Rock Tunnel Behaviour Under Seismic Loading

Predicting the behaviour of tunnels and tunnel supports under dynamic or seismic loads, especially in jointed rocks, is a major challenge. Though tunnels are mostly considered relatively safe under earthquakes, worldwide many failures are reported. In this paper, tunnel behaviour under earthquake loading is briefly discussed. When the surrounding rock is jointed, tunnel and tunnel support response become quite complex, and under dynamic loads, complexity increases many folds. Tunnel behaviour under an earthquake is influenced by many different parameters like peak ground acceleration (PGA), frequency content, magnitude and duration of earthquake, tunnel depth and confinement, rock joint properties, support system, etc. Some of the influencing parameters are studied using UDEC, and corresponding results are discussed here. The analysis carried out on one of the headrace tunnels of a famous hydroelectric project under different seismic loads is highlighted, and some of the salient results are presented and discussed.