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Geotechnical Offshore Site Investigation And Reclamation Design At Port Kembla
Port Kembla is an active seaport situated approximately 90 kilometres south of Sydney. The majority of the current port activities are focussed in the Inner Harbour area of the Port. However, as this is reaching capacity, the port authority is turning its focus onto the planning of the development of the mostly undeveloped Outer Harbour. Stage 1 and 1A (Phase 1) development of the Port Kembla Port Corporation (PKPC) Outer Harbour master plan would create one additional bulk cargo berth and approximately 10 hectares of reclaimed land. In February of 2010, PKPC awarded Snowy Mountains Engineering Corporation (SMEC) the contract to undertake Phase 1 detailed geotechnical site investigation works, and the associated reclamation and berth designs.
The Outer Harbour has been subjected to deposition of materials from five previous disposal campaigns, whereby dredged sediment from the Inner Harbour was disposed of within the Outer Harbour. Underwater containment bunds of uncrushed blast furnace slag were constructed for one of the disposal campaigns, and the contained areas were filled with spoil that typically consists of unconsolidated, very soft, compressible clay. This is consistent with geotechnical interpretation based on site investigation data which found that unconsolidated dredged fill, up to eight metres thick, underlies the majority of the Stage 1A and 1B development, generally thickening towards the east and southeast.
Phase 1 geotechnical design for the Outer Harbour development includes the design of containment bunds and land reclamation design associated with subsequent infilling with appropriate select fill material. Various design options were considered for both the bund and reclamation construction. Instrumentation and monitoring were proposed as part of the detailed design in order to confirm design assumptions and monitor the performance of the reclamation.
As the detailed design progressed, PKPC made the decision that the conforming design, which satisfied the original scope of works and settlement criteria, would not be constructed. Their preference instead was for a reclamation design that eliminated the need for removal of any of the underlying dredged spoil and did not utilise ground treatments other than passive preloading and surcharging techniques. The developed design has since been issued for tender and a constructor selected with construction about to commence.
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Design, installation and verification of CFA piles and common challenges in the Melbourne region
Continuous Flight Auger (CFA) piling is a common foundation type for building and infrastructure projects in and around Melbourne, as well as nationally. The Australian piling market has significant expertise and capability in their design and construction, which has been developed over the past two decades or more, primarily in the building industry. Most of this expertise and experience is held by specialist piling subcontractors. In the building industry, CFA piling projects have been delivered primarily using a design and construct contracting model, where the specialist piling contractor has responsibility for designing, installing and certifying the foundation system. More recently, CFA piling has become popular on infrastructure projects, where responsibility for design, construction and verification involves a broader range of parties, including geotechnical and structural consultants, main contractors and specialist piling contractors. Successful project delivery in this environment requires good understanding and alignment between all parties, and sound design, construction and verification processes. Deficiencies in these processes can lead to conflicts and practical difficulties during the piling works. Further, they can expose designers, contractors and project owners to risks with respect to cost, quality and program outcomes. The geology of Melbourne also presents some challenges in relation to CFA pile design and installation, including a predominance of low strength soils in the Yarra Delta area, deep siltstone bedrock and variable and unpredictable basalt flows. This paper discusses important aspects of CFA piling projects in the building and infrastructure sectors, as well as some commonly encountered challenges in and around central Melbourne. The author endeavours to provide an overview of important aspects of this pile type to assist in broadening the understanding of industry practitioners who are involved in planning and executing CFA piling projects.
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Prediction of collapse potential for silty glacial sand
This paper examines the wetting induced collapse behaviour of three different silty glacial sands from South Australia. Single-oedometer collapse testing was applied to determine the wetting induced collapse settlement. For each soil, three different initial dry unit weights (one close to the field dry unit weight) were used to investigate the effect of dry density ratio. For each dry unit weight, specimens were inundated at varying pressure to investigate the effect of wetting pressure. Dry density ratio, percent of clay fraction, wetting pressure and the initial degree of saturation were found to be the key factors controlling the collapse behaviour of soil. A new empirical equation was proposed to predict the collapse potential of soil depending on the aforementioned factors. The empirical equation gave good predictions for the South Australian silty sand. Verification of the proposed equation was performed using existing data from the literature. The proposed equation gave much better estimates than that obtained from existing prediction equations.
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Numerical analysis of geosynthetics and engineering fill in performance of reconditioned ballasted track
Over the past few decades, geosynthetics have been used extensively during track reconditioning to improve soil stability as they offer many advantages including cost effectiveness, ease of installation and minimal earthworks. Among the wide range of products in the market, geogrid remains the most commonly used geosynthetics for soil reinforcement. The aims of this paper are to investigate the effect of varying subgrade properties on track performance and to examine the effectiveness of geogrids and engineering fill for track reconditioning purposes. In the current study, numerical analyses were conducted using engineering software OptumG2, a finite element program for geotechnical stability and deformation analysis. The results of the parametric study indicated that geogrid inclusion within track substructure has considerable effect on settlement reduction and, in particular, increases the bearing capacity of railway track. The results also suggested that increase in axial stiffness of geogrids has minimal impact on track deformation. The most effective and practical location for geogrid reinforcement was achieved at interface between ballast and capping layers irrespective of the subgrade strength and stiffness. Sensitivity analyses showed that both total settlement and the bearing capacity of the railway track were most affected by the changes in the friction angle of subgrade, compared with cohesion and elastic modulus of subgrade, with or without geogrid reinforcement. The findings concluded that proper design of geogrid reinforcement can eliminate the need for or significantly reduce the thickness of engineering fill for ground improvement purposes.
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Case study: Impact of jet grouted column variability on a base block in sand
To construct an underground rail dump station at a port on a land reclaimed island in Australia, diaphragm walls and a base block designed of overlapping jet grout columns was used, aiming to allow excavation without dewatering. The base block varied between a depth of 8.9 and 19.4 m (surface RL ~6 m AHD) with material mainly consisting of sands. Proximity to the harbour provided a groundwater head boundary, with typical levels of 2 m AHD. Jet grout columns were designed with diameters between 2.1 and 2.7 m and a trial at the site was performed prior to construction. Failure of water tightness tests prior to excavation resulted in a second layer of jet grout columns being installed immediately below the original base block. During excavation of the material within the dump station gaps in the base block led to boiling of the sand, often before the base block level was exposed, preventing further excavation or construction. Ultimately an external dewatering and reinjection system was required to allow further excavation and construction of a concrete base slab on top of the base block. Investigation post construction by PSM highlighted the importance of jet grout column trial interpretation, the influence of column diameter, tilt and position variability and the consequence of small gaps in the base block. Monte Carlo techniques, based on observed as-built column variability, were used to demonstrate the impact of variability on the continuity of the base slab. These indicated that near perfect construction was required if the project objective was to be achieved.
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Preloading Ground Improvement For An International Container Terminal Project At Webb Dock Port Melbourne
In this paper, a case study is presented for preloading ground improvement for an automated stacking container development at Port Melbourne, Victoria, a reclaimed site underlain by high compressible marine clays referred to locally as Coode Island Silt (CIS). The paper has firstly reviewed the site reclamation history, followed by consolidation back analysis using PLAXIS 2D to study the historical settlements associated with the previous reclamation and land use and their effect on the future development with and without the adoption of preloading. A decision was then made to adopt a preloading program that involved the application of up to 5.5 m high compacted earth fill (110 kPa which is equivalent to more than twice of the maximum design load for the containers) for a period of 2 to 3 months, targeting to remove over 40% of the potential total settlement under the container stacking loads. The paper also discusses some of the instrumentation, such as settlement plates and vibrating wire piezometers that was employed to verify the target settlement. The study has concluded that the design intention has been achieved by the completed preloading ground improvement program.
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Nonlinear response of 20 laterally loaded piles in sand
Closed-form solutions and their associated spreadsheet program (GASLFP) were developed by the first author for laterally loaded free-head piles in elastic-plastic media. The solutions show behaviour of a laterally loaded pile is dominated by net limiting force per unit length (LFP) fully mobilised along the pile to a depth called slip depth. They are characterised by three parameters of Ng, αo and n (to describe the LFP) and the soil shear modulus (Gs). Conversely, these parameters may be deduced by matching the predicted with measured response.
To facilitate practical design, in this paper, the input values of Ng, αo, n and Gs were deduced in light of measured response of 20 piles tested in sand. The result allows effect of pile types, installation action, and dry or submerged sand to be clarified. In addition, using analogy to pipeline-soil interaction, a new alternative expression described by the parameters kp, αo and n is proposed to construct the LFP. The use of the previous parameter Ng and the new kp is discussed at length. Critical responses for typical deflection levels have also been provided. This back-analysis is elaborated via three typical cases.
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The design of displacement piles in siliceous sands using the CPT
This paper provides recommendations for the assessment of the shaft and base capacity of driven and jacked (or ‘pressed-in’) displacement piles in siliceous sand using CPT data. The recommendations related to open and closedended driven piles are those proposed by the ‘UWA-05’ method and the rationale behind adoption of the selected formulations for this method is provided. The paper also provides guidance on the assessment of the base stiffness of piles in sand.
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PRB Technology Incorporating Acidic Ground Conditions and Bio-Geochemical Clogging – A Critical Review
Groundwater acidity resulting from pyrite oxidation in acid sulphate soil terrain presents a severe threat to the environment. The exposure of low-lying acidic coastal belts to the atmospheric oxygen, exacerbated by phreatic surface lowering in dry seasons and activities like infrastructure development and agriculture, leads to pyrite oxidation and sulfuric acid production in soil. This paper reviews the challenges posed by acid sulphate soils by emphasising the environmental and infrastructure damage caused by acidic soil leaching into water bodies. Permeable reactive barriers (PRBs) have emerged as a promising method of passive treatment for mitigating groundwater acidity in pyritic terrain. This review mainly focuses on the effectiveness of PRBs in low-lying floodplains by addressing the bio-geochemical clogging that diminishes the reactivity and porosity of PRBs over time. This paper also summarises the numerical methods needed to design PRBs in acidic terrains by identifying gaps in current research that could enhance the accuracy of future PRB designs. This comprehensive review contains valuable insights into the ongoing efforts of addressing the challenges associated with groundwater contamination in regions containing acid sulphate soil.
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Self-boring pressuremeter testing in spearwood dune sands
The self-boring pressuremeter (SBP) offers the possibility of direct determination of parameters for sand in situ that cannot be obtained directly by any other means. The paper presents the results of SBP tests in sand in Perth at two locations: three boreholes in the Perth CBD and three boreholes at a test site in Shenton Park. The tests were carried out in Spearwood Dune sands (at both locations) and in Guildford/Perth Formation sands (in the CBD boreholes). The results presented show that the friction and dilation angles determined from the test are reasonable for the sands investigated. The Ko values obtained from the “liftoff” pressures show considerable scatter but, with no benchmark against which to compare them, it is impossible to state whether they are correct or not. With regard to the stiffness parameters, the results show that there is no simple relationship between small-strain stiffness Go and the larger-strain stiffness Gur measured in unload-reload loops in the SBP. For the tests in the CBD, the tendency observed is that Go is higher for the older Guildford/Perth Formation sands than for the younger Spearwood Dune sands, but the rate of “softening” for the former is greater than for the latter. However, the Spearwood Dune sands at Shenton Park show a much higher rate of softening than the Spearwood Dune sands in the CBD, probably due to partial saturation and/or slight cementation in the former.