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Construction of rock socketed piles in Sydney Sandstone to meet performance requirements
Construction aspects are critical to ensure that the design intent / requirements are achieved through good construction methodology and quality control. This translates into ensuring the pile shaft/sidewalls are to a large extent free of crushed or smeared rock. Similarly, the base should be clear of any debris also. Presence of soft material / debris on the base of the pile will alter the load deflection characteristics.
In order to meet the performance requirements through construction a strategy was formulated. The strategy included an advance programme of proof core drilling, use of appropriate drilling tools, reference to the available site investigation information and full-time geotechnical supervision.
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Numerical modelling of ground loop configurations for direct thermal applications
The rigorous design of direct geothermal heat pump systems that use concrete piles or boreholes as heat exchangers to extract or reject heat with the ground needs a model for the thermal process in the ground, the ground heat exchanger (GHE) and the carrier fluid circulating within. Thermal interference between pipes in the GHE is an important factor which may significantly affect system efficiency. Different pipe configurations including single U-Pipe, double U-Pipe and double cross U-Pipe, are modelled using finite element methods to investigate the thermal interference that occurs between the pipes within the GHEs. In this work, water is the carrier fluid circulating through the pipes and exchanging heat with the ground. Water inlet temperatures and ground far-field temperatures were chosen as being typical for Melbourne conditions. U-Pipes are located vertically in concrete piles or grouted boreholes surrounded by the ground. The efficiency of the GHEs is investigated in heating mode. The results presented confirm the importance of geometry in design and the significant variations in performance that can be obtained using different pipe configurations.
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Coastal rockfall hazard identification, Barwon Heads, Victoria
An investigation of rockfalls at The Bluff, Barwon Heads, Victoria was undertaken as the initial component of a larger Risk Management study. Recent rockfalls are a concern for the management of The Bluff, which is a natural heritage asset and popular tourist destination. Subaerial erosion was found to be the predominant slope forming process with variations in slope morphology dependant on the presence of erosion resistant calcrete capping. Spatial variation of rockfall types is controlled by the orientation of bedding in relation to the slope face, and the development or presence of overhangs. Eight distinct modes of failure were identified. Significant changes in the morphology of the rock mass and sixty-three rockfall events were identified through the analysis of historical photographs, indicating active erosion at The Bluff over the past 100 years. Recent rockfall events have coincided with periods of high rainfall, which has been identified as a major trigger. Rock strength parameters and mechanical properties were determined by laboratory testing and the test results were used to investigate the failure mechanics. Back analysis of failed blocks has shown that that failure is influenced by larger scale rock mass features, rather than rock property strength.
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Soft ground improvement by vacuum assisted preloading
This paper describes the behaviour of soft soil foundation stabilized with vacuum-assisted preloading at the New Bangkok International Airport, Thailand. An analytical solution considering the variation of soil permeability and compressibility and a finite element analysis based on an equivalent plane strain model developed by the authors are employed to investigate the performance of the test embankment. The converted equivalent plane strain parameters are incorporated in the finite element code ABAQUS. The associated settlement, excess pore pressure and lateral movement are predicted and compared with the available field measurements. The data indicate that the efficiency of the prefabricated vertical drains depends on the magnitude and distribution of vacuum pressure as well as on the extent of air leak protection provided in practice. The height of sand surcharge and consolidation time are significantly reduced in comparison with the conventional method of surcharge alone. The effectiveness of this method, its economies and its merit potential are also discussed.
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Ground improvement works for Brunswick Heads to Yelgun Freeway
Brunswick Heads to Yelgun Upgrade of the Pacific Highway, which was awarded as a design, construct and maintain for 10 years project, involved duplicating and reconstructing the existing two lane carriageway to provide four lane carriageways over a length of about 9 km. It also involved conversion of the existing Pacific Highway over part of this length into a service road running parallel to the through-carriageways. The project alignment included cuttings to 30 m depth and embankments reaching up to 10 m over soft ground. There were 13 sets of bridges including the major Brunswick River bridges which had a 10 m high southern approach founded on soft ground. There were two sets of three bridges at Marshall’s Creek and its overflow where soft ground extended to significant depths. The project included 20 retaining walls, several of which were in soft ground areas requiring foundation treatment. Concrete Injected Columns (CICs), which were installed using the Soil Displacement Pile technique (Bauer BG-System), had been adopted at several bridge approaches and retaining walls in order to support the embankments and limit differential settlements to acceptable amounts. This method had significant cost, environmental and programme benefits. This paper will outline the project, the design and construction methodology and performance of the CICs.
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A Novel Multiple-liner Design For Preventing Desiccation Of Geosynthetic Clay Liners
Geosynthetic clay liners (GCLs) covered by geomembranes (GMB) often constitute a major component in barrier systems. They are used in waste containments systems such as landfills, brine ponds and solar ponds. In many of these cases, high temperatures can develop as a result of exothermic biodegradation or direct solar radiation and can cause significant desiccation of the bentonite in the GCLs. In addition, the self-healing ability of bentonite may be compromised by exposure to chemically aggressive permeants that are commonly found in such applications.
A new multiple-liner design is proposed in this paper, with two GMB-GCL composite liners sandwiching one layer of geocomposite (GC). The new design is able to actively hydrate top and bottom GCLs through the middle GC layer with clean water. A set of column model experiments simulating a typical bottom profile under a brine pond were conducted to investigate GCL hydration before and after continuous heating at 78±1oC for 14 days. The results were compared to the more conventional GCL-GMB designs. The findings revealed that the new multiple-liner system speeds up hydration of bentonite in the GCL by a factor of more than 3, increase its water content at the end of the hydration stage by up to 50%, and prevent its desiccation when exposed to high temperatures.
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Limitations On Geotechnical Risk Management: Designing For Resilience
The imprecisions inherent and unavoidable in probabilistically-based risk analysis and management are addressed and shown to be a significant limitation on reliable infrastructure design against the loads resulting from hazard events. The nature of hazard events is outlined and the concept of resilience defined in the context of poorly-quantified and unknown hazards. It is suggested that resilience might be improved by purposefully designing infrastructure to match complex system attributes such as decentralisation, heterogeneity and redundancy. The use of event and effects scenarios in choice of a design event in geotechnical engineering is outlined, and the implications of this strategy explored.