Numerical modeling of the time-dependent development of the damage zone around a tunnel under high humidity conditions

A coupled mechanical and diffusion model is proposed to determine the instantaneous and time-dependent elastoplastic behaviors of rock under high humidity conditions and model the time-dependent development of an excavation damage zone (EDZ). Time-dependent deformation is a macroscopic consequence of the progressive damage caused by stress and the degradation of the elastic modulus and strength of rock. An experiment is designed to verify the numerical model, and good agreement is observed between the experimental and numerical results. The time-dependent deformation of specimens at different stress levels is simulated to study the sensitivity of the results to the stress level. The influence of joints on the development of an EDZ is studied based on the proposed numerical model. The application of this numerical model to the in situ development of an EDZ in the headrace tunnel of the Jinping II Hydropower Station indicated that the support system did not prevent the development of the EDZ but effectively prevented the deformation of the surrounding rock under high humidity conditions. The conclusions of this study provide some guidelines for designing underground openings under highly humidity conditions.