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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 โcombinedโ 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 โstandardโ. 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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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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Preload Design, Part 1 โย Review of soil compressibility behaviour in relation to the design of preloads
The method of treating soft soils by preloading has been used for over a century, and is still widely used today as one of most common form of ground improvement technique. Yet, every now and again, post-construction settlements have been observed to be more than those predicted after preloading. The author believes, in most cases, the poor preload performance is probably associated with lack of understanding of the time-dependent compressibility behaviour of the soft soils. And in particular, the behaviour of secondary consolidation (or creep) is still not well understood despite extensive research and numerous constitutive models that have been developed. The availability of powerful commercial computer programs does not help if they are used indiscriminately when the fundamental principles are not well understood.
Part 1 of this paper provides a review of the factors that influence creep. The dependency of creep on stress level and stress history expressed in terms of the over-consolidation ratio (OCR) is discussed, followed by a discussion on the commencement of creep. A brief overview of time-dependent consolidation and creep settlement analysis methods is provided, followed by a summary of the preload design approach given by Mesri (1991) that illustrates the possibility of the occurrence of higher creep rate some time following preloading.
In Part 2 of this paper, an analytical approach based on Bjerrumโs (1967) time line model, or principle of โartificial agingโ will be presented for preload design to limit post construction settlement, and a preload design example is discussed to illustrate the importance of geological and stress history on post-preload settlement behaviour.
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Collapsing Cones, Slippery Slopes, Hot Ground, Titanic Topples, Dams and Development
Engineering Geological Challenges and Models for the Active New Zealand Environment
Dr. Warwick Prebble
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Performance of Sewer Pipes with Liner during Earthquakes
Recent earthquakes have shown that liquefaction and associated ground deformations are major geotechnical hazards to civil engineering infrastructures, such as pipelines. In particular, sewer pipes have been damaged in many areas in Christchurch as a result of liquefaction-induced lateral spreading near waterways and ground oscillation induced by seismic shaking. In this paper, the addition of a flexible AM liner as a potential countermeasure to increase sewer pipe capacity was investigated. Physical testing through 4-point loading test was undertaken to characterise material properties and the response of both unlined pipe and its lined counterpart. Next, numerical models were created using SAP2000 and ABAQUS to analyse buried pipeline response to transverse permanent ground displacement and to quantify, over a range of pipe segment lengths and soil parameters, the effectiveness of the AM liner in increasing displacement capacity. The numerical results suggest that the addition of the AM liner increases the deformation capacity of the unlined sewer pipe by as much as 50 times. The results confirmed that AM liner is an effective countermeasure for sewer pipes in liquefied ground not only in terms of increased deformation capacity but also the fact that AM-Liner can prevent influx of sand and water through broken pipes, making sewer pipes with liner remaining serviceable even under severe liquefaction condition.
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Backfilled Quarry Development with Inbuilt Landfill Gas Solution
Backfilled Quarry Development with Inbuilt Landfill Gas SolutionA basalt quarry north east of Melbourne operated for over 30 years from the mid-1960s. Rock extraction occurred to a depth of approximately 28 m below ground level with dewatering. Since operations ceased in 1999, the quarry has been progressively backfilled with variably compacted โclean fillโ until 2017 and the groundwater level allowed to rebound close to its former level. Potential development of the land, for residential or mixed land use, triggered geotechnical and environmental investigations with the objective of identifying and managing below ground issues to support a planning rezoning process. Based on the investigation results, some of the key considerations for future development of the site were settlement of the backfilled quarry, foundation system options across the filled quarry extent and management of landfill gas. Development time, future ongoing management pressures and the need for large scale ground improvement, led to the consideration of a landfill gas control barrier integrated within the engineered fill ground solution, and an on-site trial. This paper provides the findings from the surcharge trial to date to combine the reduction in time to achieve an acceptable settlement of the fill and the management of entrapped landfill gas.
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Geotechnical Challenges of Bridge Approach Embankments and Foundations in Poor Ground – Lessons Learnt from RMS Projects
Dr AHM Kamruzzaman (Zaman), FIEAust CPEng NER RPEQ, Specialist Geotechnical Engineer, RMS
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Probabilities of Failure & Factors of Safety in Geotechnical Engineering
Professor D.V. Griffiths, Colorado School of Mines USA