Seismic damage assessment and mechanism analysis of underground powerhouse of the Yingxiuwan Hydropower Station under the Wenchuan earthquake

The Yingxiuwan underground powerhouse is one of the closest large-scale underground structures from the epicenter of the Wenchuan earthquake and suffered significant damage during this earthquake. What makes this case even more interesting is that the seismic damage is mainly distributed in the upper part of the concrete structure in the underground powerhouse. A full three-dimensional dynamic finite element model of the underground structure and rock system is adopted to make a reasonable assessment for the seismic damage observed in the field and to study the damage characteristics and mechanisms of the underground powerhouse. Additionally, to approximate actual field conditions, the oblique incidence of seismic waves and the rock-structure interaction (RSI) are both considered in this study, and their effects on the seismic response are evaluated. The numerical results indicate that the oblique incidence of the seismic wave and the RSI both contribute to a larger seismic response, and the results compare well with the field observations when the two are considered. The damage distribution of the concrete structure is mainly dominated by the structure feature itself. The main cause of the severe damage in the upper structure is due to the lack of sufficient constraints on it, which leads to a large deformation in the upper structure.