AE counts–based nonlinear creep damage model for sandstone after high-temperature treatment and time-dependent deformation of tunnel surrounding rock
Abstract
Understanding the long-term creep behavior of sandstone after high-temperature treatment is crucial for the stability control of underground engineering subjected to thermal effects, such as deep geothermal development and nuclear waste storage. In this study, uniaxial and triaxial creep experiments were conducted on sandstone samples heat-treated at 800 °C, during which acoustic emission (AE) signals were continuously monitored. Based on the AE count evolution, a nonlinear creep damage constitutive model was developed. The finite difference form of the model was derived and implemented into FLAC3D via a user-defined constitutive routine. The proposed model was validated against experimental creep curves, demonstrating superior fitting accuracy compared with the improved Nishihara model. Using the established numerical approach, the instantaneous deformation of surrounding rock during tunnel excavation and the time-dependent creep behavior after excavation were systematically investigated. The damage and deformation evolution of the surrounding rock under unsupported and supported conditions were compared. Results indicate that applying shotcrete and anchor rod support reduces roof displacement by 76.4%, floor displacement by 34.2%, and sidewall displacement by 35.7% compared with the unsupported case. Moreover, the maximum principal stress increases and the stress concentration zone shifts closer to the tunnel surface under supported conditions. The proposed model effectively captures the accelerated creep stage and provides a reliable tool for evaluating long-term stability of tunnels in high-temperature rock masses.