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UBC Theses and Dissertations

Monotonic and cyclic shear response of reconstituted natural silt Barnes, Daniel Mark


A triaxial apparatus was upgraded and a specimen preparation device was developed to enable monotonic and cyclic triaxial testing of low plastic reconstituted silts. The silt reconstitution technique involves consolidating silt slurry inside a cylindrical split mold, directly on the triaxial base pedestal. The slurry is carefully poured into the split mold using a flexible hose. A vertical load is then applied to slurry using a top cap and loading ram. Loading is applied in an incremental manner and the slurry is allowed to consolidate, creating a specimen firm enough to carry on with triaxial testing. The newly developed silt reconstitution device was verified with respect to specimen uniformity, saturation and test repeatability. Using the new triaxial apparatus and silt reconstitution device, the monotonic and cyclic shear response of Kamloops silt was investigated, contributing to the understanding of the material behaviour of relatively low plastic silt. Silt specimens, initially hydrostatically consolidated to various stress levels, displayed cyclic mobility type strain development during both monotonic and cyclic loading. The specimen preparation technique was capable of producing laboratory test specimens having Skempton’s B values of greater than 0.98, indicating a high level of saturation of prepared specimens. The undrained shear strength measured in undrained monotonic triaxial extension was found to be 20% lower than the undrained shear strength measured in monotonic triaxial compression. This difference is in accord with the stress-path dependency typically found in gravity deposited sediments, and is considered to be due to the anisotropic soil fabric. Liquefaction in the form of strain softening accompanied by loss of shear strength did not manifest in the reconstituted Kamloops silt regardless of the applied cyclic stress ratio (CSR). The cyclic shear resistance of the material was found to be relatively insensitive to the applied confining stress level. The cyclic mobility type stress-strain behaviour was observed in spite of the initial static shear stress bias. The potential for excess pore water pressure generation was observed to decrease significantly with increasing level of initial static shear.

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