Study on voidage distribution regulation and formation mechanism ofcrushed rock mass in gob

The transfer and evolution of stress between rock blocks will change the compactness of crushed rock mass 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 paper,a discrete element method was used,along with the Hertz-Mindl in contact model and self-programming.The compaction processes of crushed rock mass composed of rock blocks with diameters of 0.6 0.8 and 1.0 m were simulated,with axial strains set at 0、0.05、0.10、0.15、0.20,and 0.25%,respectively.The goal of this study was to study how the internal stress of crushed rock mass in the gob affected the void distribution of crushed rock mass by changing the contact network between the rock blocks.The results showed that the stress in crushed rock mass was transmitted through the contact network between the rock blocks,and as the axial strains increased,the stress in the crushed rock mass increased gradually,and the contact network that transmitted the stress became denser.During the compression process,the external load could not be uniformly transmitted from the top of the crushed rock mass to the lower part,so that the stress in upper part of the crashed rock mass was significantly higher than the lower part.As the axial strains increased,the range with large contact force between the rock blocks gradually expanded from the upper part of the rock mass to the lower part.Because the rock blocks in the lower part of the crushed rock mass wasless interfered by the external force,the contact network between the rock blocks in the lower part of the crushed rock mass was looser,and the coordination number of the rock blocks in the lower part of the crushed rock mass was small.The void rate of the crushed rock mass decreased sharply from bottom to top,and then slowly decreased.Under the natural accumulation condition,the stress generated by the self-weight of crushed rock mass was small,and the coordination number of rock blocks in different layers was relatively small,so that the voidage at the bottom of the crushed rock mass was only 1.1 times that in the upper of crushed rock mass.However,under compaction conditions,the stress in different layers of the crushed rock mass had a large difference,and the coordination number of the rock blocks at the bottom of crushed rock mass was much smaller than that of the upper part,so that the voidage at the bottom of the crushed rock mass was 1.4 times that in the upper of crushed rock mass.