CBR values, with the CBR values inferred from the DCP and 20 kg Clegg Hammer in between.

Mather P.,Coffey Geotechnics Pty. Ltd.
Australian Geomechanics Journal | Year: 2013

On the 27th September 2005 a small landslide was noticed across Lewana Road, located approximately 20 km northeast of Nannup, Western Australia. When first observed the landslide was approximately 20 m long. Within a few days the landslide had removed a section of Lewana Road and increased to 150 m in length to be potentially threatening the Nannup-Balingup Road and Blackwood River located another 70 m down slope. Routine monitoring of the landslide was initiated and continued with works to improve local drainage and divert surface water away from the immediate landslide area. A geotechnical consultant was engaged to carry out a site visit as part of an assessment of the landslide occurrence and to provide advice on potential risks for the major road and Blackwood River located down slope. The potential causes of the Lewana Road landslide included a wide range of naturally occurring features including relatively steep topography, above average rainfall and shallow soil overlying rock with unfavourably orientated geological structures concentrating subsurface water flows. In conjunction with these naturally occurring features were a range of man made influences arising from recent removal of vegetation through clear felling of tree plantations, localised over steepening of slopes associated with cut to fill earthworks to construct skyline pads for tree harvesting and the concentration of surface water runoff associated with road drainage. Although the Lewana Road Landslide was a relatively minor feature and did not progress to become a significant occurrence, it provides a useful insight into the range of naturally occurring features and man made influences that are commonly associated with landslides. In addition it provides a useful example of the types of management and remediation responses that can be adopted to limit and contain potential damage to existing infrastructure and environmentally sensitive areas that may be threatened by landslides.

Bridges C.,Coffey Geotechnics Pty Ltd | Gudgin J.,Coffey Geotechnics Pty Ltd
Proceedings of the Institution of Civil Engineers: Geotechnical Engineering | Year: 2014

The Airport Link project in Brisbane, Australia, involved 15 km of tunnelling including 5.7 km of twin road tunnels, busway tunnels and connecting ramps. The Kedron area is the location of a number of entry and exit ramps which join the tunnel. The construction site consisted of a number of tunnels crossing each other and formed using a number of techniques. Access was required to a maximum of 18 m below ground level to allow for the construction of a pile-supported capping slab, which would act as a roof slab for a mined tunnel passing east to west. This paper presents details of the design and construction of the soil-nailed walls which provided support to three sides of this excavation. The excavation also provided access for commencement of a mined tunnel using canopy tubes heading eastward through one of the soil-nailed walls. The project constraints meant that the solution required close coordination between the contractor and the designers of the temporary and permanent works. The excavation was constructed successfully and has now been decommissioned. Design risks were managed throughout construction through continuous on-site observation and a comprehensive monitoring programme. © ICE Publishing: All rights reserved.

Wong P.K.,Coffey Geotechnics Pty Ltd | Oliveira D.,Coffey Geotechnics Pty Ltd
Australian Geomechanics Journal | Year: 2012

As part of the Barangaroo South project, pile load tests were carried out on two prototype rock socketed piles (SC-01 and SC-02) in Sydney Sandstone to validate the design. The pile load tests were carried out using the bi-directional O-Cell method on 750 mm diameter piles having rock socket lengths of 7.85 m (SC-01) and 6.38 m (SC-02). The target O-Cell test load was 17 MN, giving a total potential maximum test load of 34MN (i.e. shaft plus base) on each pile. Once the testing reached the required target test load, the O-Cell was loaded to its maximum capacity of about 26 MN. Assuming the O-Cell load recorded beyond the calibrated range is valid, the maximum test load reached is equivalent to a total capacity of 52MN on each pile. Prior to the O-Cell testing of the first test pile (SC-02), a Class A prediction was carried out. In this paper, actual test pile load-deformation results are compared to the Class A prediction, together with a back-analysis of the O-Cell testing using numerical methods for calibration of rock stiffness and assessment of top-load pile response. The Class A prediction of SC-02 using the method given in Fleming (1992) and adopted foundation design parameters gave good match with the actual test results. SC-02 was back-analysed using numerical methods (program FLAC3D) to assess the equivalent secant modulus of the rock. Analyses of the top load pile response were then carried out using FLAC3D and program PIES (the software used for the foundation design of the project). By comparing the top-load analysis results with those inferred from the O-Cell test, the ultimate resistance parameters were confirmed but it was assessed that the design stiffness parameters adopted may be optimistic. Back-analysis of the test results also indicate that the top-load stiffness inferred from the O-Cell test may be over-estimated due to opposing displacement interaction effects. The conclusion is that actual pile stiffness at the serviceability load may be about 55% of the design estimate. However, pile top settlement is relatively small (i.e. ~ 2% of pile dia.) and the design estimate is considered reasonable in terms of accuracy for geotechnical design purposes.

Poulos H.,Coffey Geotechnics Pty. Ltd
Proceedings of the Institution of Civil Engineers: Civil Engineering | Year: 2010

High-rise buildings are usually founded on some form of piled foundation subject to a combination of vertical, lateral and overturning forces. However, conventional methods for assessing stability may not be adequate when designing such foundations because they tend to focus on resistance under vertical loading. This paper sets out an ultimate-limit-state approach for computer-based design of pile foundation systems for high-rise buildings and provides an example application on a 151-storey tower in South Korea.

Knott D.L.,Coffey Geotechnics Pty. Ltd.
47th US Rock Mechanics / Geomechanics Symposium 2013 | Year: 2013

Three examples of Australian practice dealing with development over abandoned coal mines are presented. Coal mining started in Newcastle, north of Sydney in about 1800 using convict miners. In portions of New South Wales, approval for development over mined areas is regulated by the Mine Subsidence Board (MSB), a government agency that is responsible for repairing structures damaged by subsidence. The MSB is funded by a levy on coal and it regulates investigation and development standards to limit its exposure to claims, a process that provides uniform guidelines for development. Sites above abandoned mine workings were able to be developed by stabilizing the underlying workings by injecting a flowable cement fly ash grout through grout holes drilled from the surface and / or over-excavation. Shafts must also be mitigated. Copyright 2013 ARMA, American Rock Mechanics Association.

Eckersley J.,Coffey Geotechnics Pty Ltd
Australian Geomechanics Journal | Year: 2016

The limitations of our knowledge base result in occasions when "engineering judgement" is required. But what is this, and can it be developed? Engineering and geotechnical training focusses on technical and perhaps managerial aspects but pays little attention to the development of engineering instincts. This paper explores the concept of engineering intuition and suggests directions that may be pursued by (young) engineers to encourage its growth. This is based on reflections of my own experience and is primarily explored and illustrated within a geotechnical context.

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