Cyclic Behaviour of Sand Under Bidirectional Shear Stress With Various Phase and Frequency Differences

ABSTRACT The horizontal cyclic load on sand foundation is often coupled in multiple directions, and the load in other directions will significantly affect the dynamic characteristics of soil. To systematically study the cyclic behaviour of sand under multi‐directional dynamic load coupling, the cyclic shear tests under three shear paths with four different stress amplitudes were carried out on sand. The strain development, vertical stress evolution and strength characteristics of the sample were studied and the effect of shear path and stress amplitude on them was analysed. The test results show that the development of vertical stress with the number of cycles is basically the same under different shear paths and stress amplitudes. The damage resistance of sand under different shear paths from high to low is linear, circular and figure ‘8’ shear path. It indicates that for the bidirectional shear test, the X direction strain of the sample is affected by the Y direction stress. In addition, a modified expression of cyclic shear ratio (CSR) under bidirectional shear path was proposed. Based on the modified CSR, a unified expression of the number of cyclic failures for sand under linear, circular and figure ‘8’ shear paths was established. It can accurately predict the number of cyclic failures for sand under complex shear paths by simple linear shear path.