Abstract
The tunnel industry has considered that tunnels, especially tunnels in rock, are naturally resistant to earthquake action, including faulting, shaking, deflection and ground failure. As the number of case histories of tunnels subject to earthquake action has increased, the industry has started to recognize that, although tunnels in rock have good resistance against earthquakes generating peak ground accelerations (PGA) lower than 0.5 g, it is important to include the dynamic forces and displacements generated by seismic ground motions in the design process to obtain a more reliable design. These additional earthquake forces impact the final design, potentially requiring changes to the ground support and additional reinforcement of the concrete lining, as illustrated by case histories presented in this paper.
Introduction
The tunnel industry considered that tunnels were naturally resistant to earthquake action for many years, as they did not experience the same high levels of shaking as surface structures. This perception was supported by the relative good historic performance of tunnels and underground structures, especially of tunnels in rock, during large earthquakes. Dowding and Rozen (1978) presented one of the first compilations of damage to rock tunnels due to earthquake shaking. They collected information on 71 tunnels and compared their behavior with estimated peak ground accelerations (PGAs) and peak ground velocities (PGVs).
Conclusions
This brief review of literature and review of specific case histories the author has been involved in indicate that tunnels in rock generally are capable of withstanding moderate earthquake events without the need to modify their designs. However, to increase the reliability of the tunnel structure and to accommodate larger events at closer distances, it is necessary to consider the effect of the dynamic loads generated by earthquakes.
