The incompatible deformation mechanism of underground tunnels crossing fault conditions in the southwest edge strong seismic zone of the Qinghai-Tibet Plateau: A study of shaking table test

Abstract

The study of the seismic damage mechanism of tunnels subjected to strong earthquakes is challenging frontier subjects. In strong earthquake areas, the survey and line selection design of tunnels and underground engineering avoid the identification of dense fault areas and large major fault fracture zones, but the active fault fracture zone, which is widely distributed, large depth and difficult to detect in location, is still at a loss. Due to seismic loadings, the dynamic response and failure mechanism of the surrounding rock are always unclear. This study involved on-site investigations and indoor shaking table tests to demonstrate how seismic activity affects the hanging wall, footwall, and fault during vibration processes as part of the Xianglushan tunnel major project. Additionally, we explored how these elements interact with each other despite their incompatible deformation laws. The incompatible deformation effect of the dynamic tensile-compressive deformation effort and dynamic shear deformation effort were proposed. The quantitative description of dynamic uncoordinated deformation was given based on the wave function. In addition, the mechanism of dynamic deformation failure of the surrounding rock of tunnel was revealed by comparing the test results to the engineering site's deformation failure pattern. Experimental results show that the acceleration peak, strain peak and displacement time curve had obvious amplified effects in the horizontal and vertical directions, and the Fourier amplitude was shown as a consistent rule of change by the shaking table tests. The hanging wall and lower disks of the fault have obvious incompatible and inconsistent deformation effects, the vertical vibratory direction is represented by dynamic tensile-compressive deformation, and the horizontal vibratory direction is represented by dynamic shear deformation. The incompatible deformation theory and the wave function were introduced to reveal the dynamic failure mechanism of the surrounding rock across a fault combined with the deformation failure of the seismic tunnel site and shaking table test. The dynamic incompatible deformation caused by internal defects was accelerated by strong seismic activity. The dynamic destruction process of the surrounding rock of tunnel was the gradual failure process caused by stress damage accumulated in the rock surrounding the tunnel. The results can provide reference and data support for the safe construction of tunnels under complex geological conditions of dense faults in strong earthquake areas.