Effect of Gradation and Stress Ratio on Liquefaction Response of Ennore Sand

Liquefaction behavior of soil is governed by several factors such as grain size, fines content, relative density, the magnitude of shear stress or strain, and loading conditions. Cyclic stress ratio (CSR) is one of the most important parameters that govern the liquefaction potential of sands during seismic events. The present experimental study investigates the effect of cyclic stress ratio on the liquefaction response of cohesionless soil. Five different types of specimens (S<inf>1</inf>–S<inf>5</inf>) were prepared including well-graded and poorly graded sands having definite proportions of three commercially available grades of Ennore sand. Grain size distribution (GSD) parameters such as coefficient of uniformity (C<inf>u</inf>) and co-efficient of curvature (C<inf>c</inf>) were also determined for all the five specimens. A series of stress-controlled cyclic simple shear tests were performed on these specimens prepared at 60% relative density over a wide range of CSR (0.1, 0.075, 0.05, and 0.03). The criteria for the liquefaction initiation in the present study was chosen as r<inf>u</inf> = 1.0; where r<inf>u</inf> = excess pore water pressure ratio. The number of cycles to liquefaction was observed to increase with the reduction in CSR value for all five specimens. Well-graded specimen (S<inf>4</inf>) exhibited more resistance toward liquefaction than uniformly graded specimens (S<inf>1</inf>, S<inf>2</inf>, S<inf>3</inf>, and S<inf>5</inf>) at same CSR values. The shear modulus (G) of all the specimens was observed to decrease with the reduction in mean particle diameter (D<inf>50</inf>) for all CSR values.