Saturated Sand as an Inelastic Two-Phase Medium

The inelastic densification produced by shear straining saturated sands is opposed by the elasticity of the pore water and leads to a pore pressure increase, which causes a decrease in the intergranular frictional forces and consequent liquefaction of the sand mass. This inelastic densification is accompanied by an inelastic strain of the fluid phase, and the magnitude of the developed pore-water pressure is the product of the inelastic densification and the densification compliance, the latter of which is approximately equal to the drained compressibility of the sand. The tangent (incremental) elastic moduli are expressed in terms of the drained and undrained compressibilities of the two-phase medium and the compressibilities of water and the solid matter forming the grains. It is demonstrated that the volume change of the grains due to intergranular stresses has a negligible effect on the material parameters, even though it roughly equals the volume change of the grains due to the pore-water pressure, which has an appreciable effect.