Study on triaxial creep mechanical properties and creep model of sandy mudstone with initial radial depth damage

The unloading effect from roadway excavation creates a stress gradient field in the surrounding rock, extending from the edge to the far end of the roadway. This leads to depth damage and destruction in the surrounding rock along the radial direction. The coupling between radial depth damage and the rheological behavior of the surrounding rock results in uncontrollable deformation of the roadway's surrounding rock. To investigate the creep development mechanism of sandy mudstone influenced by radial depth damage, we design a stress path that simulates roadway excavation. Specimens are prepared under various radial depth damage states, the Weibull distribution's statistical damage theory is introduced, the radial depth damage factor is defined, and the constitutive equation for radial depth damage in sandy mudstone is derived. Triaxial compression creep tests were conducted on sandy mudstone with radial depth damage, leading to the establishment of a nonlinear creep constitutive model that incorporates both initial radial depth damage and creep damage. Results indicate that the extent of radial depth damage significantly influences creep deformation during the nonlinear creep stage. The model proposed herein aligns well with the creep test curves of sandy mudstone, effectively capturing the complete creep behavior of radial depth-damaged rock samples. Moreover, its fitting accuracy surpasses that of the Burgers and the enhanced Nishihara model. These findings offer valuable insights for predicting the creep response of damaged surrounding rock and for designing roadway support systems.