Influence of intergranular friction weakening on rock avalanche dynamics

Abstract

In this paper, we investigated the significance of intergranular friction weakening on the dynamics of the Jiweishan rock avalanche. First, high-velocity-friction tests simulating the shearing between the surfaces of adjacent grains were conducted to obtain a model of friction weakening of grains inside granular debris during transport. Then, the model was incorporated into an improved discrete element method that could consider intergranular friction weakening to simulate the dynamic course of the Jiweishan rock avalanche. Finally, we compared the results from the numerical models with and without granular friction weakening to investigate its influence on the dynamics of the rock avalanche. The results of the high-velocity-friction tests revealed that intergranular shearing could significantly reduce the friction of granular surfaces; this was determined by the overall results for normal stress, shear velocity and shear displacement. Our modeling results indicated that the rapid increase in normal stress and shear velocity were the main reasons for the rapid decrease in intergranular friction coefficients in the falling and collision stages. However, the friction coefficients further decreased due to increasing shear displacement between rock debris in the flowing stage. Furthermore, obvious intergranular friction coefficient distribution characteristics in rock avalanche deposits could be observed from our modeling; they tended to decrease with increased depth in the deposit and increasing distance from the source. With intergranular friction weakening, a faster velocity (∼10.0–15.5 m/s) and a longer transport time (∼12–44 s) of the rock debris were modeled due to the lower frictional energy consumption caused by intergranular friction weakening. Finally, the transport distance considering intergranular weakening was ∼ 395–711 m longer than that without weakening. Further analysis showed that intergranular friction weakening may be applied to explain the high mobility of rock avalanches. The results of our study may improve predictions of the speed and travel distance, and consequently the risk assessment, of widely distributed rock avalanches worldwide.