Study on Coal Pillar Width and Surrounding Rock Control of Gob-Side Entry in Extra-thick Coal Seam

This paper adopts an integrated method of field test and numerical simulation to study coal pillar width and surrounding rock control of gob-side entry in extra-thick coal seam. Field test showed that when the coal pillar width was 30 m, the average plastic failure areas of the roof, coal pillar rib and virgin coal rib were 7.6 m, 4.9 and 3.8 m, respectively, and severe roof subsidence and large deformation of coal pillar rib occurred during the mining of the working face. A numerical model is established to study the change of plastic bearing zone and the distribution of stress and displacement under different pillar widths. The numerical results show that a coal pillar 8 m wide can meet the strength requirement of overlying load and puts the gob-side entry in a good stress environment. Finally, an optimal coal pillar width was estimated at 8 m and an effective support method was proposed. Drilling imaging data indicate that the newly designed pillar size and the proposed supporting method can ensure roadway stability. The proposed plastic bearing zone and zero-displacement plane are reliable indicators for designing pillar size. In addition, the new support strategy can be applied to other coal mines with similar geological conditions.