Structure coupling between hydraulic roof support and surrounding rock in extra-thick and hard coal seam with super large cutting height and longwall top coal caving operation

Aimed at the challenges,such as long overhanging top-coal,poor cavability,low recovery and incoordination of coal cutting and coal drawing,faced in longwall top coal caving (LTCC) mining with extra-thick and hard coal seam in Yushen mining area,the authors discussed the feasibility and necessity of LTCC operation with super-large cutting height (greater than 6. 0 m),and analyzed the coupling between hydraulic roof support and surrounding rock. Based on the coupling of strength,stiffness and stability of support-surrounding rock,a structure coupling theory of support- surrounding rock in LTCC mining with super-large mining height is put forward. The concepts and theories of “ small structure” primary coupling,active supporting,and “large structure” secondary coupling,passive bearing,in the sup- port system of hydraulic supports and the surrounding rock are explained from the perspective of the interaction mecha- nism between them. The authors analyzed the influence of “large and small structure” coupling of surrounding rock on the supporting effect and adaptability. It is pointed out that the structural design of hydraulic support used in LTCC not only needs to meet the requirement of adaptation of small structure supporting system to the strong dynamic load caused by periodic failure and instability of large structure,but also needs to consider the influence of the structure of hydraulic support (especially the structure of coal drawing mechanism) on the caving and migration law of hard top- coal,as well as the load evolution process of the support. The coupling between the structure of hydraulic support and the structure of caved top-coal can realize a smooth drawing of top coal and improve the recovery rate of top-coal. The methods of theoretical analysis,similarity simulation,numerical simulation and field investigation are adopted to ana- lyze the caving and drawing structure of hard top coal and the arching effect during the coal drawing process. The in- fluence of the structure height of hydraulic support on the caving structure and resource recovery rate of the top coal is discussed. The effect of caving mechanism structure on the arch structure of top coal and the secondary crushing effect of caving mechanism structure on top coal are studied. The structural improvement and optimization strategies of the strong coal drawing mechanism are put forward,and the mechanism and effect of coal breaking are discussed. This pa- per would provide guidance and reference for the coupling theory of hydraulic roof support and surrounding rock in similar hard and extremely thick coal seam.