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Ultimate Strength Of Steel Screw Piles In Sand
Steel screw piles have been in use for about a decade in Australia, with design strengths up to about 1500kN. Screw piles resist applied loads by shaft friction and end bearing at the helix. However, the end resistance is often limited by the structural capacity of the steel helix plate, resulting in design strength that can be significantly less than the available geotechnical strength of the foundation. The paper presents a method for estimating the base resistance of steel screw piles in sand, which compares well with pile load test data.
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Initiation of Internal Erosion in Earth Dams: A Particle-Scale Computational Approach
Australia is known as the driest populated continent in the world, but with periods of high rainfall and flooding followed by long droughts. Earth dams are the number one supplier of water for irrigation, hydropower, and clean water, as well as the major infrastructures for flood control, amongst other purposes. Internal erosion accounts for about 50 percent of dam failures in Australia and across the world. Such failures could be catastrophic, as they often occur without noticeable precursors, posing significant risks to public safety and downstream infrastructures. In this study, we incorporate the Discrete Element Method (DEM) coupled with Computational Fluid Dynamics (CFD) to simulate soil samples under internal erosion as representative elements for dams. The outputs of simulations are evaluated using a statistical machine learning (ML) method to better assess the triggers of internal erosion based on spatiotemporal patterns in particle-scale and sample-scale parameters, such as particle velocity, particle-particle contact force, and fluid-particle coupling force, as well as kinetic and total energy during the initiation of erosion process. Understanding these patterns and correlations at the particle scale may assist in (macro-scale) engineering monitoring and mitigation strategies.
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An improved approach to site characterisation combining geophysical and geotechnical data
In response to environmental, social and climate change the demand for land and the controls on land use are increasing. Traditional site characterisation methods which incorporate drilling, testing and sampling are energy intensive, logistically challenging and time-consuming. The approach that I propose involves using geophysical technologies as well as geotechnical testing to model and characterise a site.
Improvements in data acquisition and data storage capabilities allow a geophysicist to test, characterise and model a site and report regions for further investigation in a fraction of the time of traditional site characterisation. The process requires the application of an appropriate geophysical investigation with some effective geotechnical drilling, testing and sampling to develop a direct correlation. Direct testing may then be required to confirm model estimations and anomalies.
I believe that a geotechnical professional armed with this simple method of characterisation will be better equipped to target regions that require further testing.
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Optimising Site Investigations using a Risk-Based Approach
Mark Jaksa and Michael Crisp
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Ocean-structure-seabed interaction: O-tube modelling of pipeline stability
A key facility used by researchers in the Centre for Geotechnical Science and Engineering is the set of O-tube flumes established at UWA. These flumes are a unique concept that have been developed at UWA to allow simulation of ocean-structure-seabed interactions using realistic metocean and geotechnical conditions. The large, small and mini O-tube flumes allow seabed flows to be simulated at a range of scales, including full scale modelling of small subsea pipelines. Interactions between mobile sediments and infrastructure can be monitored. This paper describes the O-tube facilities and uses example results to illustrate the range of problems that can be tackled. A key outcome from the O-tube research program has been a new methodology to assess the stability of pipelines on mobile seabeds, which is a common design requirement offshore Australia. This methodology is allowing more efficient and cost-effective design of the pipelines that are the vital arteries of Australia’s offshore oil and gas infrastructure.
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Ground Response Due To Deep Excavations In Sydney Sandstone
A deep basement was recently constructed in Hawkesbury Sandstone for a property development on Sydney’s North Shore located adjacent to critical transport infrastructure. With a depth of over 43m, the excavation is among the deepest basement excavations in the world. This paper presents the geotechnical design challenges, construction outcomes, use of the Observational Method (OM) on the excavation, discusses cost savings through innovative construction and design, and presents applications of smart technologies to instrumentation and monitoring.
When unusual displacement was observed adjacent to the transport corridor due to structural uncertainties and construction activities, the OM and verification process provided a flexible framework within which to reassess ongoing movements and effects on adjacent infrastructure to ensure construction could proceed safely. The case history demonstrates the benefit of adopting the OM for excavations to achieve savings in time and cost, and to react to unexpected movements during construction.
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Vibrocoring As An Effective Combined Geotechnical, Geochemical And Ass Investigation Tool
Vibrocoring has been conventionally conducted by many practitioners using aluminium tube of 50 mm to 80 mm diameter, requiring multiple holes to achieve ‘combined’ investigation sampling targets. Apart from the vibrocorer head itself, the penetration of the vibrocore tubes can be limited by the strength and diameter of the tubes, as well as the ability of the tube cross-section to effectively transmit the vibration energy. The length of the sample tubes is typically limited to a 6 m ‘standard’. GHD has worked together with MDS on a variety of projects, using 100 mm diameter steel vibrocoring tubes, to penetrate up to 9 m depth, through sands of up to medium dense/dense relative density and has been able to penetrate into stiff/very stiff clays for up to approximately 1 m (below other sediments). The use of steel tubes allows penetration where aluminium tubes will buckle, it also provides a more effective transfer of vibration energy (less damped) than for aluminium tubes and the wider diameter makes the sample significantly less prone to jamming on shells or blocking within coarser sediments, which effectively stops further penetration/sample collection. A number of case studies are presented, where geochemical, geotechnical and Acid Sulphate Soils (ASS) samples have been obtained from the same core, and where sophisticated geotechnical tests, including staged triaxial with pore pressure measurement, were possible on the firm to very stiff cohesive materials recovered.
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Groundwater Inflow Assessment For Deep Basement Excavations: A Case Study
Approvals for proposed building developments in Sydney are granted by the consent authority with input on groundwater-related matters from NSW Office of Water. Developments with deep basements require approval for construction dewatering. NSW Office of Water input considers the requirements of the NSW Aquifer Interference Policy, including assessment of the excavation’s “groundwater take” and potential impacts associated with dewatering.
In order to adequately assess the potential impacts associated with construction dewatering, and to design appropriate construction dewatering systems, it is important to accurately estimate groundwater inflow rates to deep basement excavations during construction.
This paper discusses and compares established methods to assess groundwater inflows to deep basement excavations, including analytical, analogue and numerical approaches. A case study for a proposed development in Sydney is used to demonstrate differences in estimated inflow based on these approaches, and highlight the benefits and disadvantages of each approach. Consideration is given to geological structures, basement design, and uncertainty in conceptual models and aquifer parameters that can complicate accurate assessment.