Liquefaction Resistance and Cyclic Response of Air Injected Desaturated Clean Sandy Soil Experimental and Numerical Investigations

Abstract

Liquefaction has been one of the major concerns in the field of geotechnical earthquake engineering. Various mitigation techniques such as vibroflotation, deep dynamic compaction, explosive compaction, grouting, deep soil mixing etc. have been employed over the last fifty years. These techniques either densify the in-situ soil or fill the voids with some external agent. Some of these techniques are costly, while others pose a threat to the adjacent structures and environment. Over the last couple of years, induced desaturation is emerging as a possible cost-effective and environment-friendly liquefaction mitigation technique. In this technique, the degree of saturation of the in situ saturated soil is reduced either by injecting air or by generating some kind of gas within the soil matrix. The present study investigates the liquefaction resistance and cyclic response of the air-injected desaturated clean sandy soil. The large number of stress controlled undrained cyclic triaxial tests were conducted on samples with the degree of saturation in the range of 70 % to 99 %. Three relative densities of 30 %, 40 % and 60 % and initial effective confining pressure of 25 kPa, 50 kPa and 100 kPa were considered for the investigation. Cyclic shear stress ratio (CSR) was 0.175, 0.250, 0.300 and 0.400. It was found that the number of cycles required for initial liquefaction increased exponentially with the reduction in the degree of saturation. Cyclic strength of desaturated sand with relative density of 40 % with the degree of saturation of 80 % was found to be almost twice that of fully saturated sand. Depending upon the degree of saturation, relative density, confining pressure and CSR, five distinct failure modes were observed: 1) Hybrid cyclic liquefaction 2) Cyclic mobility-gradual/catastrophic 3) Cyclic softening-CE 4) Cyclic softening-E and 5) FAPSC-SS: Failure due to Accumulation of Plastic Strain on the Compression side as a result of gradual Strain Softening. Samples with a high degree of saturation underwent...