Roof-cutting pressure-relief effects and surrounding rock control technology for narrow-pillar gob-side entry driving in extra-thick coal seams with hard roofs

During fully mechanized top-coal caving in an extra-thick coal seam under a hard roof, suspended structures formed by multiple hard strata generate concentrated loads. Together with plastic failure of a narrow coal pillar, these loads exacerbate gob-side entry deformation. Key-strata identification, numerical simulation, and field monitoring were used to examine how coal-pillar width and roof-cutting height affect stress distribution in the 1521 return airway at Chaigou Coal Mine. The results are as follows: (1) A 10 m coal pillar places the entry in a relatively low-stress zone on the gob side of the lateral abutment-pressure concentration zone. (2) Roof cutting to heights of 30 and 100 m reduces the peak lateral abutment pressure by 9.6% and 35.2%, respectively. The corresponding reductions in the integral of the lateral abutment-pressure increment are 4.9% and 49.1%. Low-level roof cutting to 30 m primarily reduces local stress concentration and promotes stress redistribution deeper into the solid coal. At a roof-cutting height of 100 m, roof cutting encompasses intermediate- and high-level key strata and produces greater pressure relief. The additional stress reduction occurs mainly in the solid-coal rib, whereas the mean stress in the coal-pillar rib changes only slightly. (3) The field control scheme combined hydraulic fracturing of high- and low-level roof strata with high-pretension bolt-and-cable support and grouting reinforcement. Following its implementation, the maximum rib-to-rib and roof-to-floor convergence values during mining were 643 mm and 314 mm, respectively. No anchorage failure or abrupt load drop was observed in the cable bolts in either rib. These findings indicate that the combined control scheme can effectively reduce lateral abutment-pressure concentration and improve the stress environment of the gob-side entry while maintaining the load-bearing function of the support system.