Inverse effect of packing density on shear wave velocity of binary mixed soils with varying size ratios

Abstract

This study evaluates the dependency of shear wave velocity (Vs) on packing density of binary mixed soils with varying size ratios of the small to large particles. 4 mixtures with different size ratios (sr = median grain size of small particles / median grain size of large particles) of 0.699, 0.282, 0.157, and 0.014 were prepared, bender element tests were then carried out to examine the variation of Vs according to the void ratio or relative density. The results demonstrate that when sr > 0.414 (the theoretical pore size ratio, which is the ratio between the diameter of interstitial sphere and the diameter of spherical particles, for simple cubic packing) and when sr < 0.155 (the theoretical pore size ratio for cubic tetrahedral packing), the measured Vs increases with increasing packing density due to the increase in interparticle coordination. However, when 0.155 < sr < 0.414 and the finer fraction < threshold finer fraction, the Vs of the tested mixture decreases with increasing packing density. This inverse impact of packing density on Vs may be attributed to the decrease in pore size between large particles in this situation and the consequent active disruption of direct contacts between large particles.