Mechanical analysis of floor deformation and floor heave control technology for gob-side entry retaining in medium thick coal seam with shallow cover depth

Gob-side entry retaining technology is of great significance to improve coal recovery rate, improve roadway stress environment and ensure mine safety and efficiency. In order to solve the problem of floor heave deformation of gob-side entry retaining in shallow coal seam, based on the engineering background of 12407 and 12408 fully mechanized mining face in Wulanmulun Coal Mine, the concept of equivalent load is introduced based on the roof load strip segmentation method, and the equivalent load distribution model of gob-side entry retaining floor is established. The mechanical analysis of gob-side entry retaining floor is carried out and the maximum floor heave of roadway floor is calculated. FLAC^3D numerical calculation method is used to analyze the main control factors of floor heave deformation of gob-side entry retaining. The numerical simulation results show that the strength difference between roadside filling body and isolated coal pillar leads to asymmetric deformation of roadway floor, and under the combined action of advanced high stress and high strength support. The floor becomes the weak link in the bearing system of surrounding rock and finally fails. Based on the above theoretical analysis, numerical simulation and field engineering practice, the floor heave control technology of gob-side entry retaining in shallow coal seam is proposed. The conclusions indicate that the serious floor heave of gob-side entry retaining is mainly due to the high stress shear failure and tensile failure of the floor strata caused by the high stress of the coal body in the plastic zone of the advance section and the roadside support body after the working face advancing. By optimizing the support scheme, the roof can be prevented from falling in time after the working face is advanced, which can effectively reduce the deformation of the floor heave of the retaining roadway. The design of the filling body at the mountain corner is proposed, and the matching of the filling body parameters and the strength of the floor rock layer is optimized. The prevention and control measures of the floor heave of the gob-side entry retaining are to control the floor heave of the gob-side entry retaining from three aspects : reducing the stress concentration in the high stress area, alleviating the pressure relief deformation of the roadway floor and improving the strength of the floor rock layer. The field engineering practice shows that the above method has a good improvement on the floor heave effect of the gob-side entry retaining, ensures the safety of the gob-side entry retaining, and realizes the safe and economic mining of the mine without coal pillar.