Theoretical unloading fracture mechanism and stability analysis of the slope rock masses in open-pit mines

Instability of the rock slopes in open pit mines during the excavation unloading is an increasingly serious problem in the field of slope engineering. To explain the mechanical mechanism of slope unloading damage from a theoretical point of view, a simplified mechanical model of slope excavation based on the theory of fracture mechanics and the rock strength damage criterion is established. The damage process of the slope under excavation disturbance is dynamically analyzed by combining the interstructural characteristics of the slope. The solution equations for the extent of the plastic zone at the end of the crack of the excavated slope and its propagation length are derived. Calculation method of unloaded slope stability coefficient is proposed based on the mechanical model of crack propagation. The results show that (1) the stress intensity factor (SIF) at crack end in the slope under the action of unloading was larger than that under the original condition. (2) The range of the plastic zone at crack end in the slope rock mass can be attributed to the slope height, inverse logarithmic function to the slope angle, positive proportional function to the crack length, and the periodic fluctuation function of the crack angle. (3) The slope safety factor (SF) was found to be negatively related with the slope angle, slope height, crack angle, and the crack length unloading factor and positively related with the friction factor. Finally, the reasonableness of the theoretical derivation is verified by an engineering case study.