Mechanisms of slope instability induced by two-hole oversized tunnels with small clearances underneath

Abstract

The double-tunnels crossing potential landslides are gradually developing towards smaller clearances and larger cross-sections. The disturbance of the tunnel construction is very likely to cause slope instability, tunnel damage, and other natural disasters. In the paper, model tests and numerical analysis are applied to investigate the instability mechanism of landslides caused by double-tunnels with oversized sections orthogonally beneath, based on the Shaoxin High-Speed Hanshankou Tunnel. The mechanism of tunnel-induced landslides is obtained and the stability factor of safety is modified by strength reduction and parametric analysis. The results indicate the following: The superimposed effect of double-hole excavation and the disturbance of surrounding rock caused by super-large cross-section excavation are the two main reasons for the landslide in Hanshankou Tunnel. The degree of influence of various factors on the stability of the tunnel-landslide mass is: section size > buried depth > clear distance > construction method > support parameters. It is recommended to use the formula F=α1α2α3Fst to modify the slope stability safety factor.