Abstract: To investigate macro-mechanical parameters of a rock mass slope in Jinping during unloading, a series of unloading experiments on sandstone is carried out in the laboratory. The results show that there is degradation effect on strength and deformation parameters of rocks in unloading process compared to loading failure, and there exist different deformation and failure characteristics under low and high confining pressure. Therefore, based on correction of slope mass rating (SMR) and conventional SMR (CSMR), an evaluation system of unloading rock mass-USMR (Unloading Slope Mass Rating) has been proposed. In this procedure, the excavation method, slope form and unloading damage are considered. Based on USMR, a dynamic analysis of macro-mechanical parameters (deformation modulus Em, compressive strength , tensile strength , and shear strength parameters cm and ) of unloading slope rock mass is made, the effects of different confining pressures and unloading damages (De) on deteriorating law of the parameters of rock mass are examined. The analysis results indicate that in the process of excavation unloading the macro parameters of rock mass degrade in different degrees. The degradation laws of rock mass parameters vary in tensile stress area, low stress area and high stress area. Mechanics parameters of rock mass are more sensitive to excavation unloading in the tensile stress area and low stress area. The results will benefit the stability analysis of slope unloading excavation.

Key words: unloading, macro-mechanical parameters, unloading slope mass rating, degradation effect