Electronic Thesis and Dissertation Repository

Degree

Master of Engineering Science

Program

Civil and Environmental Engineering

Supervisor

Timothy Newson

Abstract

After the Great East Japan Earthquake of 2011, nearly 24 million tons of disaster debris such as concrete products, natural and polymeric fibres, and tsunami deposits remained on the coast of Japan. Much of this debris was recycled and repurposed in engineering projects such as embankments, park restoration, and agricultural field restoration around Tokyo Bay, one of the hardest hit regions of the country. Such a major disaster developed a need for the stabilization of the liquefaction susceptible regions of the reclaimed Tokyo Bay coastline. This thesis specifically focuses on the stabilization against liquefaction of Toyoura sand with the typical silt contents found in the Tokyo Bay region using polyvinyl alcohol (PVA) fibres and Ordinary Portland Cement (OPC). A link between the large strain static and dynamic behavior of the silty sand and the microstructural elements controlling the mechanical response of the amended soil was developed.

On a macro scale (Rowe cell, bender element, & cyclic triaxial tests), trends based on cement content, fibre content, silica flour content, and cyclic stress ratio were developed to aid the prediction of the mechanical response of the soil mixture. On a micro scale (SEM and CT scans, mercury intrusion porosimetry), the pore structure, soil structure and soil fabric were visualized to understand the mechanisms underlying these trends. Results from the many tests performed confirmed that the addition of polymer fibres and cement improve the liquefaction resistance, undrained shear strength, and stiffness of silty and clean Toyoura sand. In general, the results suggest that the addition of silica flour is beneficial until a threshold percentage of 28-35% is reached, after which the soil becomes mechanically unstable and more susceptible to static and cyclic liquefaction. The addition of 0-2% fibres provides minimal improvement in all tests. Cement, as expected, improves the soils stiffness and liquefaction resistance proportional to the addition percentage.


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