Liquefaction Assessment in Unsaturated Soils

Liquefaction in soils has predominantly been associated with saturated soils. Under seismic activity, unsaturated soils are may also be susceptible to liquefaction. The implications of neglecting unsaturated soils that are close to saturation as the foremost rule for assessment of liquefaction can be risky and catastrophic. Hence, in this study, a cyclic double-walled triaxial device capable of applying suction via axis-translation technique was modified to conduct cyclic triaxial tests on suction-equilibrated specimens at a low suction state. In unsaturated soils, the presence of highly compressible air within the soil specimens may prevent the effective confining pressure from reaching zero, which is typically considered as initiation of liquefaction. Therefore, in this study, liquefaction was considered to occur when 5% double-amplitude strain was attained in the soil specimen. A series of suction-equilibrated cyclic triaxial test results on unsaturated soils were analyzed to study and verify the possibility of liquefaction in unsaturated soils. Additional suction-controlled monotonic triaxial tests were performed to compare the stress paths of the cyclic triaxial tests with their respective critical state lines to indirectly assess the hypothesis of liquefaction mitigation using an induced partial-saturation technique. It was observed that liquefaction was possible and detected in unsaturated cohesionless soils having relative density of 50% and a degree of saturation of above 70%. However, with desaturation the resistance to liquefaction in soils increased exponentially. This demonstrated the potential for induced partial saturation to mitigate liquefaction in moderately compacted soils whose degree of saturation is reduced to less than 70%.