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 D-50 and constant C-c, C-u values (N-series), and a second one where C-c was kept constant and C-u, D-50 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 D-50 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.