Theoretical and numerical investigations of the effects of pore fluid on the dynamic behavior of saturated soils

The primary objective of the research was to investigate the effects of pore fluid on the dynamic behavior of fully saturated soils. Saturated soil is modeled as a two-phase system consisting of a solid phase and a fluid phase that are coupled through mechanical, inertial, and viscous effects. Compared to a single-phase analysis, the effects of pore fluid on the dynamic response of a two-phase saturated soil are primarily manifested in terms of effective density and hydraulic damping.; Effective soil density is related to the fraction of pore water that moves with the solid skeleton during shear wave propagation. Hydraulic damping is related to the energy dissipation caused by viscous forces and relative motions between solid and fluid phases. Theoretical investigations based on Blot theory indicate that, for small strains, the ratio of effective soil density to saturated soil density (always ≤1) and the hydraulic damping ratio are functions of specific gravity of solids, porosity, hydraulic conductivity, and wave frequency. The consideration of effective soil density and hydraulic damping may be important for high hydraulic conductivity materials (sands and gravels). If saturated soil density is used in such cases, calculated values of shear wave velocity will be underestimated and calculated values of shear modulus will be overestimated. Under rotational (shear) excitations, hydraulic damping in sands and gravels may have an important contribution to total soil damping, especially at small shear strain levels when the skeleton damping is small. Under compression wave excitations, hydraulic damping is influenced by the degree of saturation and boundary drainage conditions.; Numerical investigations were also conducted on the effects of compressible pore fluid on large strain consolidation and of finite media strain on shock wave propagation. Results show that increasing fluid compressibility has the effect of accelerating the consolidation process at early times and slightly delaying consolidation at later times. Results also demonstrate that finite strain-induced geometrical nonlinearities may have important effects on shock wave propagation with regard to particle velocity and wave speed and, therefore, should not be neglected.