Study on the deformation and failure mechanism of tertiary water-rich soft rock tunnels based on the moisture migration-fracture coupling model

Abstract

In Tertiary mudstone formations, the surrounding rock of soft rock tunnels is highly susceptible to large deformations and failures due to moisture migration, presenting significant safety risks during both construction and operation. To address this issue, this study develops a moisture migration-fracture coupling model based on the Finite-Discrete Element Method (FDEM) to simulate and analyze the effects of moisture diffusion on the deformation and failure mechanisms of tunnel surrounding rock. Through numerical simulations considering factors such as moisture diffusion range, gravel layer thickness, and angle, the study investigates the impact of these parameters on the spatiotemporal distribution of moisture content, deformation characteristics, and crack propagation in the surrounding rock. The results indicate that moisture diffusion significantly enhances both deformation and crack formation, with the most significant damage occurring at the arch waist. As the moisture diffusion range and gravel layer thickness increase, the arch foot and arch shoulder are more prone to damage. Moreover, an increase in the gravel layer angle heightens the susceptibility of the arch foot and arch shoulder to failure. This study reveals the deformation and failure mechanisms of expansive rock layers under moisture migration, providing theoretical support for stability assessment and support system design in soft rock tunnels, with significant engineering applications.