Abstract: The earthquake induced permanent deformation is a key index for aseismic safety evaluation of rockfill dam. In order to calculate the permanent deformation reasonably, both residual volumetric strain and residual shear strain induced by the earthquake loading should be taken into account. For this reason, the method presented by LIU Han-long is modified. In the modified method, the residual volumetric strain is modeled by a shear-dilation-based approach. The derivation of the dilatancy modulus matrix is given in detail; and the calculation parameters and the analysis steps are also introduced. To test the reliability of dilatancy modulus matrix, the permanent deformation mode of a typical element is analyzed, the computed shear strain and volumetric strain are in good coincidence with the theoretical values. After that, the proposed method is used to calculate the earthquake induced permanent deformation of a core rockfill dam and a concrete faced rockfill dam. The computed distributions of the vertical, longitudinal and transversal permanent displacements are studied in detail. By comparing with the measured results, it is found that the dam deformations are mainly residual settlement; and the horizontal displacements are relatively small. It is proved that the proposed method can catch the features of the permanent deformation behavior of rockfill dam and it can give more reasonable results.

Key words: earthquake induced permanent deformation, residual volumetric strain, residual shear strain, shear contraction, finite elements