Microfracture Mechanism Of Pre-cracked Rock Specimens From The Acoustic Emission

The geostress field is disturbed by the engineering construction.The redistribution of geostress fieldinduces fracture propagation of joints and further results in the large deformation and failure of surrounding rockmass.To date,the fracturing mechanism,coalescence process and failure modes of jointed rock mass have been thoroughly studied theorectically and experimentally.And the research outcomes have been widely applied to evaluate the deformation and strength of jointed rock mass.However,these outcomes cannot be used to dynamically interpret the fracture mechanism of jointed rock mass induced by excavation disturbance,because jointed rock mass has a heterogenous structure with different fissures from mesoscale to macroscale and the redistribution of geostress induced by excavation unloading in deep engineering also becomes complicated.Therefore,it is of more practical significance for solving related engineering problems to inverse joint rock fracture propagation mechanism based on the monitoring data from monitoring method.Starting from the mechanism research,this thesis used the acoustic emission(AE)technique and moment tensor inversion theory to investigate the microfracture mechanism of pre-cracked rock samples.The aim is to interpret the microseismic data based on the similarity of the acoustic emission and microseismic monitoring technique.In this study,two types of rock are selected i.e.granite and fine sandstone.The microfracture mechanism of the two types of rock under tensile and compressive-shear loads was studied by the moment tensor inversion theory based on the acoustic emission data from the three-point bend tests and experiment and uniaxial compressive tests for the specimens with preexisting cracks of different orientation angles.Moreover,the influence of lithology on the microfracture mechanism was discussed..The main works are as follows:(1)Based on elastic wave and moment tensor theory,the calculation for moment tensor inversion process has been implemented using computer,and a corresponding code for this was developed by MATLAB language and three-dimensional display program for AE events was done by 3ds Max scripts language;(2)Three-point bend tests for granite and sandstone were accomplished using the AE technique.The microfracture mechanism during the crack propagation under tensile loading conditions at the macroscale was inversed by the moment tensor theory based on the AE data from the tests.Further,the effect of diagenesis on rock micro fracture mechanism was discussed;(3)Uniaxial compressive tests for different penetrated pre-cracked angle specimens,were accomplished.The fracture modes for pre-cracke rocks were analyzed and the effects of crack geometry on crack propagation were discussed.The microfracture mechanism of crack propagation under compression was intensively studied.Moreover,the effects of diagenesis and rock composition on the microfracture were also discussed.The results showed that the shear fracture is fierce at the microscale for the crystal rock while the tensile fracture is strengthened at this scale for cemented rock.