Damage Evaluation of Circular Tunnels Subjected to Local Deformation in Fault Crush Zones

Tunnels that cross fault crush zones are subject to local deformation along these zones during earthquakes. Because the tunnel axis and the fault plane generally intersect in a three-dimensional manner, evaluating structural performance by using three-dimensional FEM is reasonable, and to this end selection of an appropriate damage indicator is required. To establish a damage evaluation method for the safety of tunnels subjected to local deformation, three-dimensional FEM analysis was carried out on previous loading experiments, the failure modes were analyzed, and the applicability of several damage evaluation indicators was verified. As a result, the damage to the tunnel in the model experiments was broadly classified into in-plane shear in the longitudinal section and out-of-plane shear in the longitudinal or transverse section. Performance evaluation using compressive damage indicators including minimum principal strain when the limit state of a tunnel is defined as the point at which the resistance to slippage in the crush zone is maximum was found to be feasible. Moreover, the results of the sensitivity analysis showed that evaluation based on the minimum principal strain is broadly applicable. Additionally, a limit value considering element size was proposed.