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Cost-Effectiveness Of Tailings Dewatering And Stacking
Over the last one hundred years, tailings dams have failed globally at a rate of 2 to 5 per annum. This failure rate is considered unacceptable by the community and by the mining industry. The conventional transport of slurry or thickened tailings and their storage in a tailings dam, requires low capital and operational expenditure, as slurry tailings can be transported by pipeline using relatively inexpensive and robust centrifugal pumps. Recently, the filtration of tailings, their transport by conveyor or truck, and “dry” stacking have been seen as an alternate method of tailings management. However, filtration and dry stacking are considered expensive. Over the full life cycle, including post-closure, of filtration and a dry stack facility, the potential to increase water recovery for recycling and increased options post-closure can lead to a reduction in the total expense of a dry stack facility.
This study aimed to contribute to understanding of the cost-effectiveness of tailings dewatering and dry stacking as a tailings management method. Various tailings samples from different locations and with different characteristics were tested for their filtration potential. The potential for monetary savings through the reuse/recycling of the water recovered from the tailings through filtration was a particular focus. While tailings with higher clay mineral contents had more potential for water recovery than coarser-grained tailings, they were also more difficult to dewater. Tailings with lower clay mineral contents were relatively easy to dewater, requiring a short residence time, leading to increased water recovery and volume reduction potential. The results identified that there is significant potential for water recovery, leading to monetary savings through the reuse/recycling of water, potential for storage volume reduction, and potential for higher value post-closure uses.
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Mixture of soil and flyash as reinforced earth wall backfill
Fill material performance and its interface friction properties with geosynthetics directly affect the properties of geosynthetics in reinforced earth retaining walls (REW). This paper discusses the performance of cohesive soil and flyash mixture as reinforced earth wall fill material. Laboratory experiments using triaxial testing have been carried out to assess the strength property of cohesive soil mixed with flyash. The results indicate that a mixture of cohesive soil and fly ash has higher strength, rigidity and good interface friction. The technical performance of the mixtures conform to the requirements of geosynthetics reinforced earth retaining walls. Thus this composite filling material can be used in regions where specified graded sand is not available or scarce.
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Adelaide Desalination Project – Tunnelling Review
The Adelaide Desalination Project is the most recent major tunnelling project that was constructed in the Adelaide region. The 1.8 billion AUD project was completed in 2011 and has capacity to provide up to 100 GL per year of drinking water for the Adelaide metropolitan area. The major tunnelling components of the project include two subsea TBM tunnels, a cavern containing the intake pumping equipment, associated shafts and marine works. This paper describes relevant design and construction aspects associated with the tunnelling works, including geotechnical conditions, TBM description, precast segmental lining design, marine works and the tunnel to riser cross connections, which required pre-excavation ground treatment measures by pressure grouting.
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Numerical Simulation of the Effect of Lapointe on Saturated Sandy Ground in Re-Liquefaction Events
Laponite is a nanomaterial that can transform the pore water into a viscous gel and continues to harden with time and can recover its strength after liquefaction. Initially, laponite suspension has very low viscosity, so it could be used in passive site remediation to improve the ground in highly populated areas. In this study, a constitutive model able to reproduce the behaviour of both granular and cohesive materials under different loading conditions is calibrated and validated using several laboratory experimental results. The calibrated parameters are then used to simulate the impact of a sequence of two earthquakes on a residential building with a shallow foundation on a loose saturated soil deposit containing sand that was treated with 1% laponite. This study attempts to provide insights on the level of improvement that laponite could provide as a liquefaction mitigation method in real applications and to show practitioners the potential of using this material for remediation purposes.
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The Engineering Geology of the Sydney Region – Revisited
In keeping with annual tradition, on 13 October 2004 the Sydney Chapter of the Australian Geomechanics Society will present its seventh Mini-Symposium, the Engineering Geology of the Sydney Region – Revisited. This volume of Australian Geomechanics Journal is dedicated to the papers that are to be presented at the mini-symposium.
This topic was previously addressed in the well-known 1985 publication on the Engineering Geology of the Sydney Region. Since 1985 the Sydney region has seen significant infrastructure development, including housing and transportation. This development has provided new opportunities for geotechnical practitioners to advance their understanding of the engineering geology and hydrogeology of the region.
The mini-symposium is intended to provide a forum for the compilation of this knowledge. Topics presented in 1985 have been supplemented with recent data and several new topics have been addressed.
Topics include a review of the engineering (Pells) and hydrogeological (Tammetta and Hewitt) properties of the Hawkesbury Sandstone and case histories demonstrating the engineering implications of variability in the Hawkesbury sandstone (Speechley, Walker and Scholey). Och, Pells and Braybrooke have used recent data to compile a map illustrating geological faults and dykes in Sydney CBD. This map will be handed out at the Mini-Symposium and it is hoped that it will be published in an later issue of this journal.
The engineering properties of the Ashfield Shale have been well documented, but the paper by William and Airey provides similar data for the Bringelly Shale, which has received greater attention as the urban development of Western Sydney progresses. Salinisation in the shales has significant impact on the urbanisation of Western Sydney and is discussed by McNally. Hatley addresses the hydrogeology of the Botany Sands.
The characteristics and engineering implications of the regional stress field are discussed in three papers (Pells, McQueen and Walker). Clearly there are differences in opinion as to the best method for making in situ stress measurements and in the equations that best model the stress field. Interested readers are encouraged to study each of these papers to understand current limitations of stress measurements and predictions.
The convenors acknowledge the contributions made by the authors and the great efforts that have been made to present information that reasonably represents the current state of knowledge. In addition, thanks are extended to peer reviewers, nominated by the authors, who have provided valuable critique.
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Pilbara Cenozoic detrital sequences and associated geohazards
This paper presents two potential geohazards associated with Cenozoic detrital sequences in Western Australia’s Pilbara region.
The first considers carbonate rich calcrete layers, often reflecting the position of historic and current water tables. Observations of geochemistry of the calcrete layers compared with textural features in the resulting rock suggests a link between CaO, MgO and Loss on Ignition (LOI) abundance and the likelihood of cavities existing.
Geohazards in the form of sinkhole or doline formation may result from changes to groundwater by dewatering for mining or town-water extraction. Contributing factors that increase this likelihood are high water flow, presence of dispersive soils in the blanketing layer, a geochemical signature of >20% CaO in the calcrete and commensurate thicknesses of the calcrete layer (and potential void space) and the blanketing layer.
Relic rock slides have been recognised in several detrital valleys in the southern Pilbara and represent the second potential geohazard. The slides appear to represent a specific marker horizon in the detrital stratigraphy, attributed to a high rainfall, global warming climatic event in the Miocene. The slides consist of large rafted slabs/blocks of Archean bedrock with lesser cobbles and clasts of high strength rock. The voids between blocks are infilled with high plasticity, firm to hard kaolinitic clay, thought to be derived from subsequent lacustrine deposition. The preserved unit thickness varies from 10 to 80 m and can be buried by over 100 m of younger detritals.
The slides present a unique geohazard to mining operations, not simply due to the variability in rock mass strength which can impact slope design. A high variability in void and matrix size and distribution is noted, though size and distribution of these zones is typically too small to be “mapped” by infill drilling. The size is however sufficiently large to cause trafficability issues on haul roads.
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Coefficient of permeability of bentonite and bentonite-sand mixture
Bentonite is one of the essential materials involved in the disposal of highly toxic chemical and radioactive waste in deep underground facilities. Bentonite is often a key component of the engineered barrier system for high level waste or spent fuel disposal and has a wide range of application, increasingly in the area of environmental management. The coefficient of permeability of bentonite and of a mixture of bentonite and sand is an essential parameter in the design of any type of waste disposal facilities. A series of standard and high pressure consolidation tests have been performed using different liquid limits for bentonite and bentonite-sand mixtures in order to observe the coefficient of permeability derived from consolidation theory. The coefficient of permeability has also been measured by the falling head method. It was found that the permeability varied at the same void ratio due to the use of a different method of computation. The liquid limit of the bentonite and the content of sand in the bentonite-sand mixture played is a key component in the coefficient of permeability.
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A developed analytical model to predict axial load along a fully grouted rock bolt
In recent years fully encapsulated rock bolts have become a key element in the design of ground control systems. The main reason is that they offer maximum shear resistance to bed separation. In this research, the load transfer capacity of fully grouted bolts is evaluated analytically both using an end plate and without an end plate. The bolt and surrounding materials were assumed as elastic and elastoplastic materials respectively. The load transfer mechanism of a fully grouted bolt is a function of some parameters, such as bolt length, shear stiffness of interfaces, in situ stress, face plate and distance along the bolt. These factors were analytically evaluated. Finally the load along the bolt was predicted in different surrounding rock characteristics.
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Application Of Dynamic Compaction In Reclaimed Roads
Pavement layers are systematically constructed as engineered fills with specified properties and criteria; however these well built layers may be underlain by loose saturated subgrades that, if not treated, may be subject to undesirable and damaging deformations. This may be especially true for roads that are constructed on reclaimed land.
Dynamic Compaction is a ground improvement technique that can and has been effectively utilised for treating thick loose layers of saturated in situ or reclaimed granular soils. In this paper, the application of Dynamic Compaction for improving loose sub-grades will be discussed using three case studies. The case studies have been specifically selected in a manner to demonstrate the applicability of this technique to hydraulic fills and truck dumped fills, to very large projects such as the 900,000 m2 Abu Dhabi Corniche, to moderately large projects such as Marjan Island Main Road corridor and to relatively small sized projects such as the 10,000 m2 approach roads of Reem Island Causeway. The projects can be in undeveloped locations or in urban areas.
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WA Symposium 2021
Geotechnics in Mining & Infrastructure