Abstract
Fracturing and fragmentation of rock blocks are important and universal phenomena during the propagation of rock avalanches. Here, the movement of a rectangular rock block characterized by different joint sets along an upper inclined and lower horizontal traveling path is simulated, aiming to quantify the fracturing and fragmentation effect of the block in propagation. The preset of the joint sets allows the block to break along the weak joint planes at the very beginning of fragmentation. With this design, the fracturing and fragmentation processes in the sliding rock block and their influences on energy transformation in the system are investigated. The results show that fragmentation can alter the horizontal velocities and kinetic energies of fragments in the block system with the front subblocks being accelerated and the rear part being obviously decelerated. Such energy conversion and transfer between the front and rear subblocks is attributed to the elastic strain energy release and transformation caused by fragmentation. The energy transfer induced by fragmentation is more efficient than that induced by collision. A positive trend between the kinetic energy increase of the front subblocks induced by fragmentation and the rock strength can be fitted well with a linear function. However, no good relationship is reached between the strain energy incremental ratio and travel distance, which implies that the fragmentation effects may be weakened with the increasing complexity of the fragmenting rock mass system. Three elastic strain wave release effects caused by rock fragmentation are further inferred and discussed based on simulation results.
Highlights
25 Rock avalanches are one of the most destructive geophysical flows and can effectively shape mountainous landscapes on Earth and other planetary surfaces (Lucas et al, 2014; Crosta et al, 2018)
The movement of a rectangular rock block characterized by different joint sets along an upper inclined and lower horizontal traveling path is simulated, aiming to quantify the fracturing and fragmentation effect of the block in propagation
When the joint in the middle of a rock block cracks, the front subblock gains additional kinetic energy, while the rear subblock loses part of its kinetic energy, leading to a long travel distance for the distal part. These kinetic energy variations are due to elastic strain energy release during fracturing, which is similar to the momentum transfer process caused by collisions in a multiblock system
Summary
25 Rock avalanches are one of the most destructive geophysical flows and can effectively shape mountainous landscapes on Earth and other planetary surfaces (Lucas et al, 2014; Crosta et al, 2018). They have caused numerous casualties and large economic losses in recent decades due to their extremely long travel distances (Evans et al, 2007; Fan et al, 2017). Hypermobility, i.e., exceptionally long runout distances of rock avalanches, is usually quantified by the apparent friction coefficient (H/L, where H and L represent the vertical and horizontal distances between the crest of the failure mass and the 30 distal point of deposition, respectively) (Heim, 1932).
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