Dynamic Fragmentation of Jointed Rock Blocks During Rockslide‐Avalanches: Insights From Discrete Element Analyses

Abstract

The dynamic fragmentation of jointed rock blocks during rockslide avalanches has been investigated by discrete element method simulations for a multiple arrangement of a rock block sliding over a simple slope geometry. The rock blocks are released along an inclined sliding plane and subsequently collide onto a flat horizontal plane at a sharp kink point. The contact force chains generated by the impact appear initially at the bottom frontal corner of the rock block and then propagate radially upward to the top rear part of the block. The jointed rock blocks exhibit evident contact force concentration and discontinuity of force wave propagation near the joint, associating with high energy dissipation of granular dynamics. The corresponding force wave propagation velocity can be less than 200 m/s, which is much smaller than that of an intact rock (1,316 m/s). The concentration of contact forces at the bottom leads to high rock fragmentation intensity and momentum boosts, facilitating the spreading of many fine fragments to the distal ends. However, the upper rock block exhibits very low rock fragmentation intensity but high energy dissipation due to intensive friction and damping, resulting in the deposition of large fragments near the slope toe. The size and shape of large fragments are closely related to the orientation and distribution of the block joints. The cumulative fragment size distribution can be well fitted by the Weibull's distribution function, with very gentle and steep curvatures at the fine and coarse size ranges, respectively. The numerical results of fragment size distribution can match well some experimental and field observations.

On the Dynamic Fragmentation and Lubrication of Coseismic Landslides

“…indicate that under the current testing conditions (i.e., seismic and gravity loading) and the slope volume, the strong rock slope can effectively resist seismic shaking and basal shear-induced fragmentation. This finding can match well the numerical observations in Zhao et al (2018) on the dynamic fragmentation of intact and jointed rock blocks. Figure 14b summarizes the variations of peak vibrational (T pv ), rotational (T pr ) granular temperatures, and landslide frontal propagation velocity (v f ) with the particle bonding strength for seismic-induced and gravitydriven landslides.…”

Contributions of Rock Mass Structure to the Emplacement of Fragmenting Rockfalls and Rockslides: Insights From Laboratory Experiments

“…According to our additional 60 friction tests of sliding masses on matte paper, the variation in the friction coefficient caused by recurrent friction between the experimental materials and matte paper is very small and negligible during our 36 experiments. The sliding distance of the materials on the inclined slab (L) is 2 m. This kind of experimental model is similar to those used in previous slab experiments (Davies & McSaveney, 1999; Manzella & Labiouse, 2009; Bowman et al, 2012; Haug et al, 2016; Zhao et al, 2017, 2018), which allows us to compare our results with those from previous studies.…”

“…The formation of rock mass structures in the experiments is presented in Figure 1b. Inspired by Bowman et al (2012) and Zhao et al (2018), the structures simply include changes in the orientation, inclination, and spacing of the discontinuities (Glastonbury & Fell, 2010). Table 1 provides a detailed description for each test condition.…”

“…In their experiments, joint orientations were modeled by setting the different arrangements of source blocks. Following Bowman et al (2012), Zhao et al (2018) created more complex joint sets to investigate the dynamic fragmentation of jointed rock blocks during rockslides by discrete element method simulations. The results indicate that jointed rock blocks influence elastic wave propagation and energy dissipation when the blocks collide with the horizontal plane and finally affect the degree of fragmentation in the deposit.…”

A novel random discrete element analysis of rock fragmentation

“…The damping coefficient is determined by trial and error to ensure it has negligible influence on the overall dynamics of the rock sample. The choice is in line with the DEM model configurations in Zhao et al 27 and Zhao et al 28 The numerical iteration time step ( Δt ) is set as small as 2 × 10 −7 seconds to guarantee numerical stability. The vertical loading was applied by controlling the axial deformation of the rock sample at a constant strain rate of 1 per second.…”