Experimental validation of three-dimensional discontinuous deformation analysis and its application to boulder-induced rockfall kinematics at a tunnel entrance

Rockfall hazards pose serious threats to engineering infrastructure in mountainous regions due to the high energy and destructive potential of moving boulders. This study investigated boulder movement at the entrance of the No. 2 transverse tunnel of the Layue Tunnel along the Sichuan–Xizang Railway using three-dimensional discontinuous deformation analysis (3D DDA). Physical experiments employing concrete blocks of different shapes and a marble slab slope were conducted to validate the numerical simulations. Corresponding 3D DDA models were developed to reproduce block movements under various geometric conditions, and displacement– and velocity–time histories were analyzed. A site-scale numerical model incorporating unmanned-aerial-vehicle-derived terrain data was further established to simulate the movement of a large boulder. Experimental and numerical results showed strong agreement, confirming the capability of 3D DDA to accurately capture rockfall kinematics. The boulder exhibited complex three-dimensional motion characterized by sliding, collision, bouncing, and flipping. Simulation results indicated that the boulder passed close to the tunnel entrance construction area before stopping in a river. The resultant displacement reached 135.43 m, with a maximum kinetic energy of 70.37 MJ and a total movement duration of 10.80 s. The study demonstrates the effectiveness of 3D DDA for rockfall hazard assessment and mitigation.