Abstract: The instability and failure of hazardous rock masses, along with the resulting geological disasters, pose significant threats to infrastructure construction and operation. This study focuses on a rock slope along the G318 National Highway in the Xizang Autonomous Region as its research background, analyzing the potential risks of hazardous rock masses in the area and identifying the characteristics of the primary controlling structural planes. Using unmanned aerial vehicle (UAV) photogrammetry, slope imagery is acquired and a dense point cloud is generated to construct a digital surface model. UAV photogrammetry is employed to acquire slope imagery and generate a dense point cloud for constructing a digital surface model. A three-dimensional laser scanner is utilized to obtain high-precision point cloud data of hazardous rock mass and create a triangulated surface model. The geometric information of secondary structural planes within the rock mass is identified and interpreted using the coordinate data from the point cloud. A three-dimensional discontinuous deformation analysis (DDA) numerical model of the slope and hazardous rock masses is developed, optimizing modeling efficiency and computational feasibility. The stability of hazardous rock masses and the spatial kinematic disaster mechanisms post-failure are quantitatively analyzed by integrating the failure process with time-history curves of block displacement and kinetic energy. The results indicate that the hazardous rock mass I initially fails in a sliding mode when time≤1.0 s, subsequently evolving into a combined sliding and rotational mode. Tensile cracks develop between the rear edge and the slope, while shear failure occurs at the interface between the rock mass and the bedrock. The violent sliding of block II-4 in hazardous rock mass II triggers a rockfall disaster, with the maximum combined kinetic energy of impact reaching 259.186 MJ. Meanwhile, blocks II-1, II-2, and II-3 exhibit cascading failure effects due to dislocation and crack propagation. The instability of hazardous rock mass I directly triggers the failure of hazardous rock mass II, which subsequently influences the motion and evolution of mass I, leading to mutual interaction and merging of collapse blocks. This results in the formation of a large-scale block system, significantly increasing the overall volume and impact potential of the rockfall. Integrating UAV photogrammetry and three-dimensional laser scanning as non-contact measurement technologies notably enhances the modeling accuracy and efficiency of the three-dimensional DDA method. This research elucidates the dynamic interaction mechanisms involved in hazardous rock mass collapse and provides a theoretical foundation and technical reference for preventing and mitigating hazardous rock mass disasters.

Key words: hazardous rock mass, instability and failure, three-dimensional discontinuous deformation analysis (DDA), unmanned aerial vehicle (UAV) photogrammetry, three-dimensional laser scanning