Pore pressure predictions in finite element analysis

Abstract Many of the existing pore pressure models for FEM analysis are limited either to cases where the pore pressure component produced by the shearing stress is neglected (usually restricted to static analysis) or where the component produced by the mean confining stress is disregarded (usually restricted to cyclic loading, as in earthquake and offshore engineering). A pore pressure model including the simultaneous effects of shear and mean confining stresses is presented in this paper. The model is simple and applicable to static as well as cyclic loading. The conceptual relationship between strains and pore pressure is well recognized in soil mechanics; however, it is difficult to determine the strains by FEM with the necessary accuracy to ensure satisfactory pore pressure predictions, mainly in the range of strains where the concepts of stress path are best applicable. To overcome this limitation, the proposed technique introduces a pore pressure function, to be coupled to a potential and a loading function in an elastic—plastic constitutive model. For simplicity, it is assumed that the pore pressure response can be satisfactorily represented by a path dependent calibrating function determined to fit experiments over a given range of confining pressures. This procedure allows the independent determination of the pore pressure increment before the iterative elastic—plastic procedure is activated, thus supplying the constitutive model directly with the appropriate direction and magnitude of the effective stress increment. The advantages of this procedure during undrained loading are presented in the text.