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Geotechnical challenges for on-site wastewater management in the Hunter Region
A large number and growing proportion of both single lot residential and larger scale new developments in the Hunter Region are not serviced by a conventional reticulated sewerage system. In such cases, wastewater treatment, its possible reuse and final disposal, is on-site, where the effluent is generated.
A range of geotechnical factors including the site geology, geomorphology, soils, availability and performance of geo and geosynthetic materials, along with climatic factors, have a bearing on the selection, design, sizing and performance of an on-site wastewater system which will perform adequately and meet regulatory requirements. Geotechnical skills in site and soil assessment are fundamental to and necessary for good on-site wastewater system design and to ensure that the environmental impacts associated with on-site wastewater management are minimised.
The Hunter Region displays a number of challenging geological settings and soil types for wastewater management. These include perched and shallow water tables, sensitive aquifers, floodplains and coastal lake and estuary catchments. Soils include sodic, dispersive and duplex soils and high permeability sandy soils with limited capacities for wastewater assimilation. Hydraulic and nutrient loading capacities of some of the region’s soils are limiting and present a challenge to designers.
An understanding of transport and assimilation of nutrients and pathogens through permeable materials is significant in understanding the potential contribution of on-site wastewater management systems to surface and groundwater contamination and the protection of those sensitive receiving bodies by appropriate design.
This paper reviews the geotechnical aspects of on-site wastewater management in the Hunter Region and illustrates, with a number of case studies, both the problems commonly encountered and their possible solutions.
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Recommended methodology for determination of design groundwater levels
This paper describes a new methodology for the determination of Design Groundwater Levels (DGWL) or “reasonable maximum” groundwater levels required for design of road structures, such as pavements and bath structures. Existing methodologies, are not tailored for road design purposes, nor rigorously defined and suffer from gaps that may potentially result in either unacceptable risks or over-conservatism in road construction. The proposed methodology is based on hydrogeology concepts and incorporates various types of data that are collected through all the stages of a construction project. Application of the methodology is illustrated by determination of DGWL for the Gateway WA project which is a significant freight access road project around the Kewdale and Perth Airport precinct in Western Australia.
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Estimation of drainability and its effect on the design moisture content of base course material
Climate, groundwater level, permeability and drainage conditions play a key role in the determination of the design moisture content of base course material in pavement design. Most of Western Australia (WA) has an arid or semi-arid climate. Therefore, moisture content close to the Optimum Moisture Content (OMC) is usually used for the Design Moisture Content (DMC) for sealed roads. In fact, moisture content is unlikely to be constant due to water penetration from surface failures or unusual water precipitation. Thus the material should have suitable drainability to be able to dissipate possible excess moisture content. The natural material for base course in WA can have a relatively high percentage of cohesive fines content (fraction smaller than 0.075 mm size) that limits drainability. In order to improve estimations of DMC, this paper presents a review of the drainability potential concept and its empirical estimation method. This is followed by the development of an analytical method of drainability potential estimation. The results of the drainability potential using the two methods, applied to common base course materials, are compared with their corresponding design moisture content, as required by material specifications in WA. This comparison provides information to allow a more accurate determination of DMC for the base course material.
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Engineering Geology In Tasmania: A Review
Infrastructure assembled since the European settlement of Tasmania in 1803 has been required to cope with a diverse and complex geology. Tasmania is a relatively small island but the superimposition of a complex structural and climatic history sets the stage for significant problems. These fall into four main categories: fractured and deformed rocks, the notorious and variable Jurassic dolerite, unstable Tertiary rift sediments and Pleistocene valley, slope and glacial deposits. This review offers an outline of how the problems arose, their character and material properties, and the means of resolution, or lack of resolution, past and present.
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Soft Clay Stabilization By Mandrel Driven Geosynthetic Vertical Drains
Geosynthetic (prefabricated) vertical band drains are now considered as one of the most cost effective ground improvement technics in many parts of the world, where construction on soft compressible clays is inevitable. However, smear effects caused by PVD installation (eg. mandrel based), drain clogging, drain kinking and well resistance of long drains retard the excess pore pressure dissipation making these drains often less effective in the field, contrary to expectations. Consequently, the rate of settlement of the stabilised soft clay becomes significantly less than what is expected from ideal drains. This paper addresses comprehensively, the numerical modelling aspects of PVD, and the interpretation of field data taken from several case studies, which elucidate the drain performance under various boundary conditions. Theoretical and finite element modelling details are described based on various research studies, mainly through the authors’ own experience. In particular, the experimental data obtained from large-scale consolidation tests are highlighted and interpreted.
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Characteristics and evaluation of recycled crushed rock in railway subgrade applications
The present research represents several laboratory experiments to evaluate the characteristics of recycled crushed rock (RCR) in railway sub-grade applications. Excessive amounts of construction and demolition (C&D) materials have gone to landfill every year and therefore it is necessary to recycle and reuse to reduce the carbon footprint generated throughout the world. A great way to reuse these materials is to put into operation for new construction projects. Although several recycled materials have been used recently in construction industry, little knowledge and research has been undertaken on RCR, which is generated from construction and housing industries. The RCR has previously been used as a structural element of highway pavements and has shown positive results, where very limited and undefined parameters are available. Laboratory test includes sieve analysis, California bearing ratio (CBR), compaction, Atterberg limit and Repeated Load Triaxial (RLT) tests were carried out on specimens sourced locally in Victoria. This research also investigates the resilient moduli (MR) and permanent deformation characteristics of RCR using RLT equipment to gain a thorough and definite understanding of how the material reacts under cyclic loading due to heavy and continuous cyclic loads on the railway track. A finite element modelling was also developed using laboratory experimental results to compare the permanent deformation obtained from the laboratory and numerical modelling. The physical properties, geotechnical properties and finite element modelling shows that the results were satisfied with the Australian standards and Australian Rail Track Cooperation (ARTC) guidelines for the application in railway systems as sub-grade materials.
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Sydney Symposium 2021
Geotechnical Lessons Learnt – Building and Transport Infrastructure Projects
Andrew Leventhal, Prof. Buddhima Indraratna, Kim Chan, Patrick Wong, Dr David Och and AHM Kamruzzaman
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Shear Strength and Modulus of Mine Waste Rock – Large Scale Laboratory Testing Results
This paper presents the sampling and laboratory testing results of mine waste rock consisting of limestone, siltstone, and intrusive materials collected from the Ok Tedi open pit mine in Papua New Guinea. The laboratory tests included specific gravity measurements, index testing, large-scale direct shear tests using a 720 mm square direct shear apparatus, large- scale consolidation tests using a 550 mm diameter consolidation apparatus, and shear wave velocity tests conducted on compressed waste rock samples. The obtained strength values, as well as small and larger strain modulus values, were subsequently compared with existing literature data from the literature. These findings can serve as a valuable reference for mine waste materials with similar lithology, particle size distribution, and stress condition, particularly in the context of static and seismic slope stability designs.
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Soft Ground Improvement – Issues and Selection
Issues that affect the successful application of ground improvement in soft ground are studied, with emphasis on the design, construction and long-term performance of the improved ground, and recent developments relevant to Australian geotechnical practice.
This paper discusses various technical issues affecting typical soft ground improvement techniques including: densification, consolidation, weight reduction, structural support and chemical treatment. Several factors that can influence the selection of a ground improvement technique, or a combination of techniques, are discussed. Case studies are provided to demonstrate the recent application of ground improvement techniques to the design and construction process.
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Working Towards Net Zero Emissions – Role of Geo-professionals
The global movement in climate change protection is to work towards Net Zero Emissions by around 2050. Net zero emissions refers to reducing greenhouse gas emissions to zero, or as close to zero as possible and offsetting any remaining emissions (e.g. clean energy projects).
This paper outlines some of the steps geo-professionals should take to understand the project Sustainability and Resilience requirements, and areas where we can influence design and construction to meet or exceed those requirements. Sustainability, in relation to geotechnical and geo-environmental work, is an integrated process that balances the social, environmental and financial aspects of planning, design and construction, while managing risk, safety, quality and durability to acceptable standards. Resilience is the ability to cope with uncertain yet extreme events and climate change that may occur over the life cycle of the infrastructure, and to allow expeditious recovery and reconstitution of critical services with minimum impact to public safety and health, the economy, and national security. Geo-professionals are at the forefront of being able to contribute towards sustainable and resilient infrastructure in areas ranging from innovative investigation techniques, use of alternative sustainable resources, reuse of existing foundations, minimising waste, and efficient designs to minimise construction time and materials. Some examples are given in this paper to illustrate where geotechnical designs have contributed to achieving sustainable outcomes.