Recently, analyzing the effects of fault displacements on a fault-crossing tunnel has been in focus, in regard to vulnerability assessment, as well as the design of safe underground structures. The current study involves a large-scale seismic rupture simulation of an entire fault, tunnel and the surrounding crustal rock area. The parallel finite element program FrontISTR, was modified to include RC nonlinearity and fault modelling in the current study. The model was prepared using solid elements for the crust and joint elements for the fault surface. The tunnel is modelled using non-linear concrete solid elements and anisotropic plane-stress reinforcement steel elements. Through numerical simulation, the influence of considering dynamic fault rupture and tunnel non-linearity are investigated. This study highlights the importance of considering dynamic fault rupture with respect to the damages incurred by the tunnel, realized through its displacement mode, material degradation and crack patterns.
In recent years, the evaluation of fault displacement is required for evaluating the soundness of underground structures during an earthquake. Fault displacements occurs as the result of the rupture of the earthquake source fault. Previous studies have been primarily conducted using the finite difference method (Dan et. al 2007), where the dynamic rupture simulation is performed through the spontaneous rupture process of a fault caused by a slip-weakening model. Few studies have also been done using the finite element method (Mizumoto et al. 2005), but the large computation requirement involved restricted the complexity of the model.
The present study used the 3D nonlinear finite element method to perform the simulation of the Kamishiro Fault earthquake in Nagano Prefecture on November 22, 2014(JAEE 2015). A 40 km × 40 km × 20 km model that included the earthquake source fault is modelled using solid elements for the crust and joint elements for the fault (Mitsuhashi 2017). A 100m tunnel crosses through the fault.
The rupture in the model is generated by applying an initial stress to the joint elements, which initiates the rupture process, as it uses a nonlinear constitutive law with a stress drop beyond failure. The simulation is performed through the FrontISTR, a massively parallel finite element program, which can perform large-scaled FEA with relative ease (Front ISTR 2018).