Stress transfer law and control of roof cutting in entry with extremely narrow coal pillar in extra-thick top-coal caving conditions

To solve the problems of high stress, large deformation, and difficult control in the entry with extremely narrow coal pillar in extra-thick top-coal caving conditions, the relationship between the support force of the extremely narrow coal pillar and the roof-cutting length and angle was analyzed, the stress distribution characteristics and deformation evolution laws of the roof and coal pillar under different roof-cutting schemes were comparatively analyzed, and a coordinated "cutting-support-grouting" control technology was proposed. The analysis results showed that after roof cutting and pressure relief were implemented in the gob-side entry in extra-thick top-coal caving conditions, the support force of the extremely narrow coal pillar gradually decreased with increasing roof-cutting length and inclination angle, and the decreasing extent gradually increased. Increasing the roof-cutting length and angle caused both the vertical stress at different heights from the floor and the positions of the vertical stress intersection points in the coal pillar to move toward the entry, which was conducive to the stability management and control of the coal pillar. Field application results showed that after the coordinated control technology was adopted, the maximum displacement of the entry with extremely narrow coal pillar was only 269.03 mm, the maximum displacements of the surrounding rock on the coal-pillar side and the solid-coal side were 220.18 mm and 195.36 mm, respectively, and the minimum displacement of the floor of the entry was 92.83 mm. The surrounding rock deformation was effectively controlled, the cross-sectional area was ensured, and the entry shape could meet the service requirements.