Residual Strength of Liquefied Sand Measured in a Ring Shear Device

Abstract

Abstract Earthquake-induced liquefaction flow slides have resulted in loss of life and major damage at many sites around the world. In order to better understand the mechanics of such slides, it is necessary to quantify the residual shearing strength of the liquefied soil. Small-scale stress-controlled experiments suggest that this residual strength is not a constant, but that liquefied sand can be modeled as a highly viscous stress-thinning fluid, whose resistance varies with the velocity of flow. We present results obtained with a ring shear device designed specifically to measure the large-displacement post-liquefaction residual strength of sands under strain-controlled conditions. Residual strength of a fine uniform sand was measured for a range of relative densities (Dr) from 19 % to 36 % at four different shear-strain rates, varying from 11 to 44 s−1 representative of flow slide velocities. Measurements show that the strain-rate-dependent Herschel–Bulkley model for stress-thinning fluids applies to the liquefied sand, with resistance increasing as strain rate increases, but suggest that at relative densities higher than perhaps 50 %, relative density dominates, and residual strength can be approximated as a constant.