Analysis on deformation characteristics of surrounding rock of gob-side entry retaining with soft bottom in thick coal seam and strengthening support technology of roof and side

The deformation and failure mechanism of surrounding rock and the control measures under the condition of long-time high superimposed stress are the keys to gob-side entry retaining support technology in thick coal seam with soft bottom. The existing research on the deformation and failure mechanism of surrounding rock and support control of gob-side entry retaining in thick coal seam is mainly aimed at deformation of roof and side of gob-side entry with hard rock bottom, and the strength of filling body and material proportion. There are few research on retaining roadway with soft bottom in thick coal seam. The mechanical analysis of gob-side entry retaining is incomplete, and the support scheme is single. In order to solve the above problems, taking N1303 working face of Gucheng Coal Mine of Shanxi Lu'an Chemical Industry Group Co., Ltd. as the engineering background, the failure mechanics models of roof, coal wall and floor are established. The deformation and failure characteristics of the roadway surrounding rock are analyzed. The roof is in a mixed stress environment, which is prone to tensile failure. Under the action of high stress, the solid coal side suffers compression shear failure, and the anchor rod fails. The filling body intrudes into the floor under pressure, causing the floor to tilt and lose stability, which is prone to soft coal broken and swelling. According to the deformation and failure characteristics of surrounding rock, the trinity surrounding rock support control scheme is proposed, namely, controlling the roof, restricting the coal side and yielding floor. In order to ensure that the roof can balance the stress distribution above the gob-side entry retaining, the method of anchor cable + filling body top cutting is adopted. Thus the roof does not form a cantilever beam structure above the roadway, only sinking occurs, and there is no rotary deformation. Considering the roof stability of gob-side entry retaining, the way of grouting anchor cable is adopted to grout the broken roof of the roadway to form a whole for better controlling the roof. In order to improve the support strength of the solid coal side, short anchor cables are added to connect the coal seam in the limit equilibrium area with the deep elastic bearing layer, and reduce the support resistance of the filling body beside the roadway. The proper yielding of the floor is beneficial to the flexible support of the whole roadway. The floor is reinforced by digging grooves and pouring strip foundations under the filling body wall. The original gob-side entry retaining support scheme is optimized by using the trinity surrounding rock support control scheme. The field test results show that after using the optimized support scheme, the roof movement subsidence is reduced from 337 mm to 142 mm, and the coal side movement is reduced from 305 mm to 70 mm. The floor movement is reduced from 675 mm to 162 mm, and the roadway convergence rate is reduced from 34.1% to 10.73%. The working resistance of the anchor rod (cable) is stable, the filling body is free of damage and inclination, and the support effect is good.