Study of stress relaxation properties of soft rock is an important aspect of long-term mechanical property

which is very important to keep soft rock tunnel long-term stability. The stress relaxation test of red silty mudstone under triaxial compression with confining pressure of 30 MPa is carried out on TLW-2000 triaxial rheological machine. The test results show that: with the deterioration of material properties and relaxation damage evolution

the process of stress relaxation is nonlinear. By analyzing the damage energy dissipation during stress relaxation

a new relaxation damage equation is established. And

a nonlinear relaxation model is established by introducing the damage factor into Nishihara model. The fitting results of stress relaxation test show that the stress relaxation properties are well reflect by this model. The research results provide a scientific basis for long-term stability analysis of soft rock tunnel for Yichang-Badong Expressway.