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Towards A Resilient Design: L-shaped Barrier-impact Load Modelling On Reinforced Soil Wall Structures
It has always been a challenge to model the effect of crash barrier loadings on Reinforced Soil Wall (R.S.W.) structures due to the complexity of their design and the manner in which the load is transferred through each soil reinforcement layer of the R.S.W. structure. Current design practices in Australia rely heavily on the designers experience and the individual knowledge the impact crash barrier loadings have on the R.S.W. structure. Each designer has an individual approach to the same problem. Relevant codes do not adequately cover this issue and leave it up to the designer‟s experience. This paper outlines and discusses a design beyond the current codes and how codes and standards can be enhanced. There is a clear necessity to provide a systematic, well proven and tested approach to the manner in which the loading on the R.S.W. structure from the crash barrier is interpreted, modelled and analysed.
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Underpinning the Concord Road Bridge under traffic: Westconnex M4 East Project
WestConnex is the largest transport infrastructure project in Australia. It is part of the Australian Federal Government and New South Wales Government’s efforts to ease congestion on Sydney’s roads by widening existing motorways and constructing new tunnels and bridges. M4 East is the section of WestConnex which extends from Haberfield to Homebush and includes the new Concord Road Interchange (currently under construction). The Concord Road Interchange is a complex junction of new bridges, cut-and-cover tunnel portals, retaining walls, widening and altering the alignment of the existing M4 Motorway lanes. Part of the works involves altering the alignment of the eastbound and westbound lanes under the existing Concord Road Bridge. To facilitate these works, the bridge needs to be underpinned with permanent support. The existing bridge abutments are founded on piles which are to be supported on a rock ledge permanently supported by rock bolts and prestressed ground anchors. Further, it is a requirement of the project that the Concord Road Bridge remain open to traffic for the duration of the works. Tight deflection criteria were imposed due to structural requirements at expansion joints. Additionally, the existing Concord Road Bridge was designed and constructed in the 1980s and there was limited information on the ground conditions and as-built founding levels of the bridge abutment piles. These factors, in addition to the requirements for working with low headroom under the bridge, were some of the key challenges during the detailed design and construction support of the works. This paper focuses on the methodology that was adopted to address these challenges during the design and construction phases of the project.
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Understanding The Hydrogeology Of A Bauxite Residue Disposal Area
Worsley Alumina Pty Ltd (WAPL) has bauxite mining and refining operations in the Darling Range, near Collie, Western Australia. Bauxite ore refining residue (bauxite residue) is a waste product from the refining of bauxite ore to alumina.
Bauxite residue is a by-product of the Bayer process in which bauxite ore is physically and chemically transformed to extract alumina, leaving a viscous slurry by-product. The bauxite residue is dewatered to give a slurry of approximately 62-64% solids. The solids consist of combined sand and fine silt to clay sized fractions, of which iron (oxy) hydroxides are the dominant mineral. Before and after drainage, the residue remains alkaline, sodic and saline. Consistent with residue chemistry, the drainage liquor is alkaline, saline and contains humic substances.
Environmental legislation demands safe containment of the bauxite residue, which in this case is achieved by deposition into large dams, known as bauxite residue disposal areas (BRDAs), situated within the refinery lease. Worsley Alumina is legally bound to develop a decommissioning plan for their BRDAs. One BRDA in particular (BRDA1) is approaching decommissioning stage. A sound knowledge of the hydrogeology of this BRDA is essential for the development of a satisfactory decommissioning plan.
When BRDA1 is closed and rehabilitated, it will be capped with between 300 to 500 mm of soil and re-vegetated. An interception drain and capillary break will underlie the soil cap, so that it will be non-infiltrating (rather than “impermeable”).
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Settlement Of Soft Marine Sediments At Sydney Airport
The paper reviews the historical development of the western area of Sydney Airportand particularly the early soil investigations to determine the deformation characteristics of the soft clay which underlies the aprons and terminal. It also looks briefly at the settlement of the aprons over a 20 year period to ascertain whether the movements which are being experienced are fundamentally due to consolidation or creep. Finally, it presents some selected data on settlement and creep coefficients derived from recent testing.
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Forensic investigation of subsidence to dwelling, December 2007
Investigation of house subsidence is always fraught with difficulty, because one doesn’t ever know the full information of the foundation soils, the method of construction or the quality of construction. This report illustrates the importance of undertaking a desktop study and obtaining the origins of the soils to confirm the bore hole logging in order to obtain a correct diagnosis of the likely cause of subsidence.
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Brown coal open pit, Yallourn Eastfield, Victoria, FLAC modelling: Morwell River diversion channel-southern batters buffer width
Yallourn Mine, 130 kilometres south-east of Melbourne, supplies brown coal to Yallourn W power station which generates 22% of Victoria’s electricity. The mine is bounded to the south by a man made diversion of the Morwell River, constructed in the 1980s. The initial geotechnical designs located the mine batters 300 m from the river diversion. The worst case scenario from the initial geotechnical modelling was that, if the mine was excavated too close to the diversion, mining induced strain could cause cracking of the diversion which in turn could induce high water levels and failure of the mine batters, potentially leading to catastrophic failure and uncontrolled flow into the mine.
When the mine had developed to total depth it became clear that the actual movements and ground strains were significantly less than previously predicted and that there was an opportunity to reduce the buffer width and increase coal reserves. In the recent past, numerical modelling has been recognised as a powerful tool for efficient analysis and economical design in Civil Engineering projects. In 2000 further analysis was carried out using the limit equilibrium inhouse program (BSTAB) in conjunction with numerical analysis (FLAC). This analysis resulted in a reduction of the buffer width by approximately 50% and enabled deferral for approximately 20 months of major expenditure associated with moving the river to access the coal beyond the river diversion. This paper discusses the results of the stability analysis and model calibration and compares subsequent ground movements against the model predictions.
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Probabilistic risk assessment of mine subsidence
Instability of coal pillars within disused underground mines is an important cause of mine subsidence affecting surface developments. Uncertainty and variability of materials, dimensions and loads affects our ability to assess the stability of these coal pillars. Traditionally, these parameters have been quantified using a deterministic approach. Variables affecting coal pillar stability were probabilistically analysed to determine the factor of safety and probability of failure. Two case studies in the Newcastle region were undertaken in order to simulate real situations. There are two types of uncertainty that need to be modelled: aleatory and epistemic. Aleatory uncertainty is ‘random’ uncertainty or natural variability. Epistemic uncertainty is uncertainty due to the lack of information. The probabilistic risk assessment method used in the case studies provided an assessment of aleatory and epistemic uncertainties. In the assessment of the stability of pillars in old abandoned workings, both types of uncertainty are encountered. Hence, the UNSW Pillar Design Method under-estimates the probability of failure as it ignores epistemic uncertainties of old pillars in abandoned mines. It was also found that there is no direct relationship between factor of safety and probability of failure. It was revealed that the level of uncertainty can have a significant impact on the probability of failure of a section of workings. The results of this study may lead to a requirement that developers use probabilistic methods to verify that proposed developments are subject to an acceptably low risk of subsidence damage.
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Ok Tedi Crusher Replacement Project: The Geotechnical Challenges Of Constructing Infrastructure On Top Of Soft Tailings In Remote PNG
The Ok Tedi mine in Papua New Guinea needed to relocate their crusher infrastructure prior to an open pit cutback, and several project requirements and constraints including steep terrain and difficult time frames drove it to be built over the top of mine processing waste (tailings) up to 30 m in thickness. Consequently, geotechnical aspects of the project were a significant part of the design process and governed many of the construction decisions. This paper focuses on the consolidation and shear strength parameters of the tailings, and how the model evolved from an early concept, into one informed by targeted site investigations. Ultimately, loading trials on site with careful monitoring of settlement and pore pressures allowed the geotechnical model to be verified and refined based on actual field performance. It also presented a good opportunity to reflect on the influence and benefit each site investigation had on the geotechnical model and the resulting design decisions. The final part of this paper reflects on the overall design process, construction outcomes and lessons learnt.