## 1 Introduction  
The growing demand for hydropower resources in China has led to the progressive expansion of hydropower infrastructure to regions with extremely complex geological conditions, such as the Qinghai-Tibet Plateau. The BDa Hydropower Station is situated in the southeastern region of the Qinghai-Tibet Plateau. The area is shaped by intense tectonic activity within the early crust and the unloading of rock masses caused by valley cutting. Hence, the shallow rock masses on the slopes of the dam site area and its surrounding areas are subjected to the dual effects of plateau freeze-thaw cycles and weathering erosion, which result in the formation and extensive distribution of large-scale cataclastic loose rock masses [1, 2, 3, 4]. Owing to their fragmented and loose structural characteristics, these rock masses exhibit pronounced loose deformation and low self-stability, becoming unstable under external forces and posing a serious threat to the safety and integrity of engineering operations. During the construction of the Bda Hydropower Station, excavation activitiesassociated with the original mixing station project and local collapse led to the disturbance of the SL12 (rock coding) cataclastic loose rock mass, affecting the construction of the hydropower station. Consequently, slope cleaning and excavation treatments became necessary to mitigated the associated risks. Conducting a stability analysis of the cataclastic loose rock slope is thus of practical importance, not only ensuring the safety of hydropower station construction but also providing a typical case for an understanding of the mechanical behavior of rock masses in similar geological environments. To date, extensive research has been conducted on the distribution characteristics, genetic mechanisms, development laws, failure characteristics, seismic dynamic responses, and stability of cataclastic loose rock masses [5; 6; 7; 8; 9; 10; 11; 12; 13; 14]. [PERSON] [15] studied the strength characteristics of a cataclastic loose rock mass and evaluated its stability using empirical methods. [PERSON] [16] and [PERSON] [17] summarized the development and distribution characteristics, deformation and failure behavior, and formation mechanisms of cataclastic loose rock masses through a field investigation. [PERSON] [18] introduced novel technologies and methods, such as 3D laser scanning and unmanned aerial vehicle (UAV) image measurement, to conduct in-depth research on the development characteristics, physical and mechanical parameters, deformation, and failure characteristics of cataclastic loose rock masses. [PERSON] [19] used the finite element virtual power method to analyze the stability of broken loose rock slopes. Numerical simulations can replicate the deformation behavior and stability of slopes during excavation by incorporating the physical and mechanical properties of the rock and soil. This simulation method offers notable advantages, including flexibility, economy, and repeatability. Researchers have employed the discrete element simulation method to explore the potential deformation and failure process and the instability mode of rock-soil composite slopes under natural and seismic conditions [20; 21; 22; 23; 24; 25]. [PERSON] [26] used finite element numerical simulation software to calculate the excavation response characteristics of a cataclastic loose rock slope. However, the 3D discrete element numerical simulation of cataclastic loose rock masses in actual complex terrain is rare, especially for fractured loose rock slope excavation. Therefore, this study integrates the slope cutting and excavation treatment plan proposed by the design unit. First, a 3D real-life model of the cataclastic loose rock slope in the study area is constructed using UAV oblique photography technology. Then, the 3 DEC discrete element numerical simulation software is used to analyze the impact of slope cutting excavation on the stability of the cataclastic loose rock slopes in the mixing plant.