Investigating effects of wave incident angle and joint depth on ground surface motion considering multiple reflections via coupled discrete element and finite difference method

In this study, the effects of incident angle and joint depth on the ground surface motion induced by the shear wave propagation across the rock mass were numerically assessed. A three-dimensional coupled discrete element-finite difference model consisting of a 40-m deep rock mass with a single joint, was developed using 3DEC software. The continuously yielding joint model was adopted to replicate the nonlinear behaviour of the joint under the influence of the seismic wave. Moreover, the role of the multiple reflections occurring between the ground surface and the joint in the ground surface motion was determined via the comparison between the models with and without the presence of the free surface. The results of this parametric study showed that a larger incident angle could lead to the amplification of both the horizontal and vertical components of the peak particle velocity captured on the ground surface. In addition, it was found that the multiple reflections can significantly amplify the ground surface motion, particularly when the joint with the shallow depth was present. Hence, it is critical for practicing engineers to take into account the joint spatial properties such as the joint orientation and depth, in conjunction with the multiple reflections, when making the prediction of the ground surface motion.