Study on roadway roof deformation and coal pillar energy accumulation instability

To address coal pillar instability, the study focuses on the 3-1 coal seam coal pillar at Nanliang Coal Mine. It analyzes the bending deformation energy of the main roof and the pre-yield elastic energy of the coal pillar's elastic zone through theoretical analysis, similar simulation, and field measurements. The formula for the bending elastic energy of the main roof is derived by establishing the mechanical model of the roadway's main roof near the goaf side. Based on the side abutment stress distribution of the coal pillar, the calculation of the pre-yield elastic energy distribution along the width direction of the coal pillar's elastic zone is conducted, leading to the derivation of the instability energy criterion for the coal pillar. The range analysis method is used to analyze the influencing factors and distribution patterns of the bending elastic energy of the main roof and the pre-yield elastic energy of the coal pillar's elastic zone. Findings indicate that the main roof's tensile strength is the primary factor influencing bending elastic energy. Higher tensile strength of the main roof, and smaller load, larger thickness and elastic modulus on the overlying strata, lead to higher bending elastic energy in the main roof. The internal friction angle, width of the coal pillar, and elastic modulus of the coal seam notably impact the pre-yield elastic energy of the coal pillar's elastic zone. A larger internal friction angle and coal pillar width, along with a smaller elastic modulus, result in higher pre-yield elastic energy in the coal pillar's elastic zone. Using the working face of 3-1 coal seam in Nanliang Coal Mine as the engineering context, the study calculates the minimum coal pillar width required for stability. Physical simulations and field monitoring demonstrate that with a 9 m-wide coal pillar, there is no apparent deformation or failure in the surrounding rock of the roadway, indicating good internal rock stability.