Effect of Gradation and Non-plastic Fines on Monotonic and Cyclic Simple Shear Strength of Silica Sand

Monotonic and cyclic direct simple shear tests with shear wave velocity measurements were conducted on a series of silica sand gradations to examine the effect of both fines content and grain size distribution. Two test series were considered, one with parallel gradations with decreasing D₅₀ and constant C_c, C_u values (N-series), and a second one where C_c was kept constant and C_u, D₅₀ values varied (W-series). In both series, the fines content varied from 0 to 50%. The most dramatic effects were noted for the clean sands as the C_u value increased and for the silty sands as fines content increased from 1 to 50%. In general, static and dynamic behavior was observed to depend on the amount of fines, C_u and D₅₀ values. The same was true for pre-cycling and post liquefaction shear wave velocities. Post-liquefaction shear wave velocities were on the order of 8–13% of the pre-cycling values.