Seismic Responses and Damage Mechanisms of Deep-Buried Underground Powerhouse in Layered Rock Mass

Layered rock mass generally has adverse effects on the seismic stability of deep-buried underground powerhouses. Aiming at the complexity of seismic wave field in deep-buried underground powerhouses, the obliquely input methods of P and SV waves considering the incident direction and multi-incident surfaces are constructed in this study, respectively. It can convert the seismic wave input problem into the problem of solving equivalent nodal force acting on the artificial boundaries. Based on the characteristics of dynamic interaction between interlayers in layered rock mass, an explicit dynamic contact force method considering the seismic deterioration effect and bond-slip characteristics of interface is also presented to simulate various contact states such as bond, separation, and sliding. The combined application of the above methods to analyze the seismic response of underground powerhouse at Azad Pattan hydropower station shows that they could accurately simulate the seismic damage evolution process of deep-buried underground powerhouses in layered rock mass. The numerical results indicate that the obliquely incident seismic waves contribute to a larger seismic reaction of underground powerhouses, which largely lies in the amplitudes of the displacement and stress fluctuations. After considering the dynamic contact, the obvious seismic deterioration effect and interlaminar dislocation displacement occur between soft and hard rock, and the sidewalls suffer more severe deterioration degree than the top arch. The seismic damage area of lining structure is mainly distributed in the place where the soft rock strata pass through and the upper structure with larger free surface. Additionally, two major damage modes of underground powerhouses in layered rock mass, namely, damage due to structural deformation and interlaminar dislocation, are derived from the numerical results and can be reasonably explained by the corresponding damage mechanisms.