Liquefaction Potential Assessment of Brahmaputra Sand Based on Regular and Irregular Excitations Using Stress-Controlled Cyclic Triaxial Test

The response of saturated soil during earthquakes is governed by many factors such as frequency content, strain, stress, excess pore-water pressure and strength variations within the soil mass. This paper highlights the effect of strains on the stiffness modulus and its degradation at the liquefied condition of cohesionless soil. Cyclic triaxial (CT) tests, in stress-controlled manner, were carried out on saturated sandy soil specimens made at different relative density (Dr = 30%–90%) and effective stress (σ′c = 50–200 kPa). The reconstituted specimens were subjected to regular and irregular stress histories. Representative strong motions with varying PGA were chosen, and the corresponding irregular stress histories were used. Additionally, regular stress histories constituted from different cyclic stress amplitudes were also used. The responses of the saturated specimen were obtained in terms of the excess pore-water pressure generation and strain accumulation with elapsed time. In comparison to the standard frequency and duration parameters (namely the predominant period and significant durations), it is observed that the responses are more influenced by Arias intensity and specific energy density of the strong motion. Based on the increase in pore-water pressure, reduction in shear modulus and increase in shear strain within the specimens, the complete manifestation of liquefaction is divided in four zones, namely the no liquefaction zone, quasi-liquefaction zone, zone marking the onset of liquefaction and the completely liquefied zone. The criteria for the onset of liquefaction of Brahmaputra sand involving shear strain, peak ground acceleration and cyclic stress ratio are provided.