A new stability analysis model for wet-dry sensitive rocks surrounding underground excavations based on disturbed state concept theory

The assessment of long-term stability of rocks surrounding a tunnel considering rock weathering is a challenging topic in tunnel engineering. In this study, a new stability analysis model for wet-dry (W-D) sensitive rocks surrounding underground excavations is presented. Based on the disturbed state concept (DSC) theory, the excavation disturbed zones (EDZ) of a tunnel are defined and their evolution characteristics during the tunnel excavation stage and the operation stage are analyzed. Based on the characteristics of the damage and stress states of rocks at different deformation stages, the concept of disturbance in the DSC theory is extended and the concepts of elastic disturbance and plastic disturbance are proposed. Both disturbance functions are derived based on the Mohr-Coulomb yield criterion considering the W-D rock weathering deterioration. From these functions, a DSC-based stability analysis model for W-D sensitive rocks surrounding underground excavations is established. The proposed model is implemented in the finite difference software FLAC3D and verified using a simple numerical model. As a case study, the effectiveness of the mitigation measures for the problematic section of the South Lvliang Mountain Tunnel is evaluated by the proposed model. It has been demonstrated that the formation of EDZ around the tunnel is a dynamic process which gradually evolves with the tunnel excavation, operation and weathering deterioration of surrounding rocks. The proposed stability analysis model can better analyze the disturbance evolution characteristics of W-D sensitive rocks surrounding a tunnel over its full life cycle and is a more comprehensive evaluation tool for tunnel stability assessment considering rock weathering deterioration.