Dynamic unloading zoning of excavated rock slopes and optimization of support design

The excavation of rock slopes generates a wide unloading zone, whose mechanical properties directly influence the safety and stability of the slope. This study conducts laboratory unloading tests on sandstone to analyze the damage patterns of rock samples during unloading. Using the unloading ratio as a zoning criterion, the damage degree of each unit during excavation is accurately assessed and weakened accordingly, which is then incorporated into numerical simulations of slope excavation to achieve dynamic unloading zoning. The proposed dynamic zoning method is used to study deformation and support design optimization of engineering rock slopes after excavation unloading. The results show that: (1) As the unloading ratio increases, the deformation modulus exhibits a stage-wise deterioration trend. When the unloading ratio is less than 50% of the total, the deformation modulus reduction is negligible; between 50% and 90%, the average modulus loss rate ranges from 6.8% to 16.9%; beyond 90%, the modulus sharply decreases, with an average loss rate of 16.9% to 42.5%, and the extent of modulus reduction during unloading failure increases with confining pressure. (2) Compared to compression tests, the cohesion of rock samples under unloading decreases by 32.9%, while the internal friction angle increases by 17.5%. (3) The application of unloading zoning results in significant increases in deformation and the plastic zone area of excavated rock slopes. (4) The zoning method for distinguishing damaged and undisturbed zones provides a basis for optimizing support depth. These findings offer valuable references for slope excavation unloading analysis and support design optimization.