Investigation on the failure mechanism of a tunnel entrance high-steep slope with ultra-large wedge blocks based on discrete element method.

An unstable wedge block with a volume of approximately 1,200,000 m3, intersected by an anti-dipped large fault and two outward-dipped faults, has been identified on the high-steep slope at the entrance of the tunnel spillway of the Shuangjiangkou hydropower station in China, a region characterized by high tectonic stresses. In this study, kinematic analysis was first conducted to preliminarily assess the possibility of block sliding, and then a three-dimensional discrete element code (3DEC) was utilized to analyze the mechanism of block instability during sequential excavation and reinforcement. The results showed that block sliding is caused by continuous excavation and deterioration of the mechanical properties of the bottom sliding surface. The failure behavior of the slope is primarily governed by the wedge block, which slides along the intersection line of two outward-dipped faults. After the excavation of Layers 1–4, the shear displacements of the faults exhibited accelerated and abrupt characteristics. Finally, the pretension cable proved effective in restraining block sliding, increasing the factor of safety for the slope from 1.16 to 1.28 after complete excavation and reinforcement. This study offers significant insights into the analysis of failure mechanisms in similar engineering challenges. [ABSTRACT FROM AUTHOR]