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Design and construction of retaining structures for Lane Cove tunnel
The Lane Cove Tunnel in Sydney connects the M2 Motorway at North Ryde with the Gore Hill Freeway and the Pacific Highway at Artarmon. Design and construction involved about 70 retaining structures which included braced and anchored bored pile walls, soil nailing, reinforced soil wall systems and post-tensioned cantilever walls. Significant challenges related to restricted site access, the need to minimise construction impacts and a tight design schedule.
Rigorous assessment of the effects of new construction on existing structures and construction safety utilised advanced numerical techniques to model ground-structure interaction. This paper discusses various geotechnical issues affecting design and construction, how the design was implemented in the field and documents results of performance monitoring.
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Recent advances in the usage of recycled materials in transportation geotechnics
Priority waste materials currently generated in Australia include construction wastes, demolition wastes, glass fines, waste tyres, plastics, industrial wastes and organic wastes. The increase in generation of these wastes have led to significant research over the past decade on the reuse of recycled waste materials in geotechnical engineering applications. An estimated 7.9 Mt of wastes, which accounts for 36% of Australiaβs current annual landfilled waste, have the potential to be diverted into civil engineering applications, such as for the construction of roads, railways and land reclamation projects. Recycled materials have been evaluated in the laboratory and new specifications successfully developed, to incorporate their usage in pavement geotechnology and ground improvement applications. Recycled materials are increasingly being used in unbound and stabilised pavement applications. In addition, industrial wastes such as fly ash and slag have also been evaluated in recent years as alternative binders to cement in pavement and ground improvement applications. This paper discusses recent advances in the usage of recycled materials in transportation geotechnics, with reference to case studies of recycled materials usage in Australian projects. Ground improvement projects, comprising of the installation of ground inclusions in waste materials, in an international railway and an airport land reclamation project are also discussed.
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An Innovative Approach for the Installation of Vibrating Wire Piezometers
Vibrating wire piezometers, described hence forth as VWPs, are high precision geotechnical instruments installed into the ground to electronically monitor pore water pressures over extended periods of time. These instruments have use in a variety of geotechnical engineering settings such as: slope stability; basement excavation; consolidation under embankments and reclamations; and the performance of hydraulic structures e.g. dams. The piezometric data are useful for the design of these structures and for monitoring the performance during construction and in service. VWPs are traditionally grouted into drilled bore holes in a process that produces waste spoil and requires the use of additional materials for back filling. This paper discusses and reviews two case studies of an innovative, low impact and high-quality approach for the preparation and direct push installation of the VWPs. This installation approach eliminates the production of spoil, is fast and therefore low cost, completed with low impact plant and most importantly has a very high success rate using a locally manufactured push in adaptor and off the shelf VWPs.
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A micromechanics-based approach as an alternative to the experiment to characterise the fatigue behaviour of pavement materials
Pavement materials feature a heterogeneous microstructure, consisting of differently-graded granules randomly distributed in the material domain and/or connected by a binder matrix. This microstructural feature significantly contributes to the complicated fatigue behaviour of the materials when subjected to traffic loadings. Existing experimental methods for pavements have faced difficulties in controlling the material microstructure and its effects on the macro-behaviour. This results in scattered experimental data often observed in the fatigue tests of pavement materials, making it hard to characterise the material behaviour and quantify parameters for practical design. This paper presents a micromechanics- based numerical approach for characterising the fatigue behaviour of pavement materials. This numerical approach can physically reproduce the heterogeneous microstructure of the materials with different gradations thanks to the application of Discrete Element Method (DEM). Moreover, the incorporation of a damage-plastic contact model enables DEM to capture the fatigue behaviour of pavement materials. Through several numerical examples, the numerical approach is shown to predict well the fatigue behaviour and real crack development in pavement materials. Given its better controllable and cost-saving features, this numerical approach can be an effective alternative (to experiments) to assist engineers in the design of road pavements.
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Energy geo-structures in transport infrastructure: Are they feasible?
Ground source heat pump (GSHP) systems use the ground as a source of sustainable thermal energy. This shallow geothermal energy technology has proven to efficiently provide renewable energy for space heating and cooling. While the use of purposely built boreholes is widespread, it is becoming increasingly common to attempt to use any geo-structure in contact with the ground as the ground heat exchangers (GHEs) of GSHP systems. In this way, major capital cost savings are potentially achieved since the highest additional costs associated with geothermal technology are drilling and trenching, already required for structural purposes. In transport infrastructure, sub-surface structures designed for stability are abundant. They can be used to also exchange heat with the surrounding ground, converting them into energy geo- structures. This paper summarises the potential of applying this technology to piles, soldier pile retaining walls, diaphragm retaining walls, slabs, road bases and tunnel linings. These are geo-structures that are commonly found in rail and highway projects such as the Melbourne and Sydney Metro Projects, and the West Gate Tunnel Project to name a few. Detailed 3D finite element models have been developed to investigate the thermal performance of these systems, exemplified herein on an energy wall. The applicability of this technology is discussed for different thermal load scenarios, showing the importance of the thermal load distribution balance. Barriers to adoption are also briefly discussed.
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Geotechnical design and construction performance of abutment modification
Many civil engineering structures rely on geotechnical input to provide practical and innovative solutions, often in the face of uncertainty. In a recently completed major roadway widening project in Melbourne, a geotechnical alternative design was proposed to modify an existing bridge spill-through abutment to improve the functionality of the roadway by enabling the construction of two traffic lanes rather than a single lane proposed in the reference design. The solution involved removing the spill-through abutment and slicing through the counterfort buttress retaining wall and its foundations to form a continuous vertical face, transforming the retention system into a monolithic blade wall laterally supported by soil nails and rock bolts. This paper describes the alternative solution that was adopted and identifies the construction risks that had to be managed during construction. The importance of real-time and continuous geotechnical monitoring as a means to control the excavation sequence and verify abutment performance throughout the construction works is emphasised.
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The Evolution Of Geological Models As An Aid To Geotechnical Stability Analysis, Latrobe Valley
Lignite Mining in the Latrobe Valley commenced in the late 19th Century (Drucker, 1984) and three world scale large open pits continue to operate today. Extensive coal exploration, hydrogeological and geotechnical investigation drilling for over a century, enabled the establishment of desktop geological models. Up until the 1980s these models required extensive manual input and updates were onerous. Due to the extensive data available, as well as a team of State Electricity Commission of Victoria (SECV) geologists, the models were considered reliable and carried a reasonable degree of accuracy, including in areas of geotechnical stability interest.
To facilitate potential expansions in the use of lignite, in 2002 a government led initiative resulted in the creation of the digital Latrobe Valley Regional Coal model (Jansen et. al., 2003). This model relied on data from some 8,000 drillholes including the SECVβs stratigraphic interpretations and coal quality results. This model has since grown in extent to cover the Stradbroke area (in 2008) and the Moe Swamp Basin and Seaspray Depression (2011). Of note is the coarse scale of these models with respect to the lignite seams which required seam definition rules to define the extent of the seams which tend to split at basin margins.
Each of the operating mines has a more sophisticated subset of the model and include hydrogeological and additional structural detail. Such detail is required in areas both within the operational and non-operational areas of the mine, where geotechnical stability carries significant importance. The models allow rapid sectional work providing slope angles of coal seams for geotechnical studies as required. Such studies are valuable in the planning for various conceptual mining and infrastructure projects.
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Integration Of Historic Basements
Basement construction and retention solutions in urban environments are constrained by numerous factors both internal and external to the site. This case study reviews the different challenges encountered at a basement construction site in Melbourne. A detailed review of historic site information provided a basis to optimise the ground parameters and integrate historic temporary works into the retention design. Collaborative working between the lead contractor, geotechnical engineer and structural engineer enabled existing basement structures to be used as temporary and/or permanent works, as well as reducing temporary retention works to provide project cost savings and reduce project risks.
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Effects Of Stone Column Installation
Lateral soil displacements caused by stone column installation can be estimated using analytical methods. These analytical methods have been used to assess lateral movements measured during installation of single stone columns and generated by installation of a group of columns. The analytical methods were able to closely match lateral displacements during installation of single stone columns but were less accurate for group installation. Excess pore pressures generated by installation of the group of stone columns was also measured and the peaks could be reasonably approximated using analytical methods. Installation of the group of columns was also simulated using finite element methods. A numerical model based on in-situ and laboratory test data produced similar results to the analytical methods. Refinement of the parameters to better fit the measured data required a four order of magnitude increase in the permeability. It is speculated that such an increase in permeability is created by fracturing of the soft clay during installation of the stone columns. A finite element limit analysis was performed to assess whether the soft clay would be squeezed into the columns. The results of the assessment suggest that it is unlikely that the soft clay would penetrate further than about 2 rows of stone particles.