Shear sliding block movement mechanism and cooperative control technology for coal pillar in soft and thick coal seam

Coal pillars in soft and thick coal seam are often tall and have large exposed coal walls, and the coal quality is soft with some developed cracks, which can easily cause an instability of coal pillars and make roadway maintenance difficult. This paper takes the No. 3 coal seam in the Fuyan Coal as the engineering background, based on the shear sliding block theory, explores the mechanism of coal pillar deformation and failure under mining influence, analyzes the width of the coal pillar’s limit equilibrium zone and stress distribution rules, and reveals the movement mechanism of the coal pillar’s shear sliding block. Based on this, the cooperative control strategies for coal pillar stability are proposed and verified through engineering practice. The results show that: ① by using the limit equilibrium theory and the superposition theory, the range of shear sliding block movement of the coal pillar and the vertical stress distribution law of the coal pillar are determined, and the distribution law of the safety factor of the coal pillar shear sliding block is clarified. The safety factor of the upper part of the coal pillar is small at a depth of 0−1.26 m. In the area of 1.26−3.95 m, the central part of the coal pillar has a large area of small safety factor and is vulnerable to damage from the roof. ② A cooperative control technology for coal pillar is proposed, which is based on “reinforcement anchor cable-grouting reinforcement-advance cutting roof”, and it effectively controls the deformation and bottom bulging of the coal pillar. The side cracks of the coal pillar without supporting conditions and those with original supporting conditions are reduced by 62.89% and 46.26%, respectively. The integrity of the surrounding rock of the roadway is greatly improved, forming a strong bearing structure. ③ According to the conditions of coal pillar in the thick and soft coal seam section, the design parameters of coordinated control are reasonably determined, and the prevention and control effect of coal pillar is evaluated by test monitoring. The field test results show that the cracks in coal pillar are fully filled, and the strength of coal body is increased by more than 63% after grouting. The roadway displacement, anchor cable stress, and separation layer are all within the controllable range, indicating that the cooperative control technology significantly improves the bearing capacity of the coal pillar, and effectively controls the deformation of the surrounding rock of the mine roadway, providing space guarantee for safe and efficient mining.