Influence of boundary conditions on the hydraulic-mechanical behaviour of an unsaturated swelling soil

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Siemens, Gregory Allen
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The hydraulic-mechanical behaviour of swelling clay is examined in this thesis. The study includes laboratory testing and numerical modeling which considers the influence of boundary conditions on the hydraulic-mechanical behaviour of a compacted unsaturated swelling clay soil. The laboratory testing component of this research consists of three (3) series of tests using a newly modified triaxial apparatus on which mechanical and hydraulic boundary conditions are altered during liquid infiltration. Mechanical boundary conditions range from constant volume to constant mean stress and also include constant stiffness which is a spring type boundary consisting of both volume expansion and mean stress increase. Hydraulic boundary conditions include drained and undrained flow into triaxial specimens. The numerical modeling component of this research includes the creation of a new capillary tube model for swelling clay materials and incorporates dynamic changes to the cross-sectional area for flow. Laboratory results are modeled using the capillary tube model, an empirical hydraulic model, D’Arcy’s Law, and in an elastic-plastic context for unsaturated soil. Results of the laboratory and numerical modeling components show that boundary conditions dominate the hydraulic-mechanical behaviour of unsaturated swelling clay soil during liquid infiltration. In particular, a mechanism is shown to explain how hydraulic conductivity of a swelling soil can decrease with increasing water content at constant void ratio. Finally hydraulic and mechanical behaviour cannot be considered separately in swelling materials due to the intimate relationship in their response.
unsaturated, swelling soil, suction, laboratory, capillary tube