Risk Assessment of Tunnel Face Instability under Multi Factor Coupling Based on Conditional Probability and Tunnel Construction Mechanics

The factors leading to the collapse of tunnel face are diverse, and there is an interaction relationship between multiple influencing factors at the physical and mechanical level. By analyzing the coupling relationship between the factors affecting the instability of tunnel working face, this paper deduces the calculation method of the coupling effect of tunnel construction risk factors for a certain risk event based on conditional probability theory, and makes reasonable assumptions on the monitoring data and risk probability. Finally, it is verified by a model test. The results show that the tunnel construction risk factors have a coupling effect by affecting other risk factors or changing the physical and mechanical parameters of surrounding rock, in which the coupling amplification effect will significantly change the failure probability of the risk carrier, so it is unfavorable to the stability of the tunnel face. The coupling amplification effect of risk factors will cause the increase of tunnel face extrusion deformation. Even if it causes a small deformation increment, it can also make the transition of risk probability and grade of tunnel face unstable, and cause tunnel face instability collapse. The research results of this paper can quantitatively evaluate and predict the stability of the working face in the process of tunnel construction.