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Back analysis of Lower River Murray riverbank collapses
Riverbank collapses in the Lower River Murray threaten public infrastructure, private property and the safety of river users, and also provide significant challenges for environmental and river management. According to the inventory of the South Australian Department of Environment, Water and Natural Resources (DEWNR), between 2007 and 2010, 50 riverbank collapse-related incidents were reported at four very high risk sites: East Front Road, Mannum; Woodlane Reserve; River Front Road, Murray Bridge and White Sands. The objectives of this paper are to: (i) model four known and representative riverbank collapses at these four sites and (ii) determine the soil shear strength properties by undertaking back analyses. Adopting a GIS framework incorporating light detecting and ranging (LIDAR) digital elevation models (DEMs) and high-resolution aerial images, four cross-sectional models have been accurately established based on the examined historical collapses. Slope geometries have been determined using topographic information obtained from the DEMs. Finite element analyses based on a transient water model have been adopted to simulate the response of pore water pressure under dynamic variations of rainfall, evaporation and river level fluctuations. The limit equilibrium method has been used to undertake the slope stability calculations. The model results, which agree closely with the findings of historical incidents, demonstrate the efficacy of the framework and the accuracy of the predictions.
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Use of temporary anchors in reinforced soil wall construction for the M4 Motorway widening
The M4 Motorway has in excess of 100,000 vehicle movements per day with the projection exceeding 150,000 vehicle movements per day by 2030. To facilitate the projected traffic flow increase, the M4 Motorway has been upgraded by adding an additional lane in each direction (eastbound and westbound) to the existing three lanes. The upgrade comprises widening a 7.5 kilometre section of motorway between Parramatta and Homebush including the construction of 2 kilometres of viaduct with 49 spans, 3 bridges and 24 retaining walls (including RSWs, soldier pile walls, soil nail walls and reinforced concrete walls).
This paper focuses on the sections of motorway widened using Reinforced Soil Walls (RSW) and presents a case study of the use of temporary Platipus anchors, to retain up to 9 metres of existing engineered fill embankment of the motorway. The construction of the RSWs required excavation of the existing motorway embankment at between 45ยฐ to 75ยฐ for excavated heights typically between 6 metres and 9 metres. Platipus anchors were selected in preference to soil nail or sheet pile solution to increase the stability of the steep temporary batter, expedited the excavation process, reduced the amount of excavation of the embankment and reduce the total construction cost. The design considered the stage excavation process and ensured adequate factor of safety at each stage of the excavation process. In addition, the design confirmed that the settlement of the existing M4 pavement immediately adjacent to the excavation was within tolerable limits.
The paper provides discussion on the feasibility assessment of the use of the โPlatipusโ anchors and the design undertaken for the temporary retention system. It also provides a discussion on the installation process for the anchors, anchor testing undertaken, instrumentation and monitoring; and construction challenges for integration of the temporary support into the permanent works.
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Effect Of Enhanced Biodegradation On Settlement Of Municipal Solid Waste Landfills
Recent studies of municipal solid waste landfills have revealed the influence of biodegradation upon secondary settlement. Modern landfills, however, are designed with efficient containment systems which minimise moisture ingress and thereby reduce leachate and gas generation. The shortage of moisture means that these containment systems delay decomposition and stabilisation of waste. An alternative approach is to enhance biodegradation by designing and operating landfills as bioreactors. Leachate and gas are then produced during the early stages when the containment system is new and risk of failure is low. Additionally, accelerated stabilisation allows earlier re-use of the site. This paper describes an investigation conducted in a full-scale bioreactor cell at the Lyndhurst Landfill in Victoria, Australia, to demonstrate the effect of enhanced biodegradation upon secondary settlement. A hyperbolic settlement model is used to quantify the acceleration of settlement due to enhanced biodegradation and to predict the continuing settlement-time relationship.
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Quaking with Fear
Michael Harbison, Mike Griffith, David Love, Lisa Moon and Peter McBean
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Sustainable Choices In Geotechnics: A Case Study of Quarry to Parkland Conversion
Sustainability and sustainable development are broad concepts, and there is a growing imperative to both define sustainability, as per the 17 goals of the United Nations Division of Sustainable Development Goals (DSDG), and to regulate compliance with sustainable practice, such as the European Unionโs Corporate Sustainability Reporting Directive. The geotechnics practice, which is literally at the ground level of design and construction, has many opportunities to consider, develop and drive sustainability within our industry. This paper presents a case study of a quarry to parkland conversion project in suburban Sydney where sustainable practice was considered at every stage, from material reuse of existing fill to alternative means to reducing rock fall risk without installing support structures. The case study demonstrates how elements of sustainable practice in geotechnical engineering and engineering geology were achieved through comparison with select goals as published by the DSDG. Comparisons and contrasts are also made with other projects where perhaps a sustainable outcome could not be achieved due to factors such as existing Standards or time constraints. The paper summarises some of the difficulty of taking sustainable theory into practice and highlights how sustainable construction is often linked to the most economically viable design and maintenance solution. It is hoped that this paper will add to the growing industry knowledge of sustainable geotechnics in practice and provoke discussion of how to incorporate sustainability within the context of our current framework of Standards and standard industry good practice for design.
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The hydrogeological significance of fractures within a weathered rock catchment
Worsley Alumina Pty Ltd (Worsley) operates a bauxite refinery on a lease area occupying the upper reaches of the Augustus River catchment in south Western Australia. This paper presents the results of site characterisation investigations to improve the understanding of the hydrogeology of the study area. Investigations concentrate on the southern portion of the site where sufficient drilling and monitoring data are available to assess the hydrogeology.
Investigations have highlighted the presence of both porous media aquifers within the weathered profile and fractured rock aquifers within the basement rocks. A combination of barometric efficiency measurements and detailed groundwater level measurements has highlighted a strong connection between these aquifers. This connection is thought to be due to the presence of fractured quartz veins found along the margins of dolerite dykes. The results of this investigation have shown that fractures are an important component of the hydrogeology of the Augustus River catchment, which is an example of a weathered rock catchment.
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Development of Horizontal Soil Mixed Beams as a Shallow Ground Improvement Method Beneath Existing Houses
Following the 2010-2011 Canterbury Earthquake Sequence (CES), the vulnerability of residential houses in some areas of Christchurch to liquefaction-induced damage was realised. As a result of the ground surface subsidence caused by the CES, the liquefaction vulnerability has also increased in some parts of Christchurch (Russell et al., 2015). The liquefaction-induced damage resulted in a large number of residential houses in Christchurch that were uneconomic to repair. They are being demolished and rebuilt on stiffer and stronger foundation systems and in some areas which are particularly vulnerable to liquefaction, the stiffer and stronger foundation systems are being used in conjunction with shallow ground improvements. There are also a large number of houses that have liquefaction-induced damage, but are economic to repair. Until recently there was no practical ground improvement solution that could be economically constructed beneath existing repairable residential houses to decrease their liquefaction vulnerability. However, during a shallow ground improvement trial research project, commissioned by the New Zealand Earthquake Commission (EQC) in 2013, a method was developed to improve ground beneath residential houses, known as Horizontal Soil Mixing (HSM). HSM involves the mechanical mixing of injected grout into in situ soils using a modified directional drill and a specifically designed soil mixing tool to construct a series of HSM beams to improve the thickness and stiffness of the non-liquefying crust and decrease the vulnerability of the existing house to future liquefaction-induced damage. This paper describes the development of the HSM construction methodology, including constraints and issues that were encountered and overcome.