A mechanical analysis model for tunnels under strike-slip faulting considering the fault zone width and nonlinear tunnel-stratum interaction

Abstract

Tunnels crossing active fault zones are seriously damaged under the action of faulting. However, the influence of the fault zone width or nonlinear tunnel-stratum interaction is neglected in existing analytical models, resulting in incorrect estimation of the tunnel mechanical response. To aid in the seismic design of tunnels, a mechanical analysis model for tunnels under strike-slip faulting considering the effect of fault zone width and nonlinear tunnel-stratum interaction is first proposed in this work. The calculation results of the proposed model agree well with those obtained from the model test and numerical simulation, and the accuracy is obviously higher than that of the existing analytical methods. Compared with the FEM numerical model, the average errors of the peak bending moment, shear force and axial force calculated by the proposed model are 6.37 %, 11.00 % and 9.91 %, respectively. Neglecting the effect of fault zone width or nonlinear tunnel-stratum interaction, the tunnel response will be misestimated, e.g., when the fault displacement is 3 m and the crossing angle β is 90°, the overestimated value is approximately 40–110 %. Finally, the results of parameter analysis show that under the condition of 0° < β < 90°, the tunnel failure scope caused by the left-lateral strike-slip faulting is obviously larger than that caused by the right-lateral strike-slip faulting, while the conclusion is opposite under 90° < β < 180°; the maximum strain within the tunnel correlates directly with fault displacement and the strength of the fault zone, exhibiting an inverse correlation with the width of the fault zone; meanwhile, the scope for tunnel failure is directly influenced by fault displacement, fault zone width, and the crossing angle (where 90° <β < 180°), while inversely affected by the crossing angle (where 0° <β < 90°) and the strength of the fault zone.