Abstract: There is a complex geological structure and well-developed seismic activity in at the underground powerhouse of SK Hydropower Station site in Pakistan, so it is urgent to study the seismic response of the underground structure. The three-dimensional numerical model was established by using the finite element software ABAQUS. The acceleration, velocity and stress response characteristics of the underground powerhouse were analyzed by using the dynamic time-history analysis method, and its seismic stability was also studied. The results show that: (1) There is an obvious seismic amplification effect on the free face of the underground powerhouse. The worse the quality of surrounding rock, the more obvious the amplification effect. (2) During the earthquake, the stress state of the underground powerhouse is mainly affected by the original stress field formed after excavation. (3) The underground powerhouse is basically in a stable state under the earthquake with an exceedance probability of 50% in 100 years; the stability of underground powerhouse may not meet the requirement under the earthquake with an exceedance probability of 3.3% in 100 years. The study results can provide a reference for the actual engineering and similar engineering.

Key words: Underground Powerhouse, Earthquake, Dynamic Time-History Analysis Method, Dynamic Response, Stability