Fortified length of the tunnel under the S-type fault displacement pattern

Abstract

Many tunnels have been built in central and western China; these tunnels are facing serious damages of active faults. At present, the fortified length of tunnels remains to be solved under fault dislocation. To overcome this issue, a numerical calculation model is established on the basis of previous research on the numerical calculation and model test of tunnels across active faults, with Xiang Lushan tunnel project as the research background of the paper. The S-type fault displacement pattern is proposed, which is based on the deflection curve of the support of the fixed beam at both ends under the uneven settlement. The influence of S-type and linear fault displacement patterns on tunnel lining is investigated using the finite difference method. Meanwhile, through the orthogonal test of fault factors at different levels, the influence rule of the multi-factor combination of faults on the fortified length of the tunnel under the S-type fault displacement pattern is obtained. Results reveal that the S-type fault displacement pattern, compared with the linear displacement pattern, can eliminate the stress singularity at the boundary of the fault zone. Therefore, the S-type fault displacement pattern is more reasonable and can be used as the selection of fault displacement pattern. In addition, the fortified length of the tunnel ranges from 1.1 L to 2.0 L (L is the fault width), which is the result of the orthogonal test. The most influential factor for the fortified length of the tunnel is the angle between the fault strike and the tunnel axis, whereas the least influential factor is the fault dip angle. This research provides a reference for the fortified range of the tunnel crossing fault with certain practical significance.