Research on quality evaluation systems of slope rock mass based on degradation of unloading excavation

Three kinds of conventional evaluation systems were applied to evaluate the quality of unloading rock mass, and rock mass mechanics parameters in original and unloading condition were calculated respectively, so the deficiencies of conventional evaluation systems in evaluation of unloading rock mass quality was made clear. Accordingly, we put forward a new quality evaluation system of USMR method that is suitable for unloading rock mass. The presented system considers the basic rock properties included in normal RMR method, such as rock block condition, structural plane condition and spacing, groundwater, and also the slope dip and structural plane dip, relationship between slope proneness and structural plane proneness; besides, the factors of rock mass degradation such as excavation method, unloading damage and slope shape are taken into account as well. The cm value calculated by USMR is smaller than that of three conventional methods, which is accord with the actual condition. The results have certain guiding significance to rock mass stability analysis of high slope excavation engineering.