Experiments and modelling of silty sands susceptible to static liquefaction

Most historic cases of liquefaction have been found to occur in alluvial (w ater) deposited silty sands. Currently, the effect of non-plastic fines (pa rticles smaller than No. 200 sieve) on the liquefaction behaviour of sands is viewed to be either negligible or its presence actually inhibits liquefa ction. Undrained triaxial compression test results performed on silty sands clearly indicate a direct correlation between the quantity of finer, non-p lastic constituents and the liquefaction potential of granular soils. Incre asing the fines content increases the liquefaction potential, even though t he density increases, Complete static liquefaction occurs at low confining pressures. As confining pressures increase, the liquefaction potential decr eases resulting in increased stability. Thus, silty sands exhibit a 'revers e' pattern of soil behaviour with confining pressure. Drained tests indicat e both a large contractive volume change and a suppressed friction angle at low confining pressures, and this explains the undrained behaviour, It is hypothesized that the mechanism underlying this behaviour is related to the formation of a particle structure between the large and small grains which creates a highly compressible soil fabric. This 'reverse' behaviour patter n makes predictions of static liquefaction of silty sands difficult. Howeve r, simple modifications to the Single Hardening Model yield surface formula tion enables predictions of this behaviour pattern. Copyright (C) 1999 John Wiley & Sons, Ltd.