Instability Mode Analysis of Surrounding Rocks in Tunnel Blasting Construction with Thin Bedrock Roofs

Abstract

The thin bedrock roof tunnel is widely distributed in China, and its influence of blasting construction on surrounding rock is obviously different from that of ordinary homogeneous surrounding rock tunnel. In order to control the safety of tunnel construction under the condition of thin bedrock roof effectively, the method of the numerical simulation is adopted to establish 6 models with the bedrock roof thickness of 5, 4, 3, 2, 1 and 0.5 m respectively, and research the vibration distribution characteristics of tunnel surrounding rock caused by blasting construction. The stability of tunnel surrounding rocks with different bedrock roof thickness is analyzed according to the influence partition of blasting vibration, and the corresponding instability mode is proposed. The results show that: when the roof thickness is 5 m or more, the surrounding rock is stable; when the roof thickness decrease to 4 m, the whole bedrock roof on the most unstable transverse section (1 m behind the tunnel face) produces slight tensile spallation; when the roof thickness decrease to 3 m, part of bedrock roof on the most unstable transverse section produces serious stretching cracks and radial cracks, the possible instability mode is over excavation; when the roof thickness decrease to 2 m and below, the stability of surrounding rock is poor, the possible instability mode is collapse or falling within 1 m behind the tunnel face.