The effects of rockfall volume on runout distance

Abstract

The main goal of this paper is to clarify the effects of rockfall volume on its fluidization. For this purpose, outdoor rockfall experiments were carried out to analyze runout distances and individual movements of rockfall blocks and numerical simulations were conducted for these experiments to learn more about the mechanism of rockfall fluidization. The rockfall experiments were conducted using an artificial slope on which granite slabs were surfaced and overlaid with cubiformed granite blocks. The size and number of blocks were varied in this series of experiments. Further, numerical simulations were carried out in which the coordinates of individual rockfall blocks were traced in three-dimensional space from rockfall initiation to final deposition. It became clear from the experiments and simulations that the runout distance had a positive correlation with the rockfall volume (number of rockfall blocks) and the runout distance of the gravity center of deposited rockfall mass had a negative correlation with the rockfall volume. To clarify the mechanism of these two phenomena, the positions of individual blocks from initial arrangements to final depositions were traced in the experimental and numerical simulations. This revealed that the relative positions of each block along the slope direction were not changed during rockfall movement. The reason for the block-sequence preservation was that front facing blocks in the initial cube arrangement accelerated and rear facing blocks decelerated along the slope by internal collision between blocks. Further, as the rockfall volume increased, the opportunities for impact among the rockfall blocks increased with the front facing blocks pushed farther. Whereas the gravity-center of the deposited rockfall mass had an inclination to travel shorter distances as rockfall blocks increased according to the increase of kinetic energy dispersed by the collision of blocks.