Unsteady fractional stress relaxation time effect model

The study of rock stress relaxation characteristics is an important aspect of the research of its long-term mechanical characteristics. It is also the key to ensure the long-term safety and stability of the surrounding rock of the high-ground-stress roadway. Using the MTS815.02 triaxial test system, the stress relaxation test of the sandstone of Fuxin Hengda Coal Mine with a confining pressure of 30 MPa is carried out. A new unsteady fractional stress relaxation aging constitutive model is established by constructing the relationship between damage variables, time, and model parameters and considering that the fractional order is affected by the time effect. The correctness and rationality of the model are verified by experimental data. Test results show that as the relaxation damage develops during relaxation, the relaxation has evident nonlinear characteristics. The model curve is highly consistent with the experimental curve, which indicates that the unsteady model is suitable for reflecting the deformation of rock stress relaxation. It can better describe the whole process of stress relaxation change. This study can provide a scientific basis for the long-term stability analysis of Fuxin Hengda high in situ stress sandstone roadway.