Sustainability, Vol. 9, Pages 2079: Analysis and Optimization of Entry Stability in Underground Longwall Mining (Sustainability)

For sustainable utilization of limited coal resources, it is important to increase the coal recovery rate and reduce mine accidents, especially those occurring in the item (gateroad). Entry stabilities are vital for ventilation, transportation and other essential services in underground coal mining. In the present study, a finite difference model was built to investigate stress evolutions around the item, and true triaxial tests were carried out at the laboratory to explore item wall stabilities under different mining conditions. The modeling and experimental results indicated that a wide coal pillar was favorable for item stabilities, but oversize pillars caused a serious waste of coal resources. As the width of the item wall decreased, the integrated vertical stress, induced by two adjacent mining panels, coupled with each other and experienced an increase on the item wall, which inevitably weakened the stability of the item. Therefore, mining with coal pillars always involves a tradeoff between economy and safety. To address this problem, an innovative non-pillar mining technique by optimizing the item surrounding structures was proposed. Numerical simulation showed that the deformation of the item roof decreased by approximately 66% after adopting the new approach, compared with that using the conventional mining method. Field monitoring indicated that the stress condition of the item was significantly improved and the average roof pressure decreased by appropriately 60.33% after adopting the new technique. This work provides an economical and effective approach to achieve sustainable exploitation of underground coal resources.