Abstract
In order to solve the problems of stress concentration and large deformation of surrounding rock of secondary gob-side entry retaining in thin coal seam caused by hard overhanging roof, the method of cutting off overhanging roof on both sides of roadway by manual pre-cutting seam is adopted. It can transfer high stress to goaf on both sides of roadway and reduce roadway deformation. The mechanism of roadway formation, the conditions of double side overhanging roof subsidence and the stress reduction of roadway side support of secondary gob-side entry retaining after double side roof cutting are given. This paper studies the pressure relief law of secondary gob side entry retaining after double side roof cutting in thin coal seam. After double side roof cutting, the stress of roadway side support is reduced by 76%, the maximum vertical displacement of roof is reduced by 84%, and high stress is transferred to goaf. The influence of different double side roof cutting thickness and angle on the pressure relief effect is analyzed. On the premise that the collapsed gangue can fill the goaf, the smaller the thickness of double side roof cutting is, the better the pressure relief effect is, and the greater the double side roof cutting angle is, the better the pressure relief effect is. It has been successfully applied in the left five roadway of No. 69 coal seam in Xinqiang coal mine, and the deformation of roof and floor is reduced by 47% and the deformation of two sides is reduced by 56% after double side roof cutting. It has important reference value for the future secondary gob-side entry retaining.
Highlights
The secondary gob-side entry retaining refers to retaining the gob-side entry again after reusing gob-side entry
The secondary gob side entry retaining can be used as a return air roadway in the mining face of the adjacent coal seam, which has a significant effect on gas control in the adjacent coal seam
The results show that the structure and stress distribution of surrounding rock of roadway are optimized by using double side roof cutting and pressure relief, which can effectively reduce the influence of double side overhanging roof structure and mining stress on roadway, transfer high stress to goaf, and improve roadway stability
Summary
The secondary gob-side entry retaining refers to retaining the gob-side entry again after reusing gob-side entry. Left five roadway of No 69 coal seam in Xinqiang coal mine as the research background, based on the stage deformation law of surrounding rock of secondary gob-side entry retaining without roof cutting, the conditions of double side overhanging roof subsidence and the stress reduction of roadway side support are given. As shown in the F-F section, after the second mining face is mined for a certain distance, the movement of the main roof over the roadway is gradually gentle, the stress redistribution is basically completed, and the surrounding rock deformation is reduced. Considering the overall stability of the roadway, the secondary gob-side entry retaining with double side roof cutting is only applicable to thin coal seam; and the reused secondary gob-side entry retaining is only used as a return air roadway of the corresponding mining face in the adjacent coal seam to control the gas and prohibit personnel from entering
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