Research On Rock Crack Identification Method Based On Acoustic Emission

Rock instability is caused by the gradual development of tension and shear fracture in rock mass.As an associated phenomenon of rock fracture,acoustic emission can describe the evolution process of tension shear fracture in rock through its parameter characteristics and waveform characteristics.Through the treatment of granite and marble rock specimens,indoor uniaxial loading test and shear test are carried out respectively to obtain the mechanical and acoustic emission parameters in the fracture process of the samples.Firstly,the acoustic emission characteristics of granite and marble under two different loading conditions are studied.Secondly,using the parameter analysis method proposed in JCMS-Ⅲ B5706,the crack classification modes of two types of rocks under uniaxial compression and direct shear loading are analyzed.Finally,most of the crack classification in acoustic emission parameter analysis comes from the empirical relationship between RA(Rise time/Amplitude)and AF(Average frequency)value,while the most important difference between shear crack and tension crack in parametric analysis the optimal dividing line has not been determined yet.A new method based on Gaussian Mixture Model(GMM)+ Support Vector Machine(SVM)algorithm is proposed to determine the optimal dividing line for crack classification in acoustic emission parameter analysis.Through the GMM+SVM hyperplane algorithm,the intersecting clusters between the tensile and shear crack regions can be accurately distinguished,and the SVM hyperplane boundary can be obtained.Granite and marble are dominated by tension cracks in the early and middle stages of the entire stress loading process,and the proportion of shear cracks in the later stage continues to increase.The proportion of shear cracks in granite has a sudden change in the stage of 80%～90%of the peak stress,while the proportion of shear-type cracks in marble has a sudden change in the stage of 70%～80% of the peak stress.Finally,it is verified that this method can correspond to different fracture modes of granite and marble during the entire stress loading process,and the proportion value can be used as an effective monitoring.Figure 30;Table 6;Reference 57...