Abstract: The rheological properties of rock are of great significance to the analysis of long-term deformation and stability of slopes. Based on the sampling of construction site at a highway in Guizhou province, the graded unloading rheological tests under two stress paths including constant axial stress and unloading confining pressure, and equal proportional unloading of confining pressure and axial stress were designed. The test results show that under the two stress paths, the rheological trend of the mudstone specimen under unloading is basically the same. Under the failure stress, the lateral deformation of the mudstone sample increases rapidly and it exceeds the axial deformation, and the lateral expansion is more significant. Compared with the constant axial stress unloading condition, the equal proportional unloading requires a much longer time, and the axial deformation of the mudstone sample rebounds. However, axial and lateral deformation account for a large proportion of the total deformation, which is about twice of that in unloading of constant axial stress. It shows that under the equal proportional unloading of confining pressure and axial stress, the predictability in failure of rock sample is smaller, but its damage effect is much greater. The proportional design experiment refers to the actual slope excavation gradient is designed to carry out the proportional unloading test, which has great reference for the long-term stability analysis of the actual slope engineering.

Key words: constant axial stress unloading, equal proportional unloading, rheology