Cooperative control of face wall stability and top-coal cavability of LTCC panel in hard seam with large cutting height and hard roof

ully-mechanized top-coal caving with large-cutting-height (LC-HTCC) is a key technology for the safe and efficient mining of ultra-thick coal seams. However, the exceptionally large mining space intensifies the inherent contradiction between wall stability and the cavability of hard top coal. This conflict becomes particularly acute when both the coal seam and the immediate roof are highly competent, significantly limiting the potential for achieving super-high production rates. Taking Panel 111 of the Jinjitan coal mine as a case study, theoretical analysis, laboratory testing, numerical simulation and in-situ monitoring were performed to investigate the coupled failure mechanism of the high rib and hard top coal under these challenging geological conditions. A structural model of the support–surrounding rock system is established, and analytical expressions for support resistance and rib pressure under massive hard-roof impact are derived, demonstrating that support stiffness governs load transfer within the roof. By applying the principle of minimum potential energy, the ultimate bearing capacities of the high rib and hard top coal are determined, and the conditions for coupled instability, cooperative stability and asynchronous response are clarified. Stability and cavability indices are defined and found to change with the cutting-to-caving ratio according to a negative exponential law, quantitatively characterizing the negative feedback between rib stability and top-coal cavability. A synergistic control strategy was developed, incorporating massive hard-roof fracturing, high-strength/high-stiffness support, optimization of the cutting-to-caving ratio, and face layout redesign. Field implementation resulted in a 60% reduction in rib damage and a top-coal recovery rate of 83%, enabling the safe and efficient extraction of an ultra-thick coal seam using the LC-HTCC method.