Impact of seismic design on tunnels in rock - Case histories

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.