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Thesis Format

Integrated Article

Degree

Master of Science

Program

Civil and Environmental Engineering

Supervisor

Sadrekarimi, Abouzar

Abstract

The main goals of this research are to explore the influence of partial saturation and fine content on the shear response of oil sand tailings, to identify the liquefaction susceptibility under different initial states. Monotonic triaxial compression tests were carried out to understand the mechanical behavior of the saturated oil sand tailings with varying void ratios. Then the effect of fine content on the yield and critical shear strength, critical state line, and instability line was evaluated by increasing the fine content up to 50%. The experimental results revealed that the shear strength of the oil sand increases with fine content. The effect of degree of saturation on liquefaction resistance was examined based on the wave propagation theory and correlating the Skempton B with Sr. It is found that the reduction in liquefaction susceptibility by decreasing the degree of saturation is due to the increased compressibility of the pore fluid.

Summary for Lay Audience

Liquefaction is a phenomenon in which the shear strength of sand or silty sand reduces by monotonic, cyclic, or dynamic loading. Landslides, lateral movement, dam failure, settling and tilting of buildings, and failure of waterfront retaining structures are examples of liquefaction triggered by static or cyclic mechanisms. The substantial economic losses, human fatalities, and environmental subsequences result from the failure related to the liquefaction. These failures range from limited sand boils to devastating flow slides based on the extend of liquefaction. Calaveras dam and Merriespruit gold mine tailings dam failure are examples of liquefaction flow failure cases in California and Virginia. The Calaveras dam failure in 1918 was triggered by the monotonic increasing load by rapid construction and resulted in 200 m travel. Also, the flow slide failure of Merriespruit gold mine tailings dam in 1994 by the over steepening released 600000 m3 of tailings flowed for a distance of 2000 m. Several studies have been done on evaluating the liquefaction susceptibility on the saturated clean sand. However, most natural soil contains some fine particles or is partially saturated based on the liquefaction failure case histories. Triaxial apparatus is the most commonly used device for simulating the soil's natural condition in the laboratory. To evaluate the effect of fine content on the liquefaction potential, the sand with different percentage of fines are prepared and tested. Fines can affect the shear behavior of the sand-silt mixture in various ways since they can separate the coarse grains or locate inside the voids between them. The effect of the level of saturation was examined by preparing samples with varying degrees of saturation. The decreased saturation level leads more compressible soil medium and produces suction forces due to the surface tension.

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