Roof cutting mechanism and surrounding rock control of small pillar along-gob roadway driving in super high coal seam

In view of the low recovery rate associated with wide coal pillar and the strong strata behavior associated with small coal pillar, the roof cutting pressure relief of small pillar in super high coal seam in along-gob roadway driving is examined in the context of Yongdingzhuang Coal Company through field measurement, theoretical analysis, numerical simulation, and field test. The following findings are obtained: (1) the strong strata behavior of along-gob roadways arises in response to the presence of a high stress zone near the coal pillar due to large mining thickness, small immediate roof thickness, large main roof hardness, large rotating space, and the 7.8-m distance of the main roof fracture from the gob-side coal wall; (2) after roof cutting, L2 < L1, the main roof caving length is reduced to some extent; (3) during hydraulic fracturing, when the main fracture encounters a 90° preexisting fracture, it will deflect and propagate in an approximate bidirectional symmetry, but when it encounters a 45° preexisting fracture, it will propagate in a unidirectional asymmetry; (4) different roof cutting parameters are simulated by 3DEC, a precise hydraulic roof fracturing scheme is designed. A supporting technique cored around “reinforcing bolt (cable) + strong W strip” is proposed, and applied it to the engineering project, realizing stability in the test section roadway; thus, the study provides a reference for surrounding rock control of small pillar along-gob roadways.