Abstract: This paper presents a case history of a tunnel project. Throughout the field survey, highdefinition remote sensing and UAV aerial survey, etc., the topography, geological structure, rock properties, hydrogeological conditions of a tunnel entrance area were thoroughly investigated. The structural characteristics and deformation failure patterns of hazardous rock masses were analyzed by using the stereographic projection. Quantitative evaluation and three-dimensional simulations of the unstable rockfall trajectories and energy were performed after the qualitative analysis. which can provide a reference for similar engineering designs. The results show that the slopes in the area are high and steep, with well-developed structural planes, which provide conditions for the development of hazardous rock masses. The rock strata are cut by structural planes nearly parallel to the slope surface, resulting in poor rock mass integrity. There are steeply dipping structural planes at the rear edge of the rock mass, which, under the joint action of joints and bedding planes. The potential instability type of hazardous rock mass and boulder in the area is mainly toppling type. The hazardous rock mass in the area is generally stable under rainstorm and earthquake conditions; The three-dimensional simulation shows that the rockfall basically rolls along the groove on the slope surface, with the maximum trajectory bounce height of three meters and the maximum movement speed of 19.7m/s. The rockfall frequency at the tunnel entrance is medium, the rockfall bounce height is low (mainly sliding or rolling close to the ground), and the rockfall energy level is low to medium, with high risk, so protection needs to be strengthened. The research results can provide reference for similar engineering analysis.

Key words: Tunnel, Hazardous Rock Mass, Side Slope, Stability Analysis