Numerical simulations of the void distribution characteristics of crushed rock masses in mine gobs

Abstract

The internal stress levels of the crushed rock masses will change the movement states of the rock masses in the gob, and then affect the void distributions of crushed rock mass, and finally change the flow of gas in the gob. In this study, under the Lagrange framework, based on a discrete element method and a Hertz-Mindlin contact model, self-programming was used to simulate the compaction processes of a rock mass in mining gobs. The compression amounts were set as 0%, 5%, 10%, 15%, 20%, and 25%, respectively. The effects on the void distributions of the crushed rock masses of the internal stress levels of the crushed rock masses under the external load conditions were examined by changing the motion state of the rock blocks within in the gobs. The results showed that during the compression processes, the external loads could not be uniformly transmitted from the top of the crushed rock masses to the lower sections. Therefore the stress levels in the upper sections of the crashed rock masses were significantly higher than those of the lower sections. In addition, due to the rock blocks in the upper section of the crushed rock masses experiencing higher degrees of interference from the external forces, the sliding speeds of the upper rock blocks were also larger. At the same time, the rock blocks in the upper sections of the crushed rock masses tended to slide downward down longer. The migration of the rock blocks caused the upper rock blocks to become densely packed, and the coordination numbers of the rock blocks were large. However, the lower rock blocks were loosely distributed, and the coordination numbers of the rock blocks were small. This resulted in the void ratios in the lower sections of the crushed rock masses being higher than the void ratios in other layers of the crushed rock masses, with the void ratios of the lower sections of the rock masses determined to be 1.1–1.4 times that of the upper sections.