The steeply dipped fault zone is the weak link of the seismic stability of underground caverns. Aimed at the complex dynamic interaction characteristics between surrounding rock and faults

based on the Ladanyi’ shear strength model

a seismic deterioration coefficient was introduced

and a shear strength model considering nonlinear mechanical properties and seismic deterioration effect was established. Given the discontinuous deformation characteristics between surrounding rock and faults

a three-dimensional dynamic contact force method was proposed

which considered both the complex shear strength and multiple contact states. The method was applied to Jinchuan underground powerhouse to study its seismic damage characteristics under the influence of the steeply dipped fault F31. The results indicate that after considering the interfaces and seismic deterioration effect

the seismic response of the cavern increases

the dislocation between the surrounding rock and faults is more evident

and a certain depth of separation and sliding failure zones occurs. The steeply dipped fault cuts the high sidewalls of the main powerhouse

and forms a weak zone where the surrounding rock thinness is thin

resulting in larger deformation and damage. The flexural toppling deformation and slipping deformation into the cavern tend to occur on the upstream and downstream sidewalls

respectively. The distribution of the sliding and separation failure zone of the interfaces between surrounding rock and faults changes dynamically with the seismic process and extends to the depth. Among them

the separation zone is relatively large at the arch abutment and rock anchoring beam. The numerical results reveal the dynamic failure mechanism of surrounding rock of underground cavern intersected by a steeply dipped fault

which can provide reference for seismic design.