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Numerical Study Of Boundary Conditions For Solute Transport Through A Porous Medium
A transition region may be defined as a region of rapid change in medium properties about the interface between two porous media or at the interface between a porous medium and a reservoir. Modelling the transition region between different porous media can assist in the selection of the most appropriate boundary conditions for the standard advection-dispersion equation (ADE). An advantage of modelling the transition region is that it removes the need for explicitly defining boundary conditions, though boundary conditions may be recovered as limiting cases. As the width of a transition region is reduced, the solution of the transition region model (TR model) becomes equivalent to the solution of the standard ADE model with correct boundary conditions. In this paper numerical simulations using the TR model are employed to select the most appropriate boundary conditions for the standard ADE under a variety of configurations and conditions. It is shown that at the inlet boundary between a reservoir and porous medium, continuity of solute mass flux should be used as the boundary condition. At the boundary interface between two porous media both continuity of solute concentration and solute mass flux should be used. Finally, in a finite porous medium where the solute is allowed to advect freely from the exit point, both continuity of solute concentration and solute mass flux should be used as the outlet boundary condition. The findings made here are discussed with reference to a detailed review of previous relevant theoretical and experimental observations.
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Transition treatment design for bridge approach embankments – from a practitioner’s perspective
Transition treatments in soft soil are implemented for the purpose of achieving differential settlement criteria between a rigid piled abutment and an approach embankment founded in soft soil. With carefully designed transition treatments, bridge abutments and their supporting piles can be constructed early in the construction program without the need to wait for embankment settlement to conclude – thus, facilitating an efficient construction process.
Methods to reduce or control settlement, include the use of piles/columns in the embankment foundation, and other ground improvement techniques such as preloading/surcharging. Piles/columns are used in varying frequency and quantity within the approach embankment to achieve the desired transitional effect and “protection” for the abutment piles from the lateral movement of the foundation soils. Overburden loads are often transferred to the piles/columns through a gravel mattress embedded with geotextiles, commonly referred to as a load transfer platform (LTP). The design of LTP’s depends heavily on the degree of support provided by the soil matrix surrounding the pile/column treatment.
The success of transition treatments can be measured by the magnitudes of settlement within the transition zone and achievement of differential settlement criteria. Methods to reduce long term creep settlement include the use of surcharging pressures to over-consolidate clay soils. In this paper, the measurement of differential settlement in the form of change-in-grade (CIG), i.e. change of slope between two straight lines, are discussed and clarified – removing some ambiguities and confusion which currently exist in practice.
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Laminated rock beam design for tunnel support
The design and construction of semi flat-roofed tunnels, i.e. with a high arch radius to roof span ratio, using a voussoir beam analogy has been proven successful over time. In spite of such a success, the linear arch theory or voussoir beam analogy has always been subjected to a certain level of scepticism due to some of its perceived limitations. Some of the concerns are related to appropriate design methods for the design of rock bolting of multiple beds/laminations in cases where single laminations are deemed unstable upon excavation or while addressing some adverse conditions. This paper investigates the applicability of an analytical solution of the voussoir beam theory for the design of rock bolts in laminated rock beams which has been confirmed with numerical analysis using DEM (Distinct Element Method) analysis. The proposed analysis method can be easily implemented in a spreadsheet to provide rapid assessments though it is considered only one part of the design process with other potential instability mechanisms assessed using other analysis methods.
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Numerical analysis of the bearing capacity of inclined loaded strip footings supported on sheet pile wall stabilized slopes
In practice, the bearing capacity of a strip footing adjacent to a slope is significantly reduced. This paper aims to control the generated failure mechanism and ameliorate the slope stability, using a sheet pile wall reinforcement technique. A two dimensional finite element limit analysis is used to examine the failure condition, through OptumG2 code. The effect of inclined loading on failure envelopes is investigated, through the average of upper and lower bound solutions. This paper focuses on the estimation of the undrained bearing capacity improvement factor for a given load inclination and slope angle. A new evaluation of the size and shape of failure envelopes is presented. Thus, a comparison between the undrained bearing capacity improvements before and after the sheet pile reinforcement is made, to study the most efficient case. The modification in failure loads are compared with those available in the literature.
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Alternative design approach for soft clay improved by PVDs
In this paper the design procedures for multi-stage construction based on the research know-how described by Rujikiatkamjorn and Indraratna (2009) are proposed. The length of a vertical drain, anisotropic soil permeability and vacuum pressure are considered and a reduction in consolidation time through vacuum preloading is compared to other available methods. Design charts eliminating cumbersome iterative procedures are then developed using the equivalent drain diameter as an independent variable to obtain the relevant drain spacing. The design examples based on the land reclamation project at the Port of Brisbane for both single and multi-stage construction are also given.
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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.
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Opportunities For Sustainable Geotechnical Engineering Practice: Two Case Studies From Australia
Geotechnical design elements are major consumers of energy and natural resources in civil and infrastructure projects. However, by applying appropriate levels of engineering and investigation, opportunities exist for more sustainable and resilient solutions that better understand the ground and geo-structure characteristics. This paper presents two project examples from Australia to illustrate such opportunities.
The first example is a residential complex development project proposed over a reclaimed land with underlying soft marine deposits in Sydney. An advanced site investigation revealed an opportunity to use preload and surcharge ground improvement methodology instead of the initially proposed extensive piled slabs. The earthworks were nearly completed, and geotechnical monitoring confirmed the design assumption. A project-specific earthwork specification was developed, considering the site won material characteristics and performance requirements of different zones of earthworks. Through collaboration between the designer and contractor, most of the site-won material could be used in specified zones of the earthworks on site, with or without treatment, without compromising the performance requirement.
The second example is a major new highway project, where value engineering led to a review of the concept design bridge foundations, retention systems, and site investigation results. Alternative structure types and amendments to the earthwork specification were recommended and justified by the local road authority. The proposed changes significantly reduced the construction cost and carbon footprint of the project, making it viable for ministerial approval. The paper presents a comparison of the CO emissions between the alternative solutions proposed and those initially considered, highlighting the contributions made in these projects to global and local sustainability goals.
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Modelling ploughing and cutting processes in soils
Economic growth in Australia and the rest of the world is linked to the scale of construction and mining, and the amount of earth moved each year in these operations is difficult to fathom. When distributed evenly across the world’s population, each individual moves several tonnes of earth each year. This paper highlights current and future research initiatives within the ARC Centre of Excellence for Geotechnical Science and Engineering (CGSE) aimed at developing rigorous, mechanics-based models for fundamental ploughing and cutting processes in soils. State-of-the-art physical modelling is integrated with the development of new techniques for analytical and numerical modelling to elucidate and predict the full progression of forces and deformations in both two-dimensional and three-dimensional processes. A new analytical model for cutting in dry sand is presented, and preliminary results from numerical and physical modelling are described. The analyses reveal effects that available models fail to consider and illustrate how the development of rigorous models may facilitate improvements in production and efficiency in earthmoving operations.
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The contaminated land industry in Melbourne
Since the publication in Geology of Melbourne (Withers & Lane 1992) there have been significant changes in the assessment, remediation and management of contaminated land in Victoria. These changes have resulted in greater public interest in contaminated land issues, increased regulatory control and, perhaps most importantly, improved technical capability of the contaminated land industry. Specific regulation has also developed around the management of acid sulfate soils.
The purpose of this paper is to outline some of the key changes in the geo-environmental industry since 1992 from a regulatory and technical perspective. Much of these changes have come from significant changes in policy over this period which have been developed in parallel with a growing awareness of the issues presented by natural and anthropogenic contamination of the environment and an increasing awareness of need to protect our environmental resources such as ecosystems, land, surface water, groundwater and the air.
Brumund (1994) in his paper to the First International Congress on Environmental Geotechnics in Edmonton stated:
“Some markets served by civil engineers are relatively independent of regulations, some are influenced by
regulations, and some markets are largely created by and driven by regulations. The field of environmental
geotechnics falls largely in this last category”.The last decade of practice in environmental geotechnics in Victoria has seen the development of extensive policy, regulation and guidelines, to the point where the practice in Victoria is predominantly a regulatory driven industry.
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Designing for unsaturated clay
In most terrestrial near-surface situations the soil is unsaturated. Why is it then that soil mechanics theory developed for saturated soil is being used to interpret soil test results and for the design of footings and earthworks in unsaturated soil? A possible reason is that some of the theory and testing are too complex and time consuming for practical use. This is to be regretted because the attempt to use theory developed for saturated soil for situations where the soil is unsaturated leads to confusion and conservative design. This paper outlines recent findings about those factors that determine the shear strength of unsaturated Keswick clay which occurs in the Adelaide Metropolitan area. It transpires that it is not difficult to determine these factors and hence shear strength. This paper also indicates how to use this information for the design of footings and earthworks.