An Analytical Solution for the Excavation Disturbed Zone in Wet–Dry Sensitive Rock Tunnels Based on the Disturbed State Concept Theory

Assessing the stability of rocks surrounding a tunnel, particularly with consideration of rock weathering, is a significant challenge in tunnel engineering. This study proposes an analytical solution for the excavation disturbed zone (EDZ) in tunnels constructed in wet–dry (W-D) sensitive rocks. Based on the disturbed state concept (DSC) theory, the EDZ of a tunnel is defined, and its evolution characteristics under the action of W-D cycles is analyzed. Based on the damage and stress states of rocks at different deformation stages, the EDZ is divided into elastic disturbed, plastic disturbed, and fully disturbed zones. On this basis, a constitutive model for W-D sensitive rocks is established using DSC theory, incorporating the negative effects of cyclic W-D rock weathering. This model serves as the cornerstone for deriving a theoretical analytical solution that captures the disturbed zoning of the EDZ in a circular tunnel subjected to uniform stress fields under cyclic W-D conditions. Additionally, the influence of W-D cycles and flow rates on the disturbed zoning of gypsum rocks surrounding the tunnel is further discussed. The findings reveal that the formation of the EDZ around the tunnel is a dynamic process that extends throughout the tunnel's lifecycle, from excavation to operational phases. The proposed DSC-based model effectively characterizes the mechanical response of W-D sensitive rocks. The theoretical solution for the EDZ in W-D sensitive rock tunnels provides a valuable tool for analyzing the evolution characteristics of EDZ disturbance and assessing tunnel stability, especially when considering rock weathering deterioration.