Effects of Strain History and Induced Anisotropy on Reliquefaction Resistance of Toyoura Sand

Recent earthquake events have indicated that liquefaction histories can greatly affect the reliquefaction resistance of saturated sandy ground. This paper reports a fundamental experimental study of medium-dense/dense Toyoura sand with a relative density of 70% using a hollow cylinder torsional shear apparatus (HCTSA) to provide a better understanding of the integrated effects of strain history and soil fabric on reliquefaction resistance of Toyoura sand. A series of postliquefaction monotonic tests was conducted to investigate the degrees of induced fabric anisotropy at different states of liquefaction and subsequent reconsolidation. A series of reliquefaction tests was performed on sandy specimens that had experienced medium to large residual shear strains (γres) and that had reconsolidated in different states, under various cyclic stress ratios (CSRs). It was shown that reliquefaction resistance of Toyoura sand is influenced highly by the residual shear strain during liquefaction and fabric anisotropy after reconsolidation. The experimental results were used to predict excess pore-water pressure (EPWP) buildup during liquefaction and reliquefaction as a function of shear strain or dissipated energy. The liquefaction/reliquefaction resistance of Toyoura sand was quantified using an energy-based criterion considering the integrated effects of strain history and soil fabric.