| Fractured rock mass is a complex geological condition in underground engineering,the local stress concentration of rock mass will inevitably cause geologic body to crack initiation,slip,deformation and even lose stability.It is easy to lead to the occurrence of rock burst,slope instability,tunnel collapse and other disasters.Therefore,studying the law of rock crack propagation and fracture,even grasping the precursory signal characteristics of rock failure by acoustic emission is of significant guiding for underground engineering.In this paper,studyed the crack propagation characteristics on the time and space fracture process of rock-like with or without prefabricated cracks through theoretical analysis,laboratory research and numerical simulation,obtained the characteristics of acoustic emission precursor signals that were damaged and unstable,the research results can be used to provide reference for the analysis of coal mine safety and underground engineering stability.1)In this paper,the mechanical characteristics of crack tip,the propagation model of micro cracks and the propagation criterion of crack surface under stress action were summarized and analyzed.A new type of rock-like which satisfied the basic mechanical properties of brittle and ductility was prepared through the theory,and the stress-strain curves and failure characteristics of the single axial compression test were verified by the PFC numerical model,the results of the test were in good agreement with the model results.2)The crack propagation and fracture characteristics of the complete rock-like with different intermediate principal stresses were analyzed based on the true true triaxial test,and the influence of the intermediate principal stress on the crack propagation path was obtained,which showed that the square angle between crack propagation direction and the maximum principal stress decreased,and the specimen was changed from the shear failure to pulling failure with the increase of the intermediate principal stress.The morphology of fracture surface was analyzed by scanning electron microscope,and the fractured surface,intergranular and microporous aggregation fracture within the tensile and shear stress were obtained.The acoustic emission detection system was used to collect the crack fracture acoustic signal,and the fracture characteristics of the rock-like were analyzed.The precursory information of acoustic AE after energy accumulated of damaging specimen can provide references for rock failure and rock mass instability.3)Through the compression test of a double presupposed fractured rock specimen with free surface,the influence of the length of the fracture,the length of the rock bridge and the free surface on the law of the fracture expansion and evolution was studied and analyzed.The crack propagation characteristics and the penetration mode of the crack under the two-way stress collapse and the different distribution position of the double fissure were analyzed.The initiation,propagation and penetration process of the crack in double cracks were reproduced with the PFC numerical analysis software,and the crack generation range of type Ⅰ,type Ⅱ and type Ⅲ was determined.The intermittent sound signals produced by the compaction of the primary fissure,the stable sound signals produced by the crack propagation in the crack tip,the one-time abrupt sound signals produced by the crack growth and evolution caused by the presupposed opening crack,the unstable sound produced by the micro fracture penetration and the two mutation sound produced that the macro crack was broken through the fracture were studied.The characteristics of the 5 stage AE signals in the process of crack propagation were obtained. |
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