Numerical simulation of seismic response of a deeply-buried underground cavern in interbedded rock mass

In order to study the seismic wave field characteristics of large deeply-buried underground caverns, the input methods for obliquely incident earthquakes in deeply-buried underground caverns are proposed by converting the site seismic response into the equivalent load acting on the artificial boundaries. It is suitable to reflect the incident direction, the multi-incident surfaces and the inconsistency of near-field obliquely incident earthquakes. According to the dynamic interaction characteristics between interlayers in interbedded rock mass under seismic action, a dynamic contact analysis method considering the seismic deterioration effect and the bond-slip characteristics of interface is also established. Consequently, a dynamic response analysis method for a deeply-buried underground cavern in interbedded rock mass under obliquely incident seismic waves is constructed and applied to the seismic damage evolution process analysis of the underground powerhouse of Azad Pattan Hydropower Station. The simulated results reveal that the obliquely incident earthquake aggravates the seismic reaction of lining structure, which mainly lies in the amplitudes of the displacement and stress fluctuations. Some areas at the upper side wall and the arch of the linings in the main powerhouse are damaged to the most severe degree. After considering the dynamic contact, the seismic response of caverns near interface further increases, and the evident seismic deterioration effect and shear slip failure occur at interface. The dislocation between interlayers is more obvious, and the maximum dislocation displacement tends to be stable at 5.9 cm. Besides, the seismic damage characteristics and failure modes of the lining structures of the underground powerhouse in interbedded rock mass are discussed from the transverse and longitudinal angles.