Research On Mesoscopic Mechanism Of Rock Failure And Acoustic Emission Precursor Characterization Of Failure And Instability

The failure process and mechanism of rock is always the one of hotspot and difficulty in rock mechanics and other subjects. Rock macroscopic failure is closely related to the internal mesoscopic structure and defects. To investigate the rock instability mechanism, the production, expansion and failure process of internal microcracks of rock must be studied from the rock failure mesoscopic point of view. Direct dynamic observation of rock internal microcracks is difficult; AE method become the effective tool to study the dynamic process of microcracks in rock deformation and failure process. However, because of the lack of essential cognition about the AE mechanism and the relationship with rock failure, the research on the rock internal microcracks with AE technology primarily relied on conjecture. Consequently, carrying out a research on the mesoscopic mechanism of rock failure, studying the relationship between AE and mesoscopic damage, has important theoretical and practical significance to understanding the rock failure mechanism and applying the AE technology into the monitoring and prediction of rock failure instability.Using the real-time loading and CT scanning method, the development law of rock internal microcracks at different stages before the peak load and the relationship with acoustic emission is be studied, using the non-real-time loading CT scanning method, the occurrence characteristics of rock internal transfixion crack after the peak load and the relationship with acoustic emission is be studied, Then the rock failure mechanism and AE event mechanism is revealed, the relationship between the acoustic emission and rock failure is established, With AE technology, the failure process of large scale samples is studied, the AE characteristics of failure instability precursory are put forward. Finally, with the RFPA numerical analysis software, from failure process and stress distribution point of view, explore the three-dimensional space law and failure mechanism of crack propagation in rock failure process. The main research work is summarized as the following respects:(1)The loading device supporting the CT system and AE measurement and analysis system is manufactured, real-time loading CT scanning and AE real-time acquisition simultaneously is realized in action. Using this experimental system, variation laws and AE characteristics of internal native cracks and porosity of mudstone and sandstone samples before peak load in the loading process at different loading stages are observed. The microcrack initiation, propagation law and particle role in the process of crack propagation is studied, the relationship between the failure modes of surface cracks and rock internal mesoscopic structure is analyzed, the cause of AE events and the relationship between AE temporal and spatial distribution characteristics and mesoscopic failure is analyzed, the relationship between AE energy and the type of mesoscopic failure is established.(2)Using the non-real-time loading CT scanning method, occurrence characteristics and AE temporal and spatial distribution characteristics of internal transfixion crack of granite and gabbro after peak load are analyzed, the failure crack initiation, propagation law and the effect of particle in the process of crack propagation is studied. The propagation of rock internal transfixion crack is analyzed, the relationship between AE spatial distribution characteristics and mesoscopic failure and transfixion crack propagation is studied, the relationship between AE ringing counting and crack width is established.(3)Using AE technology, the AE characteristics of failure process and the instability precursory of fine sandstone. granite and gabbro are studied. According to AE temporal and spatial distribution characteristics, combining with the ultimate rock failure case, the paper put forward the AE accumulation cluster area characteristic is the first precursory of rock failure and instability and AE accumulation blank region characteristic is the second precursory, then failure and instability can be predicted in turn.(4)Using RFPA2D software, the effect of heterogeneity on failure process and mechanism is studied, the process of mesoscopic microcrack initiation, propagation and transfixion and the mechanism of macroscopic crack transfixion and propagation is studied. Using RFPA3D software, the process of microcrack initiation, propagation and transfixion and the mutual effect between macroscopic cracks is analyzed from stress field evolution and three-dimensional space extension point of view.