Steady-state concepts and static liquefaction of silty sands

The results from an experimental study on silty sands are presented and evaluated in view of the framework of critical-state or steady-state soil mechanics. Drained and undrained compression tests were performed on Nevada sand containing nonplastic silt. The drained and undrained steady-state lines diverged. This divergence was caused by the tendency for static liquefaction at low pressures. Results from undrained tests with different initial void ratios produced different steady-state lines. Unique steady-state lines may therefore not always exist for silty sands. Denser specimens liquefied at low confining pressures, while looser specimens at higher confining pressures showed stable behavior. Thus, a unique relation between void ratio and confining pressure, namely the steady-state line, may not represent the behavior of loose silty sands. This occurs because silty sands exhibit "reverse" behavior characteristics; more dilative behavior is observed with increasing confining pressure under undrained shearing. Load and deformation control testing was performed to evaluate the effect of strain rate. Compressibility was examined as an alternative measure of liquefaction potential.