Fragmentation Modes and Crack Evolution of Jointed Rock During Rockfall Impacts: Insights from Parallel DDA Simulations

Joints are one of the most important factors that influence the fragmentation mode of rocks during impact. Using physical experiments and an OpenMP-based parallel discontinuous deformation analysis (DDA) incorporating virtual joints, this study investigates crack propagation mechanisms and fragmentation modes in rocks with various joint distribution patterns during rockfall impacts. The results indicate that (1) the degree of rock fragmentation can be quantitatively described by the surface area ratio of the equivalent volume sphere ( η ). η increases with increasing joint connectivity rate ( k ), decreases with increasing joint-slope angle ( β ), and tends to increase with increasing joint spacing ( s ). But when k is low, η decreases once s increases to a critical threshold. (2) Rockfall fragmentation modes can divided into three categories according to the destructive morphologies of rocks with different joint distributions. (3) The degree of particle fragmentation within the joint set ( ρ ) quantitatively characterizes the rockfall fragmentation mode. The inherent factor that determines the rockfall fragmentation mode is the length-to-width ratio, b , of the blocks between joints. (4) The three failure modes are internal fragmentation within joint sets ( b  < 0.25 and ρ  > 0.2), expansion along outlines of joint sets (0.25 ≤  b  ≤ 1 and 0.01 ≤  ρ  ≤ 0.2), and expansion along specific joints ( b  > 1 and ρ  < 0.01). (5) Different joint geometric parameters significantly affect fragment energy and velocities after impact. This study can serve as a reference for particle fragmentation mechanisms in rocks with inherent joints.