# Seismic Response Analyses of a Large-Span Powerhouse Cavern Considering Rock-Structure Interaction
## 1 Introduction  
Stability analysis of large-span underground caverns at the design stage, during construction, and in service is a very challenging work in underground excavation engineering. Historically, underground facilities have experienced a lower rate of seismically induced damage than surface structures. Nevertheless, some underground structures have experienced significant damage in recent large earthquakes, including the 1976 Tangshan, China earthquake; the 1995 Kobe, Japan earthquake; the 1999 Chi-Chi, Taiwan, China earthquake; the 1999 Kocaeli, Turkey earthquake; the 2004 Niigata, Japan earthquake; and the 2008 Wenchuan, China earthquake, and some more recent earthquakes such as the 2016 Kumamoto, Japan earthquake, and the 2016 Norcia, Italy earthquake [1, 2, 3, 4, 5, 6, 7, 8]. In particular, the Daikai subway station collapse, the first collapse of an urban underground structure due to earthquake forces rather than ground instability [1], significantly changed the public belief that underground structures had the ability to sustain earthquakes with little damage. Underground structures, varying widely in shape and size, refer to many lifeline facilities such as pipelines for water, sewage, gas, electricity and telecommunication, subways, roads, storage tanks, parking lots, and common utility tunnels. While earthquakes, as some of the most devastating natural disasters, may lead to damage to crucial underground structures such as those associated with the electrical transmission and distribution, water supply, transportation and communication, and even disaster prevention and rescue systems, resulting in catastrophic disasters.  
According to the available data, the seismic damage of underground structures includes three main categories, i.e., damage from ground shaking, damage from fault displacement, and damage from ground failure. The major factors for shaking-caused damageare: (1) the shape, dimensions, and depth of the structure; (2) the properties of the surrounding soil or rock; (3) the material properties of the structure; and (4) the severity of the ground shaking [9; 10; 11]. Nowadays, with the increasing number of underground structures with large cross-sections compared with less information on their seismic behaviors, it is imperative to carry out relevant seismic analysis. Analytical methods are usually limited to simple computational models and ideal seismic inputs [12]. Modern performance-based design methods require detailed seismic response analysis of the rock-structure system to investigate the seismic performance and fragility of underground structures under earthquake events [13; 14; 15; 16; 17]. More efficient numerical methods should be developed for practical complex models, especially three-dimensional models capable of accurately simulating the seismic response due to the additional seismic loadings, which induce stress redistribution and three-dimensional deformation.  
In this paper, following geological and geomechanical investigations with laboratory and in situ testing, a complete sophisticated numerical model is constructed for the seismic response analyses of a large-span powerhouse cavern considering rock-structure interaction. The seismic input is selected from the past earthquake records, corresponding to the seismic characteristics of the site. Although the site is not located in a high-magnitude seismogenic zone, the dynamic modeling studies are of significance to underline the approach adopted.