A multiscale mesoscopic model for investigating the evolution characteristics of tunnel lining cracks and the variation of local bearing capacity

Understanding the load-bearing capacity of tunnel lining is crucial for ensuring safe operation. However, obtaining accurate spatial parameters of cracks remains challenging, even though surface crack characteristics are easily accessible. Refined numerical simulations has thus become an important approach for state-evaluation and long-term predicting. Combining model tests with concurrent multi-scale model based on mixed-mode fracture control theory, this study analyzed mixed fracture modes of tunnel lining. Conditions were set to reveal the influence of loading paths on failure mechanism. Results indicate that the crack propagation exhibits significant three stage characteristics: crack-free, Type I-crack, and Type Γ-crack. Differences exist in the crack propagation stages under different loading paths; the strength of horizontal constraints is positively correlated with the height of the compression zone and the plastic hinge region of the structure. In Γ-type crack stage, the residual bearing capacity decreases sharply, the crack width increases rapidly and penetrates. This stage is therefore critical, leading to local instability and spalling. Based on these findings, a formula was developed to predict crack depth from crack width, considering the influence of surrounding rock constraints. This enables rapid assessment of the local bearing performance of tunnel linings based on observable crack features.