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Shale, salinity and groundwater in Western Sydney
The Wianamatta shales, though best thought of as leaky aquicludes, do include scattered zones of fracture porosity within the weathered shale and soil profile, and also at depth in the unaltered shale bedrock. The water within these fractures is generally saline, typically in the range 5,000-50,000 mg/L. The bulk permeability, like the salinity, is extremely variable, typically 10-7 to 10-9 m/s (1-0.01Lu) in fresh shale and 10-6 to 10-9 m/s in the weathered regolith. Although the shales have no value as sources of groundwater, they do present a hydrogeological nuisance. They are associated with surface salting in parts of western Sydney and eastwards to Lakemba. Salt rises with groundwater along semi-permanent watercourses such as South Creek and Second Ponds Creek, which are the lowest parts of their landscapes. Deep weathering zones and enhanced fracturing along lineaments may be significant in bringing this saline groundwater into the creek beds. However another important process in land salinisation is considered to be throughflow parallel to the ground surface and well above the water table. Much salt is believed to be stored within the soil B-horizon, which may contain 30-50 tonnes per hectare; it is added to by infiltration and depleted by throughflow and by deeper percolation to the water table. The probable source of this salt is not seawater trapped in the pores of the shale, which is non-marine, but rather windblown aerosols. These annually deposit between 20 and 200 kg of salt per hectare in western Sydney, which largely accumulates in the clay subsoil below the root zone.
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Meeting The Challenges Of Complex Excavation Interactions
Design of buildings on and around existing underground infrastructure is becoming more and more necessary as land within the Sydney CBD and surrounds becomes a greater commodity and below ground space is being further utilised. In mining, many underground mines need to go deeper to be economically feasible, experiencing higher stresses and challenging conditions than ever experienced before in addition to complex geological settings with significant three-dimensional effects and multiple mining fronts. As a result, such complex and dynamic environment poses significant geomechanical challenges for the planning and design of such projects. The successful design of such projects is therefore fully dependent on a good understanding of what generates the complexity and the consequent impacts. Forecasting and predictive analyses are typically not needed for investigating such complexity and targeting cost-effective, sustainable and resilient solutions. Such analyses often involve large scale and complex 3D models that should be combined with experience based design and understanding of the fundamentals. This paper presents some discussions on how to address complexity with 3D modelling and present some modelling techniques that are useful to achieve reasonable results. Examples of model confirmation are also given to illustrate how some degree of confidence is gained based on available monitoring data and/or observations combined with local experience.
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Recent Advances In The Usage Of Recycled Materials In Transportation Geotechnics
Priority waste materials currently generated in Australia include construction wastes, demolition wastes, glass fines, waste tyres, plastics, industrial wastes and organic wastes. The increase in generation of these wastes has led to significant research over the past decade on the reuse of recycled waste materials in geotechnical engineering applications. An estimated 7.9 Mt of wastes, which accounts for 36% of Australia’s current annual landfilled waste, have the potential to be diverted into civil engineering applications, such as for the construction of roads, railways and land reclamation projects. Recycled materials have been evaluated in the laboratory and new specifications successfully developed, to incorporate their usage in pavement geotechnology and ground improvement applications. Recycled materials are increasingly being used in unbound and stabilised pavement applications. In addition, industrial wastes such as fly ash and slag have also been evaluated in recent years as alternative binders to cement in pavement and ground improvement applications. This paper discusses recent advances in the usage of recycled materials in transportation geotechnics, with reference to case studies of recycled materials usage in Australian projects. Ground improvement projects, comprising of the installation of ground inclusions in waste materials, in an international railway and an airport land reclamation project are also discussed.
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Bulli Pass Landslide Risk Management Part 1 – Hazard Assessment
The Princes Highway along Bulli Pass is a narrow, heavily trafficked two lane section of the Princes Highway that traverses steep slopes on a grade of 9H:1V on the Illawarra Escarpment, about 11 km north of Wollongong, and 75 km south of Sydney in New South Wales (NSW), Australia. It is an important arterial road for the northern suburbs of Wollongong, connecting Mt Ousley Road (M1 Princes Motorway) at the crest of the escarpment to the suburb of Thirroul on the coastal plain at the base of the escarpment. Bulli Pass has a long history of landslide and rockfall events, some of which were reported as early as 1890. One of the most significant of these events occurred on 17 August 1998 during a 1 in 100 year rainfall event. The 1998 landslide event comprised approximately 38 debris flows and slides and numerous rockfalls which partially inundated a number of cars and trapped about 15 cars on the pass. More recently, in early 2015, a small rockfall penetrated the windscreen of a car travelling up the pass.
Transport for New South Wales (TfNSW) commissioned an investigation into slope instability hazards affecting the road in late 2011. This was followed in 2015 by a Risk Mitigation Options study and the detailed design of risk mitigation works in 2016. This paper provides an overview of the methods used to investigate hazards and assess risk at the site over a five year period. This has included research into the landslide history, geomorphological mapping, acquisition and review of airborne laser scanning (ALS) data, review of rainfall data and the development of a landslide volume frequency model. The development of this model allowed hazards to be readily communicated and risks to be assessed. The actual design and construction of the Shallow Landslide Barriers and the Debris Flow Barriers that followed on from these assessments will be discussed in a subsequent companion paper.
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A method for the prediction of soaked CBR of remoulded samples from standard classification tests
Many authors in the past have investigated the ability of standard classification tests to provide an estimate of soaked CBR for remoulded samples across a wide range of materials with most classifications limited to fine grained soils with soaked CBR’s < 20. A method of estimating the soaked CBR of a remoulded soil from a PSD test and an Atterberg Limits test has been developed and tested against field data. It is valid for coarse grained or fine grained soils, or mixtures of both, and is not limited by the CBR value. The method also accounts for modified compaction of the material after soaking as the relative compaction prior to soaking did not influence the correlation. The method is based on more than 400 soaked CBR tests in a wide variety of soils from around Western Australia, South Australian and Northern Territory. The method has been compared against the results of soaked CBR test from several locations around the world and found to be comparable. The method is based on the Fine Material Factor (FMF) of the soil which is the product of the raw Plasticity Index and the proportion of the soil passing the 0.425 µm sieve. This method confirms the long held anecdotal evidence that materials with a FMF < 450 are typically suitable for sub-base use and in some cases suitable as base course. A series of correlations have been developed linking FMF and Soaked CBR for a range of MMDD Ratios.
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Technical Note: Regression Analysis of Soil Nailing Parameters Using Finite Element and Limit Equilibrium Methods
With rising urbanization and growing transportation needs, stabilization of soil slopes has become extremely vital to ensure adequate, satisfactory performance and safety. Soil nailing is amongst the most cost-effective methods used for slope stabilization by inserting relatively slender reinforcing elements, mostly reinforcement bars, into the soil slopes at predetermined intervals, followed by finishing up with shotcrete and mesh installation. This study is based on the determination of the most economical nail length pattern for different soil conditions and establishes a trend using a multiple regression technique with nail length as a factor. In this study, conventional design analysis using relevant charts and tables published by the US Federal Highway Administration (FHWA) has been used to design a 6m high soil nail wall which has been further analysed using Finite Element method and Limit Equilibrium method for a range of soil parameters. Based upon the obtained results, a relationship between soil deformation, soil parameters and nail length using multiple regression technique has been derived. The results obtained from the derived relationship were then compared to the relevant literatures and case studies and were found to be in good agreement.
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Piled foundations on the North West Shelf
Woodside jointly owns and is operator of five piled platforms in the North West Shelf (NWS): North Rankin A (NRA, 1984), Goodwyn A (GWA, 1995), Angel (2008), Pluto LNG (2010) and North Rankin B (NRB, 2012). All these platforms have piled foundations in carbonate soils, although none of these foundations are the same. These variations result partly from the differences in soil conditions, but more importantly from the lessons learnt from the NRA and GWA pile installations. This paper will take the reader on a journey through recent time and describe the piled foundations for each platform together with the philosophy behind each design. It is a journey where Woodside showcases that it embraced the unexpected results during the installation of NRA (first experience of cyclic behaviour of carbonate soils) and GWA (deformation to steel driven piles) and developed robust (Angel and NRB) and innovative (grooving of drilled and grouted piles at Pluto) piled foundations for their platforms at the calcareous North West Shelf.
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Unsaturated soil-cement interface behaviour in direct shear tests
A series of interface direct shear box tests are performed between a compacted completely decomposed granite (CDG) soil and cement grout under different matric suctions and net normal stresses by using a modified direct shear apparatus. Axis-translation technique is applied to control the pore-water and pore-air pressure. The behaviour of shear stress-displacement curves of soil-cement grout interface tests is similar to those of soil-soil direct shear tests. Matric suction and net normal stress have significant influence on the hardening-softening behaviour of soil-cement grout interface. The interface-dilation is also greatly influenced by matric suction and net normal stress. The variation of interface shear strength with respect to net normal stress (failure envelope) for different matric suctions is observed as linear. The apparent angle of interface friction and adhesion intercept increase with matric suction. The compacted CDG soil-cement grout interface behaves as a rough interface. The apparent interface friction angles for different suctions are nearly equal to the apparent friction angles of CDG soil under the same suctions. However, the apparent adhesion values are higher than the apparent cohesion values of CDG soil in lower suction range, but are lower in higher suction range. The variation of interface shear strength with matric suction (suction envelope) is nonlinear and δb value decreases with increase in matric suction.
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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 Union’s 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.