Coal wall stability and top-coal failure mechanisms under thick and hard roof conditions in a fully mechanized top-coal caving face: a case study

Abstract

Fully mechanized top-coal caving mining in extra-thick coal seams under thick and hard roof conditions is often accompanied by prominent problems such as severe coal wall spalling, insufficient top-coal fragmentation, delayed caving, large-area hanging roof, and strong ground pressure behavior. The coupling relationship between coal wall stability and top-coal caving performance is still unclear. Taking the 12,112 working face in northern Shaanxi mining area as the engineering background, this study establishes a cantilever beam model of thick and hard roof and a load-bearing rod model of coal wall to reveal the load transfer law and the critical bearing capacity of coal wall. The evolution characteristics of overburden displacement field and coal stress field are analyzed by numerical simulation. The results show that the load on the composite bearing structure is positively correlated with roof thickness and cantilever length, and the critical bearing load of coal wall is inversely proportional to coal wall height. Under the original cutting–caving ratio of 1:0.5, violent initial weighting causes serious coal wall spalling. By comparing four groups of schemes, the optimal cutting–caving ratio is determined to be 1:0.8, which can significantly improve coal wall stability and ensure good top-coal caving effect. The research results provide a theoretical basis for safe and efficient mining of fully mechanized top-coal caving face under similar thick and hard roof conditions.