Erosion rate of chemically stabilised soils incorporating tensile stress-deformation behaviour

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Muttuvel, Thevaragavan
School of Civil, Mining & Environmental Engineering - Faculty of Engineering
thesis / dissertation description
Problems associated with erodible soils have been reported in Australia and many parts of the world since the early 1970s. Significant soil loss from embankments, internal erosion and piping are some of the problems that practicing engineers face during the construction and maintenance phase of earth structures constructed with erodible soils. It is therefore necessary to identify appropriate stabilisation techniques to control erosion. This study considers chemical stabilisation as an erosion control method and a rigorous testing program has been conducted to investigate how effectively two chemical agents (general purpose Portland cement and lignosulfonate) control the erosion rate of two natural erodible soils (a silty sand and dispersive clay).In this study, a Process Simulation Apparatus for Internal Crack Erosion (PSAICE) has been designed and built to conduct tests on chemically treated and untreated soil samples. The effect of the degree of compaction and moulding water content on erosional behaviour of soils has also been addressed. In addition, the tensile stress-deformation characteristics of chemically treated soil samples have been investigated using a uniaxial tensile testing apparatus, designed and built at University of Wollongong for this current research study.One of the main objectives was to develop an analytical model for the erosion rate that incorporates the tensile stress-deformation characteristics of the soil. The model has been developed based on the law of the conservation of energy and validated using the results of erosion and uniaxial tensile tests conducted on chemically stabilised soil samples.The results of the tests indicated that the erosion rate changes linearly with the hydraulic shear stress; slope of the line that represents the coefficient of soil erosion. The coefficient of soil erosion decreases, while the critical shear stress increases with an increasing amount of stabiliser, irrespective of the soil type. It was also found that the coefficient of soil erosion of chemically treated soil has a strong relationship with its critical shear stress. Uniaxial tensile tests on chemically treated saturated samples showed that both stabilisers increase the tensile strength with a decrease in the displacement at failure.Model validation demonstrated that only a fraction of flow energy (i.e. efficiency index) is used for the erosion process, and it depends on the hydraulic conditions of flow. Moreover, the proposed model can be used to predict the erosion rate of chemically treated erodible soils, if the tensile stress-deformation characteristics, mean particle diameter, dry density, and mean flow velocity through the crack are known.