Energy-based indicators and optimization of coal pillar width in gob-side entry driving

Gob-side entry driving is widely applied in deep coal mines, where rapid unloading of surrounding rock on the gob side induces stress redistribution, and the coal pillar is consequently regarded as a key load-bearing structure. The stability of the roadway is governed by the competition between elastic elastic strain energy and dissipated energy within the coal pillar. To address the difficulty of identifying stability state transition points in coal pillar width design under deep burial and weak rock conditions, this study analyzes the surrounding rock response from an energy perspective and establishes an energy analysis framework based on the coupling of elastic elastic strain energy and dissipated energy, with the dissipated energy ratio introduced as an evaluation index. Based on FLAC3D numerical simulations, the spatial distribution and evolution of elastic strain energy, dissipated energy, and dissipated energy ratio under different coal pillar widths are investigated. The results indicate that when the coal pillar width increases from 4 to 6 m, the bearing mechanism gradually shifts from plastic dissipation-dominated behavior to an elastoplastic coordinated state dominated by elastic elastic strain energy, with the dissipated energy ratio decreasing from 1 to approximately 0.67. When the width further increases to 8 ~ 14 m, elastic strain energy rapidly accumulates in the central region of the coal pillar, resulting in the formation of a pronounced energy concentration zone. Compared with traditional indicators based on stress, displacement, and plastic zone distribution, the dissipated energy ratio is more effective in characterizing. Considering energy evolution characteristics, bearing capacity, and engineering economy, a 6 m coal pillar is considered to achieve the most favorable balance under the conditions of the studied mine. Field monitoring results further verify the engineering applicability of the proposed energy-based criterion and coal pillar width optimization scheme.