The Height and Scope of Overburden Fractured Zone of Thick Coal Seam Based on Different Gob Behavior for a Case Coal Mine in China

Abstract

Due to the extraction of thick coal seam, there will be three main zones formed above the extraction space: caved zone, fractured zone and continuous deformation zone, as the fractured zone is full of vertical and horizontal fractures, and these fractures consist of the gas channel for gas flow, and it can be used for gas drainage to eliminate gas disaster, so the objective of this paper is to find the effect of different gob behavior to the height and scope of the fractured zone. Firstly, the factors that affect the change of fractured zone are discussed, the empirical equation is used to estimate the height of the fractured zone in the case coal mine, then three finite models with different gob behavior are built to solve this problem, these three gobs are filled with rockmass that has variable Young’s modulus, the results show that the model with Gob3 has the largest stress recovery distance and the largest height and scope of destressed zone (fractured zone), and its stiffness is much smaller, finally, a field study is carried out in 4314 working face of Changping colliery, four boreholes are drilled in the different location of the gob roof, the data shows that No. 2 and No. 3 boreholes have larger gas concentration than No. 1 and No. 4 boreholes, it indicates that the height of the fractured zone is much closer to 43 m, the field measurement results are exactly consistent with numerical simulation result of Gob3, and Gob 3 is the more realistic gob for the case mine, it has a recovery distance of 76.5 m—0.17 times mining depth.