Effect of initial gross void ratio on undrained cyclic pore pressure response of sand-silt mixtures

Abstract

The rate and magnitude of excess pore water pressure generated during seismic loading considerably influences the shear strength, shear stiffness, deformation and settlement characteristics of soil deposits, thereby affecting the stability of structures constructed from or founded on it. Sometimes the soil may liquefy resulting in a complete loss of strength. A review of related literature on the pore pressure generation characteristics and in turn the cyclic resistance behavior of sandy soils appears to be confusing. In order to clarify and assess the pore pressure generation characteristics of sandy soils, a series of undrained stress controlled cyclic triaxial tests were conducted on various sand and silt mixture specimens of 50mm diameter and 100mm height at various constant gross void ratios. The gross void ratio of a specimen is determined by the ratio of volume of voids to the volume of solids. The results obtained from this study indicate that the limiting silt content and the relative density of a specimen irrespective of its silt content play the major role in the generation of excess pore water pressure in sandy soils. The rate of generation of excess pore water pressure was found to be the maximum at the limiting silt content. Higher generation in excess pore water pressure was observed in specimens at silt contents below the limiting silt content than their counter parts at silt contents beyond the limiting silt content. The generation in excess pore water pressure was seen to be a strain dependent one and this has been analyzed with respect to the shear strains generated during each cycle of loading. At given silt content, the rate of generation of excess pore water pressure was seen to increase with increase in void ratio of the sand-silt mixture.