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AGS Adelaide Symposium 2023
Novel Solutions in Sustainable Geotechnics
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Pull Out Resistance Of Geosynthetic Straps From Shale And Silty Sands
This paper presents results from a study of the pull out resistance of geosynthetic (ParawebTM ) straps from two fill materials. The first is sand with variable silt contents and the second is Ashfield Shale. For both materials shear box tests of the fill material, shear box interface (fill material – geosynthetic) tests and pull out tests have been performed for a range of confining stresses.
There has been evidence of the poor performance of reinforced shale fills in Sydney, but the reasons for this are not well understood and many different opinions exist. These include weathering/breakdown of the shale, wetting/pore pressure development, creep and arching. Tests have been performed to evaluate which of the proposed mechanisms is responsible for the poor performance. It is shown that the tendency for even well compacted shale to compress when sheared contributes to arching, which leads to low pull out resistances. It has been found that when the shale is crushed to <75 m the pull-out resistance is greater than when a uniform material with gravel sized lumps is used. This is explained by the arching mechanism and the impact of the grading on the stiffness, density and compressibility of the fill material.
It is widely accepted that reinforced earth walls (REWs) need to contain ‘good quality’ fill i.e. sands and gravels that are well graded. For example, the RTA QA specification R57 (2007) states that soil properties should be granular and contain less than 15% fines <75 m. Tests have been performed to assess the effects of increasing non-plastic fines content by mixing silt with sand. Addition of silt affects maximum and minimum densities, frictional and dilatational characteristics and the pull-out resistance. It is shown that addition of non-plastic fines significantly improves the pull- out resistance for low fines contents and as further fines are added the pull-out resistance reduces. However, even with 26% fines the pull-out resistance is greater than for clean sand.
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Fibre Reinforced Soils For Geotechnical Infrastructure
This paper presents the results of recent laboratory studies on fibre reinforced soils. Drained and undrained triaxial test results highlight how soil stress-strain behaviour may be altered by mixing with discrete flexible fibres. In triaxial compression a considerable strength increase is induced by the presence of fibres, while in extension the strength increase is very limited. This is attributed to the fibre orientation distribution with respect to the tensile strains developed. Also presented in the paper is a framework for introducing the effects of fibres and their orientation into a constitutive model to describe the anisotropic stress-strain behaviour of fibre reinforced soils. Model simulations of selected test results are shown. Also described are examples of future investigations and trials required to make the soil reinforcement technology ready for use in industry.
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Collaboration Between Industries For The First MRT Line In Malaysia
This paper presents a summary of some of the collaborations that were undertaken to ensure the successful completion of the Klang Valley Mass Rapid Transit (KVMRT) – Kajang Line in Kuala Lumpur, Malaysia. As a developing nation with the will and desire to construct the first MRT Project, the local joint venture company of MMC and Gamuda was presented with many challenges. To start the ball rolling, the team would have to make do with predominantly local resources. To meet the stringent requirements of the tunnelling fraternity and the underwriters, collaboration with the client and upskilling of the local industry players were necessary. While many of the points mentioned herein may be a norm in countries where Metro projects are already mature, the local construction industry in Kuala Lumpur still had a lot of catching up to do. The collaboration with the client, the site investigation contractors, laboratory/ testing agencies and geophysics service providers was instrumental in making the project a success.
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Earthquake Hazard And Risk In Regions Of Low To Moderate Seismicity
Historically building design in many parts of world does not consider seismic loading. While this is clearly not appropriate for regions of high seismicity it is probably sensible for regions of low seismicity. The question addressed by this paper is whether the cut-off level for seismic design as proposed by the US International Building Code (IBC) is reasonable.
This paper presents some key issues regarding the nature of seismic ground motion hazard and how to assess whether it is sufficiently large to require it to be considered in the design of buildings. It begins by summarising some observations from the 1985 Mexico City and 1989 Newcastle earthquakes with regard to building damage and site response effects. These observations are followed by an overview of seismic hazard and risk studies carried out by the author for the United Kingdom, Hong Kong and the Malay Peninsula. These studies were carried out in the early 1990’s, 2000’s and 2008 respectively. Partly because of this range of timing, and the widely different nature of the building stock, the methodologies used for these studies have developed. The underlying results however show that the IBC gives reasonable guidance as to when seismic ground motion can be ignored.
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A preliminary study of strength behaviour of lime-slag treated pyrite bearing soft Coode Island Silt
The prime locations of the central business district of Melbourne are underlain by extensive deposits of a very soft and highly compressible soil, locally known as Coode Island Silt (CIS). This soft deposit poses serious challenges for the design and construction of economic foundations. The conventional practice for almost any construction over this soft soil is to use pile foundations extended to Melbourne mudstone layer situated at about 30 m depth. Results from recent researches on employing soil mixing technique to improve the engineering properties of this soft soil by using different additives have been found to be promising. Pyrite bearing CIS was treated with lime-activated slag of various proportions. Presence of pyrite is responsible for creation of acidic environment through its oxidation and thereby hindering the progress of cementitious reactions. Through experimental study it has been found that providing higher amount of lime can be an effective way of overcoming the adverse effect of pyrite. Initial Consumption of Lime (ICL) test can be a useful tool to determine the minimum amount of lime required for the stabilization to be effective. The results of experimental investigations, consisting of unconfined compressive strength tests and XRD analyses, on soft CIS treated with lime-activated slag are presented in this paper. In addition, the importance of carrying out ICL test for the selection of additive dosage is highlighted by presenting the results of strength tests of CIS treated with lime contents both above and below ICL.
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Design Groundwater Levels
Successful design of structures located within or below the groundwater table requires assessment of the variation of groundwater levels over the design life. Currently the methods used for prediction of future water levels are poorly developed usually relying on extrapolation of a limited period of on-site monitoring or reliance on other historical records that may bear little relevance to the site.
Adoption of overly conservative water levels can have a very significant impact on design and construction costs. Therefore, an accurate assessment is required to achieve a design that achieves the optimal balance between risk and cost.
This paper discusses the pitfalls associated with these methods and presents some examples of failure to select appropriate design groundwater levels. Other methods are discussed than may be employed to provide an alternate and potentially more accurate assessment of design water levels so that the risk of adopting poor design levels may be reduced in the future.
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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.