Effect of geometric obstructions, particle size distribution, and release angle on the mobility and deposit distribution along the runout zone of rock avalanches

Abstract This study determined the effect of various geometric obstructions, particle size distribution (coarse, fine, and uniform), and release angles (40°, 50°, and 60°) on the mobility and deposit distribution along the obstructions (concave and convex) in the runout zone of rock avalanches using Discrete Element Modelling, with which particle-particle and particle-wall interactions can be naturally captured. The results indicate that the convex and concave obstructions for coarse gradation at a release angle of 40° reduced the mobility of the slide by 40% and 33% and increased the duration of the slide by 20% and 18% compared to plain geometry, and similar behaviour was observed for uniform and fine graded particles. In addition, as the release angle increases, the velocity increases and the duration of the slide decreases for all types of gradations and geometric obstructions. Moreover, the particles get airborne after hitting the convex obstruction, whereas for concave obstruction, particles move in the form of an anticlockwise whirlpool inside the obstruction and try to escape from the upstream edge. The airborne characteristics such as jump distance, airborne time, and maximum jump height of particles greatly vary with the release angle. In comparison, the escape velocity of particles from a whirlpool is not influenced by gradation or release angle. Furthermore, the deposition of particles along the obstruction is different from that in the valley and is greatly influenced by the release angle. The study will help understand the interaction of sliding material with natural obstructions in the runout zone by considering various particle sizes and release angles.