On Limitations of a Coupled Dynamic Analysis of Saturated Porous Media

The main objective of this paper is to point out limitations of a coupled finite element analysis involving saturated soils subjected to fluctuating load. For this purpose an experimental program has been carried out in which a sample of medium dense sand was subjected to a cyclic loading history under free-draining conditions. The results showed that, in spite of the high permeability of the material, the consolidation settlements were insignificant. The mechanical response of this sample was then simulated using coupled finite element analysis based on Biot’s formulation. The analysis predicted high settlement amplitudes, which were inconsistent with the experimental data. This indicates that the applicability of Darcy’s law, which governs the transient flow, is restricted to the case when the hydraulic heads undergo a slow monotonic change, whereas under a typical scenario involving fluctuating load (e.g. an earthquake excitation) the conditions remain essentially undrained.