Abstract: The depositional environment of the bedrock of Xiaonanhai Dam is dominated by floodplain sub-facies. The strata are mainly composed of siltstone and mudstone interbedded. Tectonic leads to the buckling of layers, and groundwater causes the softening and mudding of wear intercalation. Those are three essential factors for the formation of intercalated shear zone in the alternatively distributed soft and hard rock layers. The macro-properties of shear zone can be simulated in mesomechanical level by particle flow code (PFC). On the basis of particle flow theory, PFC^2D models of shear zone were established to study its shear failure process, in which different contact bond constitutive relations were introduced. The simulation test focused on the void ratio change, as well as the position, width, angle and spacing of the shear cracks. Results show that the shear failure process of the model is consistent with the development of slip surface in clay which was proposed by A.W. Skempton. Eight PFC^2D models of shear zone samples with different thicknesses and lengths were compared, and the simulation results reveal that when the thickness of hard and soft rock is fixed, the longer sample leads to the gentler angle of the cracks and larger spacing between them. Meanwhile, micro-cracks are prone to be concentrated initially in both ends of the shear zone. Maintaining the length and the thickness of hard rock, the spacing of the cracks becomes larger with the increasing thickness of shear zone, but the angle remains unchanged.

Key words: red bed, intercalated shear zone, particle flow code, mesomechanics, shear failure