Sydney Chapter

AGS Young Geotechnical Professionals’ Night


The Young Geotechnical Professionals’ Night is an opportunity to see four selected presentations by young geotechnical professionals discussing interesting and challenging aspects of their work. After the presentations, you will have a chance to catch up with friends and the presenters over drinks and finger food, and see additional posters prepared by YGP’s. The following presentations will be given during the evening.

Assessment of Sleeving Depths for Piles Adjacent to Future Tunnels

Farzad M Azad

This paper will assess the appropriate sleeving depth for foundation piles for one of the multi-storey buildings at Barangaroo South in Sydney. Building C5 will be located adjacent to the future Sydney Metro Authority (SMA) tunnels. These piles may be installed as close as 1m (including tolerances) from the proposed tunnel extrados. They are 1.2m in diameter and the design working load of the piles is 22,400kN and 20,000kN per pile, for two different sections studied here. To assess the appropriate sleeving depth for the piles, first the effect of proposed tunnel excavation on pile shaft friction capacity and then the effect of pile shaft loading on tunnel lining design have been investigated. An analytical technique along with 2D numerical modelling using the commercial program PLAXIS, has been performed for 6 different cases. The investigations found that, provided that the piles are sleeved to below the tunnel spring line, the construction of the future tunnel is expected to cause only minor reduction in the pile shaft capacity between the tunnel spring line and invert, and will have no impact below the tunnel invert level. In addition, the loading on the piles is found to cause only a small increase to the tunnel lining deformation and loads.

An Experimental Investigation of Mechanical Behaviour of CO2 Saturated Coal Specimins

M. S. Masoudian

To reduce the emission of CO2 into the atmosphere, it is proposed to store CO2 into deep coalbeds which may also enhance the production of naturally-stored methane from coal formations. Many studies have been reported investigating the effect of CO2 injection on the flow properties to provide a means of estimating the recoverable CH4 and storable CO2. However, assessment of the long-term integrity of stored CO2 and the potentially damaging effects of CO2 on the mechanical response of coal have been largely neglected. Understanding the geomechanical response of coalbeds to CO2 injection can be crucial in site selection, in designing and planning CO2-ECBM and coalbed geosequestration operations. To investigate the effects of CO2 adsorption on the mechanical strength and stiffness of coal specimens, a series of triaxial experiments have been undertaken. Over 40 core specimens of Australian black coal from the Sydney Basin have been tested. The behaviour of water-saturated and CO2 saturated specimens have been investigated at confining pressures up to 5.5 MPa at room temperature. Results showed that the strength and stiffness of CO2 saturated specimens are significantly less than those of water saturated specimens.

Performance Evaluation of a 21m Deep Excavation Stabilised by Combined Soil Nails and Anchors – A Case Study

S. Alireza (Sam) Mirlatifi

The design and construction of deep basement excavations in soil requires careful analysis and consideration to the staging and support of the excavation works. In urban environments, these issues are even more critical and the importance of the overall stability and ground deformation becomes paramount. In this paper, case study of a 21m deep excavation adjacent to a 4 story residential building in soil alluviums in Tehran is presented. A combination of high pressure grouted soil nails and anchors was adopted in this project. Finite element and limit equilibrium analyses were conducted for design purposes and, also to predict the performance of this deep exaction and to evaluate the impact of the excavation on the existing adjacent structure. Predicted safety factors using limit equilibrium and finite element approaches are compared in this case study. To ensure the design safety, displacements and anchor loads have been monitored during various stages of the construction. Monitoring results and numerical predictions of displacements and reinforcement loads are in a good agreement. Considering the monitoring results, the performance of the excavation has been satisfactory and practising geotechnical engineers can adopt the presented design methods and construction procedure for safe design and construction of future excavations.

Compaction Trial for Comparison of Impact Rolling and Conventional Rolling Techniques for Large Earthworks Programs in the Pilbara

Jessica Dalton

As part of the development of a project site in the Pilbara, a large earthworks program will take place involving the placement of several metres of fill above the current level. Prior to commencement of production filling, a compaction trial was carried out at the site to compare the effectiveness of impact rolling compaction techniques with conventional compaction techniques. Two different rollers, a 12 tonne impact roller and a 21 tonne single drum vibratory roller, were applied across two prepared fill pads.

Variables considered in the trial included: compactive effort; lift thickness; number of roller passes; and moisture conditioning. Significant geotechnical field and laboratory testing was carried out across the two pads to assess density with depth, prior to compaction and at various stages of compaction. The test methods used included direct density testing (nuclear density gauge and sand replacement methods) and in situ penetration testing (CPT, DCP and PSP). Settlement monitoring was also carried out prior to and following compaction.

This paper presents an overview of the results of the trial in terms of compaction achieved by the impact rolling and conventional methods. The different testing methods used during the trial are also discussed in terms of how well these reflected the achieved compaction. The paper will also discuss potential test methods for fill verification of the large earthworks program, based on the trial results and experience during other earthworks projects.

Engineers Australia members participating in AGS technical sessions can record attendance on their personal CPD logs. Members should refer to Engineers Australia CPD policy for details on CPD types, requirements and auditing guidelines.