Experimental Study On Fracture Behavior Of Stope Roof Based On Acoustic Emission Technology

In the coal mining process, quasi-periodic fracture of working face roof appears, so the roof is a typical system with variable boundaries(SVB). Because the fracture position is unknown in advance and the connectivity of roof configuration after fracture is completely different from that at initial moment, fracture behavior of stope roof in the coal mining process is beyond the research scope of traditional solid mechanics. The fracture process is accompanied with acoustic emission activities, and acoustic emission technique is an effective means to explore fracture behavior of stope roof.Because SVB generally exists in mining engineering, urgent requirements have been pressed to SVB research for the purpose of environmental protection and mine disaster prevention and control. Through physical simulation, this paper studies the breaking process of stope roofs, employs the acoustic emission technology to determine the location of fracture sections and fracture time, and makes in-depth study of the fracture law of stope roofs. Through research, the following innovative achievements have been made:(1) Through the rock acoustic emission test, this paper acquires the influential laws of stiffness of test machine and loading rate on the parameters of acoustic emission signals.(2) On the basis of analyzing the constraint conditions, force conditions, boundary variation characteristics and fracture process of stope roofs, this paper designs a set of acoustic emission testing systems for variable boundary in strata fracture, which provides experiment means for investigating roof boundary time-dependent fracture behavior.(3) The method to relieve constraints is employed to realize roof boundary changes. In addition, the pressure changing factor is introduced to characterize the constraint release range of the roof bottom. The relationship between roof fracture position, fracture time and pressure changing factor has been established and also the influential laws for stress of primary coal rock on the formation time of fracture sections, separation distance between fracture sections and the release of energy have been obtained.(4) By conducting acoustic emission experiments of the roof fracture process under different loading conditions, this paper applies the acoustic emission diagnostic imaging technique to analyze the fracture way of roof strata, and thus obtains the law of roof strata converting from brittle fracture to ductile fracture.(5) The diagnostic imaging technology is used for the analysis of acoustic emission signal parameters. Besides, this paper presents the diagnostic imaging method for acoustic emission positioning of the fracture sections of roof strata.(6) By carrying out a diagnostic imaging experiment with acoustic emission positioning of the roof strata, this paper accurately determines each of the fracture sections and fracture time for the variable boundary rocks.