Research and application of schemes for constructing concrete pillars in large section finishing cut in backfill coal mining

Based on the technology of controlling surrounding rock deformation by constructing concrete pillars in large section finishing cut in backfill coal mining, the characteristics of vertical stress on concrete pillars and main factors influencing pillar stability are analyzed. By building a Winkler elastic foundation mechanical model for the support system constituted of coal pillar, backfill body and concrete pillars, mechanical calculation on stability of concrete pillar is carried out to evaluate the pillar stability and safety. Seven numeral models in three schemes with different pillar sizes, inter-row distances and compression ratios at the stopes were analyzed through numerical simulation according to width reduction principle. The practice of finishing cut at III644 workface at Yangzhuang coal mine shows that: when the actual compression ratio is 86.5%, construction size inside the finishing cut is 2000 mm × 2000 mm and the interval between concrete pillars is 2000 mm × 2000 mm, the pillars can be stable with the maximum movement of two sides of each pillar being only 83 mm and 54 mm, which achieves the expected effect.