Contribution of rock strength to post-fragmentation spreading and deposition of rockslides

Fragmentation is a common phenomenon in the runout process of large rockslides. Rocks have different strengths under the influence of the rock type and weathering degree, resulting in varying fragmentation characteristics. However, the limited understanding of how rock strength influences the post-fragmentation kinematic characteristics of rockslides is limited. Taking a natural rockslide as an example, this paper quantitatively analyzes the runout and deposition of the rockslide using the discrete element method (DEM) and examines the impacts of the rock strength on the runout and deposition characteristics of the rockslide. The results reveal that (1) Rock strength significantly influences fragmentation and runout characteristics: medium-to-high strength rocks exhibit two-stage fragmentation (10-20 s and 55-65 s), while weak-strength rocks achieve 98% fragmentation within 20 s. Optimal kinetic energy conversion occurs in medium-strength rocks, with a maximum velocity difference of 39.3 m/s between the anterior and posterior edges. (2) The sudden change in the cross-sectional dimensions of high-strength rocks under a high spreading velocity (>60 m/s) may amplify air blast hazards. (3) Deposition patterns reveal that the spatial distribution of fragments preserves original positional order; high-strength rocks produce larger fragments (nominal fragment size increases from 0.028 of weak-strength rocks to 0.607); and centroid displacement increases from 1907 m to 2117 m with rock strength in open terrains. (4) Energy dissipation analysis shows that frictional dissipation (>60%) > collisional dissipation (~37%) >> fragmentation dissipation (<2%) in the process of rockslide runout. The rock strength induces <5% variation in partitioning of energy dissipation.