Seismic damage mechanism of tunnels through fault zones

First of all, a simple investigation into the responses of tunnels through fault zones during Wenchuan Earthquake and other major earthquakes is made. Then comparative analyses are carried out by means of shaking table model tests and numerical analyses, mainly on acceleration characteristics of the surrounding rock and tunnel structures, deformation laws of geological strata and distribution of internal forces and so on. The analyses indicate that the results of investigations, tests and numerical analyses are in good agreement and that the tunnels through fault zones are easily damaged. The acceleration response in fault contact segments is discontinuous, and the peak acceleration is obviously larger at the fault zones at the same elevation. The tunnel structure has little impact on the response of geological strata during earthquakes, and the behavior of the tunnel structure obviously adheres to and relies on geological strata in the fault zones. The tunnel dislocation damage mechanism is the relative displacement between the fault zone and the surrounding rock, and the relative displacement value is relative to the types of the surrounding rock. The tunnel cross-sectional structure in the fault zones has the same distribution characteristics of internal forces, that is, in conjugate directions of 45°, it is the greatest, but the tunnel structure has relatively higher internal forces and is easily damaged during earthquakes. Those findings are of great importance to the rational understanding of earthquake response behaviors of tunnels through fault zones, and they may provide precious data for the earthquake resistant design and construction of practical projects.