Comprehensive identification and assessment of clastic rock and water-bearing breccia for water and mud inrush in tunnel: A case study

Clastic rock and breccia are mostly developed in fault fracture zones. Due to their poor stability and easy occurrence of water structures, tunnels are prone to collapse, water inrush and other disasters when encountering clastic rock and breccia, which seriously affects the safety of tunnel construction. In order to reduce the impact of such disasters on construction, the paper takes the No.4 branch tunnel of Xianglu Mountain in Yunnan as an example, and proposes a seismic ahead prospecting method- tunnel resistivity ahead prospecting method- advanced drilling method- cross-hole resistivity tomography method identification system for clastic rock and water-bearing breccia. The identification system integrates drilling methods and geophysical methods to obtain wave velocity information, reflection information, resistivity information and lithology information in the study area. The obtained information is used to jointly interpret the overall lithology fragmentation degree, lithology interface, abnormal water-bearing position, detailed lithology information and water-conducting channel distribution in the study area, so as to complete the identification and evaluation of the lithology characteristics and abnormal structure distribution of the study section. In addition, the study used the joint interpretation results to analyze the mechanism of water and mud inrush in the study section from the aspects of structure and mechanics, and evaluated the possibility of water and mud inrush in the study section. The method proposed in this paper effectively identifies and evaluates the distribution of clastic rock and water-bearing breccia in front of the tunnel face, and effectively avoids the occurrence of tunnel geological disasters.