Damage mechanism of tunnel base heave under interlayer weakening effect in nearly horizontal layered rock

Abstract

The damage mechanisms and mechanical behavior of tunnel base heave in nearly horizontal layered rock were researched in this paper through three perspectives: causal analysis, mechanical analysis, and sensitivity analysis. Firstly, through field tests and laboratory experiments, it was found that the layered rock mass with structural planes being significantly weakened due to continuous groundwater infiltration, leading to heave deformation of the tunnel base subject to horizontal geostress. Then, the mechanical model for buckling instability of a layered rock structure was established to derive the deflection curve under interlayer load and the limit state buckling equations of the layered rock mass. Theoretical results indicate that the critical buckling instability load of layered rock masses is related to the horizontal stress and their structural and material characteristics, while the interlayer load influences the deformation before buckling. Meanwhile, by incorporating a discrete element numerical model employing the Bonded Block Model to represent the multi-layered structural planes, the interlayer load pattern and the base heave deformation were determined. Finally, the stability coefficients were calculated by using the critical buckling load equations for several typical cases of high-speed railway tunnels to identify the transition of the instability state of layered rock mass. The analysis of instability state of tunnel base and the sensitivity of influencing factor provides a reference for identifying and mitigating the base heave for the high-speed railway tunnel.