Abstract: In previous studies on the mechanisms of deformation and failure of tunnels across active faults, the two effects of quasi-static faulting and seismic excitation were often studied separately, ignoring the possibility that the two effects are often threatening to the tunnel at the same time in the high seismic risk zone. In this study, sophisticated numerical methods and constitutive models were used to study the effect of combined fault rupture deformation and subsequent seismic excitation upon a tunnel. The weakening of the rock-tunnel interface under relative dislocation and degradation of the concrete material in the tunnel liner were considered. The deformation response and failure mechanism of the tunnel subjected to combined fault rupture deformation and subsequent seismic excitation were investigated. Relative deformation time histories, plastic strain, tensile strain of the tunnel were studied. And the performance of “joint” design was numerically verified, followed by a detailed parameter study that aimed to provide deep insight into the design factors of the technique of “flexible jointing”. The influences of some important factors were investigated, such as the range of the joints, length of the segments, and infill material properties. The results indicated that: (1) When solely affected by the faulting, the influence and damage to the tunnel are limited within the fault zone, while the other parts of the tunnel remain relatively intact. (2) Under the combined fault rupture deformation and subsequent seismic excitation, notable ovaling deformation and roof settlement would occur in the tunnel liner, also the tunnel spring line would suffer significate damage. Tunnels with initial faulting induced damage would suffer more damage under the action of earthquakes, and the damage degree increases with the increasing initial faulting distance. (3) The flexible joint design could decrease the tunnel’s relative deformation under the combined effect and enhance the stability of the tunnel. However, it should be noted that this benefit would be limited within the fortification range. (4) The suggested range of the fortification would be slightly larger than the width of the fault. A smaller segment length is preferred to improve the tunnel’s stability. And it seems that the width of the joint is irrelevant with the performance of the tunnel under the combined effect. As a preliminary exploration, current research results provide a certain reference for further improving the seismic resistance and fault resistance of underground engineering in strong earthquake areas in western China.

Key words: tunnel, quasi-static faulting, strong earthquake, rock-concrete interaction, joint design