Research on the stability and control technology of the surrounding rock in gob-side entry driving in an extrathick coal seam with varying thickness

The deformation and failure characteristics and control methods of the surrounding rock of a roadway have always been the focus of attention when gob-side entry driving (GED) is performed in extrathick coal seams. In this paper, field investigation, theoretical calculations and numerical simulations are performed to analyse the distribution range of the limit equilibrium area in the coal seam near the gob (CSNG) before GED and the stability of the surrounding rock after GED for different coal seam thicknesses. The research results are as follows: (1) If a 5 m coal pillar is planned for GED, the limit equilibrium area will gradually expand with increasing coal seam thickness. When the coal seam thickness exceeds 18 m, the driving position will be completely in the limit equilibrium area. (2) After GED, with the increase in coal seam thickness, the bearing capacity of the roadway roof and two sides gradually decreases, and the range of the plastic zone gradually expands. The roadway deformation changes from local deformation to large deformation, and the coal seam side and roof corner are the most affected areas. Based on these results and a new support technology called anchor cable with c-shaped tube (ACC), the surrounding rock control strategy and full-section ACC support scheme are proposed. The bidirectional control of the surrounding rock (in the axial and tangential directions) in the gob-side roadway of the extrathick coal seam is realized, as verified by numerical simulation and field application data.