Abstract
Taking Pingbao Coal Mine as the engineering background, the stress distribution, surrounding rock displacement, and plastic zone distribution characteristics of a bottom gas extraction roadway are simulated by FLAC3D under multiple disturbances. The mining disturbance due to the overlying coal seam is obtained: the deformation of the roof subsidence and lower rib closure of the bottom gas extraction roadway are larger than the floor heave and upper rib closure, respectively. According to the mechanical analysis of the bottom gas extraction roadway, the equations for calculating the displacement at each point on the surface of the bottom gas extraction roadway and the methods for calculating the maximum displacement, the maximum normal stress, and the maximum shear stress are obtained to reasonably explain the deformation of the bottom gas extraction roadway under multiple disturbances. Then, the bolt‐mesh‐anchor and ladder beam support mode are designed. After onsite observation of the bottom gas extraction roadway of the 12030 coal mining face of the Pingbao Coal Mine, it is concluded that the deformation characteristics of the bottom gas extraction roadway basically conform to the abovementioned equations and that the support is effective. This paper can provide a reference for the optimization of bottom gas extraction roadway positioning, the determination of support parameters, and the deformation prediction around a bottom gas extraction roadway under similar conditions.
Highlights
At present, there are two main measures to prevent outburst at coal mining faces: one is to exploit protective seams and the other is to predrain coal seam gas [1]
For mines without protective seams to mine, the predraining coal seam gas is generally used as the main means of regional outburst prevention. e main principle of this method is that after the completion of the construction of the bottom gas extraction roadway, a certain number of extraction holes are drilled from the roof of the bottom gas extraction roadway to predrain gas from the overlying coal seam [2, 3]
In the process of coal roadway excavation and working face mining, the bottom gas extraction roadway is disturbed repeatedly, which destroys the structure and stability of the roadway surrounding rock and causes the bolts and anchor cables to undergo changes in their stress state or even fail; these effects are manifested as deformation, subsidence, and destruction of the bottom gas extraction roadway [4]. e deformation of the bottom gas extraction roadway is mainly related to the transfer of abutment pressure in the floor caused by coal seam disturbance. e deformation characteristics of bottom gas extraction roadways vary with the location of the roadway
Summary
There are two main measures to prevent outburst at coal mining faces: one is to exploit protective seams and the other is to predrain coal seam gas [1]. E peak stress to the upper rib of the bottom gas extraction roadway is 33.5 MPa, which is 7 MPa higher than that of the second disturbance, and the peak value occurs 2.45 m into the surrounding rock of the roadway. E distribution of the stress and plastic zone in the roof and floor and two ribs of the bottom gas extraction roadway under three disturbances, namely, excavation of the bottom gas extraction roadway, excavation of the coal roadway, and mining of the coal face, are determined through simulation. E peak value of the vertical stress to the upper rib of the bottom gas extraction roadway first decreases and increases, mainly due to the pressure relief of the floor after coal seam mining. After the roof coal seam is mined, the pressure relief is sufficient and the peak value of the horizonal stress to the roof of the bottom gas extraction roadway
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