Analytical model for tunnel face stability in longitudinally inclined layered rock masses with weak interlayer

In nature, rock masses often present non-horizontal layered characteristics due to geological tectonics. Tunnelling in such rock formations threatens and reduces the stability of the tunnel face. In addition, the existence of weak interlayer poses a potential threat to stability. In this study, an analytical model is established to comprehensively consider the influence of rock layer inclination and weak interlayer on the stability of the tunnel face. Then the virtual supporting force is obtained using the upper limit theorem of kinematic limit analysis with the nonlinear Hoek-Brown yield criterion. The optimal upper-bound solution is examined by the Genetic Algorithm. Several design charts are provided to analyze the effects of the tunnel diameter, inclination angle and weak interlayer on the stability of a tunnel face. The obtained results show that the instability of the tunnel face increases significantly due to the container of the weak interlayer. And the parameters of the lower-layer play a crucial role in the collapse of the tunnel face. Moreover, the effects of the position and thickness of the weak interlayer on the stability of tunnel face are discussed. The critical angle for the inclination of the rock layer leading to the most unstable state is remarked.