Failure Modes of Air Desaturated Sand in Undrained Cyclic Loading: A Systematic Experimental Investigation

Abstract

This paper presents a systematic experimental investigation to understand different failure modes of air desaturated clean sand in undrained cyclic loading for a degree of saturation in the range of 70% to full saturation. Five distinct failure modes have been observed depending on the degree of saturation, relative density, effective confining pressure and cyclic shear stress ratio. Nearly saturated samples of loose sand at low confining pressure underwent hybrid cyclic liquefaction failure wherein it reached dense of critical state during compression stage of loading only. However, nearly saturated samples of medium dense sand at low confining pressure accumulated large plastic strain on the compression side owing to gradual strain softening. Both loose and medium dense samples, with a high degree of saturation, underwent cyclic mobility failure at high effective confining pressure, wherein the sample reached dense of critical state during both compression and extension stage of loading. Moreover, two types of cyclic softening failures, demarcated by two distinct phase transformation trends, were observed in samples with a low degree of saturation. Investigation from the critical state soil mechanics framework revealed that all test samples lay on the dense-of-critical side, and nearly saturated samples closest to critical state underwent cyclic mobility failure, whereas those at farthest from critical state failed by gradual strain softening.