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UBC Theses and Dissertations

Macro-scale direct shear device for studying the large displacement shear strength of soil-structure interfaces under very low effective normal stresses. Amarasinghe, Ruslan Shanth


This thesis describes a new macro-scale test device for assessing the large-displacement soil/solid interface shear strength at very low effective normal stresses (3 kPa to 6 kPa). The testing method arises from a need to obtain the interface friction between soils and epoxy-coated pipes under low effective normal stress levels which is an important consideration in the design of partly buried seabed pipelines. The test device is fundamentally similar to the conventional small-scale direct-shear apparatus except for its large footprint that provides a plan interface shear area of 1.72 m by 1.75 m. The device is designed to impart displacement-controlled interface-shearing at displacement rates ranging from 0.0001 mm/s to 1 mm/s and with the ability to reach a maximum interface shear displacement of 1.2 m. The desired normal stress at the soil/solid interface is obtained using surcharge loads externally applied by means of bulk sand or water masses, or both in certain cases. The device is instrumented with pressure transducers mounted flush with the top surface of the solid test surface for the measurement of pore water pressure at the shear interface, in turn, allowing accurate determination of the effective normal stress at the soil/solid interface during shearing. The key features of this device are described, and the device capabilities are demonstrated by testing three soil types (Fraser-River sand, non-plastic silt, kaolinite) on two test surfaces (mild steel, epoxy-coated mild steel) at effective normal stresses between 3 kPa and 7 kPa. Comparison of the test results with available findings from other devices is used to further confirm the suitability of the device for the intended purpose.

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