Roof Fracture Instability Mechanism And Control Study Of Thick Coal Seams Mining For Super Thick And Hard Rock In Close Distance

With rich reserves of coal resources of thick and hard rock(THR)occurrence in close distance in China,the working face strong ground pressure appears easily due to the overlying strata fracture instability under this condition,affecting the safe production of the working face.Therefore,it is urgently needed to set a systematic study of the overlying strata activity law,its instability mechanism,and their control.Taking the thick coal seams fully mechanized caving of THR occurrence in close distance of the Zhuxianzhuang Coal Mine as the engineering background,the thesis systematically studies the physical mechanical characteristics,fracture characteristics,collapse migration law,roof structural characteristics and the support-surrounding rock interaction characteristics of THR with a combination of site investigation,theoretical analysis,physical simulation and numerical simulation,proposing the regional roof cooperative control method and technology based on the THR pre-control.The thesis has achieved the following results:(1)Based on the establishment of the thick-plate mechanical model for THR fracture occurrence in close distance,the study reveals the fracture instability characteristics and collapse migration law of “whole fracture” and “whole collapse” of THR occurrence in close distance under the condition of large scale mining space,thus obtaining the mechanical conditions of its fracture instability.The working face is divided into several regions with different ground pressure strength according to the various roof occurrence conditions,identifying the roof conditions and mining areas where strong ground pressure appears easily.(2)The thesis studies the displacement variation rule,stress field evolution law and energy dissipation mechanism of thick and hard rocks,investigates the influence law of rock thickness,mining scale and immediate roof thickness on the stability of thick and hard rocks,and puts forward the instability criterion and control principles based on the energy theory.(3)On the basis of immediate roof thickness variation,the thesis establishes a mechanical model for the interaction between super thick and hard rock(STHR)and support,analyzes the interaction relation characteristics of STHR occurrence in close distance and support,and derives the calculation formula of the working resistance of support under this condition.(4)Combining the STHR occurrence conditions in close distance of the Zhuxianzhuang Coal Mine,a method and technology for the regional roof cooperative control based on the pre-control of thick and hard rocks are proposed.With support rational selection as the center,a roof cooperative control system on the premise of THR deep-hole confined the blasting weakening pre-control is established,which provides guarantee for the safe and highly-efficient mining of thick coal seams under STHR occurrence in close distance.