Date of Award

2015

Degree Type

Thesis

Degree Name

Master of Engineering Science

School

School of Engineering

Faculty

Faculty of Health, Engineering and Science

First Advisor

Associate Professor Sanjay Kumar Shukla

Second Advisor

Dr Mehdi Khiadani

Abstract

Sand-clay mixtures are commonly used as a liner/barrier material in various engineering applications, such as construction of hydraulic and waste containments. Permeability, compressibility and strength are important properties of sand-clay mixtures and are often required for the design of the liner/barrier of the containments.

In states like Western Australia, which is covered mostly by sandy soils, engineers face difficulties with economically sourcing clays for liner/barrier applications. Any reliable research finding that recommends an optimum clay content to be used with sandy soil can be of significant importance. Such findings for the local Perth sandy soil are rarely available in the literature. Sodium bentonite can be added to Perth sandy soil as active clay in an appropriate amount to create a cost-effective liner/barrier material, especially for landfill applications. Bentonite has been used for such applications in other parts of the world.

In this research, the permeability, compressibility and strength characteristics of Perth sand–bentonite mixtures are investigated to support recommendation for a cost-effective liner material with three different local soils. A series of standard compaction tests, a onedimensional consolidation test for compressibility and permeability characteristics, and an unconfined compression test and direct shear tests for strength characteristics were conducted on nine different sand-bentonite mixtures. The mixtures were formed by mixing local soils, namely brickies sand, plaster sand, and river sand with 5, 10, and 20%, by dry weight, of sodium bentonite.

The test results show that soil permeability and compressibility are greatly affected by the type of soil used in the mixtures. The optimum amount of bentonite for brickies sand, plaster sand and river sand to achieve a permeability of less than 10-9 m/s, which is a liner design requirement, was found to be 5%, 10%, and 10%, respectively. The compression index increases linearly with the increasing bentonite content for any type of sand-bentonite mixture, but the rate of increase is relatively higher when bentonite is mixed with brickies sand. The results obtained from strength tests indicate that the unconfined compressive strength, the cohesion and the Young’s modulus all increase with increasing bentonite content, while the angle of internal friction decreases.

Further, four possible methods, namely Casagrande logarithm of time fitting method, Taylor square root of time fitting method, analytical method and improved rectangular hyperbola fitting, are compared for estimating the coefficient of consolidation of sand bentonite mixture. The analysis shows that the improved rectangular hyperbola method is the most reliable method for calculating the coefficient of consolidation among the four methods.

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