Time-Frequency Analysis of Seismic Wave Propagation across a Rock Mass Using the Discontinuous Deformation Analysis Method

To investigate the wave (including P-wave and S-wave) propagation across a rock mass, the seismic discontinuous deformation analysis (DDA) method is used, and a time-frequency analysis of the DDA simulation results is performed in this paper. First, compared with the theoretical solution, the correctness of the DDA to simulate the seismic wave propagation across both the interlayer and interface is validated. Second, the propagation effects of the seismic wave across the jointed rock mass are studied, showing that the joint stiffness, joint spacing, and joint number have different effects on the attenuation of seismic waves. Last, to analyze seismic wave propagation across a rock mass, the engineering site of the underground cavern complex of the Dagangshan hydropower station in southwest China is used as a typical case study. A number of valuable results are obtained by time-frequency analysis; an obvious topographic amplification effect and a joint abnormal area are found. From the analysis of the time-space effect, it may be concluded that the relative displacement of the rock mass is easily encountered under earthquake, which adversely affects the stability of the engineering site. The spectrum characteristics of the seismic dynamic responses at different locations are significantly different, and a weak area of the peak acceleration may be caused by the joint attenuation effect. Based on the joint time-frequency analysis, it is suggested that adjustments for both the peak acceleration and spectrum be made before taking the ground motion record as the incident wave.