Space-time relationship between the first fracture of main roof structure and whole regional rebound

In order to study the space-time relationship between the first fracture of main roof structure and the whole regional rebound compression field,a mechanics model for the first fracture disturbance of main roof plate structure with elastic foundation boundary was established. Based on the finite difference theory and the fracture criterion of pri- mary moment,the basic morphology characteristics of the whole regional rebound compression field formed in the first fracture of main roof structure were studied. Furthermore,the effects of fracture length,fracture development process and fracture degree of main roof on the whole regional rebound compression field were also studied. The following con- clusions were obtained after those studies:① When the fracture of main roof arises ahead of the surface of coal body,“semi-ellipse rebound zone I”,“ elliptical ring compression zone”,“ elliptical ring rebound zone II” and “ elliptical ring compression zone” are successively generated at the periphery of the fracture line. ② The rebound volume in the middle part of rebound zone I in front of the fracture line is the largest,and the compression zone is at both ends of the fracture line. ③ When the first fracture length and the second fracture length are smaller,“M-type rebound zone I”, “ elliptical ring compression zone” and “elliptical ring rebound zone II” are successively generated at the periphery of the fracture line. However,when the first fracture length and the second fracture length are larger,“ M-type rebound zone I”,“ring 8-shape compression zone” and “ring 8-shape rebound zone II” are successively generated at the pe- riphery of the fracture line. ④ The bigger the fracture degree of main roof is,the greater the rebound volume will be, but the partition features of rebound compression zone are independent of the fracture degree. ⑤ The rebound zone II has encircled the entire “hanging roof area” with running through the two roadway areas and adjacent roadway area. Moreover,the vertical distance from the inner boundary line to the outer boundary line in rebound zone II is basically equal. Consequently,the rebound compression information can be detected in the two roadway areas and adjacent road- way area when the fracture of main roof arises ahead of the surface of coal body. The rationality of the conclusions has been verified by engineering practice and the experiment adopting the custom-built high-accuracy displacement sen- sor. The principle of “one synchronization and two delays” and the monitoring position and method of “two zones and two indexes” for the early warning of first fracture of main roof with large area are formed.