Electronic Thesis and Dissertation Repository

Degree

Master of Engineering Science

Program

Civil and Environmental Engineering

Supervisor

Dr. Hesham El Naggar

2nd Supervisor

Dr. Abouzar Sadrekarimi

Joint Supervisor

Abstract

A series of cyclic and monotonic constant-volume ring shear tests were carried out to determine the cyclic and post-cyclic response of silts and sandy silts with 25% and 50% sand. The elastic soil behavior at very small shear strain (γ < 10-4%) was investigated through shear wave velocity (Vs) measurements using bender elements at vertical stresses ranging from 50 to 300 kPa, while strain-controlled constant volume cyclic ring shear tests were conducted to establish shear modulus (G) and damping ratio (D) at larger shear strain amplitudes (γ > 0.01%). Liquefaction and strain-softening occurred at excess pore water pressure ratios (ru) between 0.6 and 0.7 associated with cumulative shear strains (γ) of 4% to 6%, after which cyclic mobility failure ensued with very large shear strains and excess pore water pressure ratio (ru > 0.9). The test data indicated that existing field CRR-Vs1 correlations could underestimate the liquefaction resistance of soils with fine content (FC) ≥ 50%. It is found that Vs and the maximum shear modulus (Go) significantly decrease with increasing void ratio. Vs is also found to vary with the effective overburden stress to the power of 0.31 - 0.34 for all silt and sandy silt mixes. The results show that while G decreases with increasing γ, D increases with increasing γ only up to γ < 1%, beyond which it exhibits a decreasing trend. The test results further show that dense samples showed higher post-liquefaction undrained shear strength. In addition, silt and sandy silts exhibit strain hardening behaviour during post-liquefaction monotonic shearing. However, the same soil exhibits strain-softening behavior under monotonic shear loading when the pre-cyclic initial stress condition is re-established.

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