| The mechanical behavior of saturated geomaterials is largely governed by the interaction of the solid skeleton with the fluids present in the pore structure. This interaction is particularly strong in quasi-static and dynamic problems and may lead to the catastrophic loss of strength known as liquefaction, which has been observed as a result of severe earthquake loading. Traditional geotechnical analyses, based on simplified effective stress theories, commonly fail to fully describe the behavior of saturated porous materials, making it necessary to use more robust formulations. In this context the use of multi-phase theories appears to be an alternative and more appropriate approach to account for a realistic behavior of saturated porous media. In this work the governing equations of a porous media interacting with immiscible porous fluids are derived in the light of the theory of mixtures. Appropriate constitutive relations for the solid and fluid phases are devised from laws of thermodynamics and the plasticity theory. A generalized Galerkin procedure is devised to establish the coupled mixed finite element equation set with a u-p-U form. An unconditionally stable implicit solution procedure is used for the time domain numerical solution. Numerical solutions corresponding to elastic saturated granular soil deposits under transient loads are compared with closed form solutions published in the literature. In addition, a numerical study of liquefaction is performed showing the capabilities of the proposed formulation and implementation to simulate the generation of pore water pressures and the loss of strength observed in loose granular soil deposits under seismic excitations. |
