Study On The Characteristics Of The Electromagnetic Emission And Acoustic Emission In Rock Under Stress Wave

The electromagnetic emission(EME) during rock failure attracted much interest of domestic and overseas researchers in recent years.The acoustic emission(AE) during rock failure is known much earlier,in fact, many scholars studied both the EME and AE at the same time because both of them are considered to be related to microfractures during rock deformation and obtained inaugurated achievements.At present,the study on the EME are mainly focused on the experimental work,however,there are few theoritical studies especially about its emission mechanism;the obtained results of AE are mainly about cases that rocks are experienced static load,while the study on the AE of rock subjected to impact and static-dynamic coupling loading is strictly not enough.Supported by national natural science foundation of china,the author studied the EME in intact rock and jointed rock subjected to stress wave and the AE in rock under static-dynamic coupling loading in the dissertation.(1) The EME induced in the rock containing piezoelectric materials has been investigated both under static stress and stress wave in the view of piezoelectric effect.The results show that the intensity of the induced EME in the rock under static loading increases with the rising of the stress level and the loading rate;the relations between the EME amplitude and elastic parameters and propagation distance are presented under different modes of stress wave.The intensity of the EME relates not only to the strength and elastic modulus of rock masses,but also to the initial damage levle of the rock.The EME intensity induced by stress wave reaches to the highest in the explosion-center and attenuates with the propagation distance.The EME intensity increases with the rising of the elastic modulus and decreases with the rising the initial damage.The results are in good agreement with the experimental results.(2) According to the obtained relation between electromagnetic wave and incident stress wave and the resolution of the transmitted coefficients in the joint,the strength variation of the EME before and after the joint when the normal incident stress wave propagates to the linear deformative joint has been presented.The effects of such parameters as initial joint stiffness,the electric parameters of the rock masses and incident frequency on the intensity variation of the EME are investigated. The results show that the EME intensity increases with the increase of the joint stiffness;the higher frequency EME attenuates much more rapidly than the lower frequency signals.In the case of the characteristics of two sides of the joint being different,the change of the EME intensity with a single parameter is clear,however,the intensity variation of the EME will be complicated due to the comprehensive effect of many parameters.(3) Based upon the achievements(1) and(2),the further research on the effect of the nonlinear deformative joint on the EME strength is completed.According to the resolution of the transmitted and reflected coefficients when the normal incident P-wave propagates to the nonlinear normal deformative joint,the expression between the intensity variation of the EME and the parameters of the joint is obtained.And the effects of such parameters as the joint deformation and incident frequency on the intensity variation of the EME are investigated.The results in this dissertation explain some electromagnetic perturbations during seism and during rock failure.(4) Based on the thesis of the EME induced by atomic perturbation due to propagating crack during rock fracture,the relation between EME frequency and rock's attribute parameters has been obtained through the relation between the EME frequency and crack width calculated using the Crack Opening Displacement method.The dependence of the EME frequency on each attribute parameter has been discussed.The results show that EME frequency increases with the increase of the elastic modulus and decreases with the increase of the size and strength of rock samples.The change of the EME frequency with the poisson ratio is affected by the elastic modulus as well.The effect of the initial length of the crack on the frequency correlates to the size of the rock.And the EME frequency values induced by several kinds of common rocks fracture have been calculated.It is shown that the order of the magnitude of the frequency of the single pulse EME reaches 10~5 Hz.The EME amplitude increases with the elastic modulus;the amplitude correlates to the dimension of the rock and the influence of the dimension is greater than lithology on the EME.The results in this dissertation are in agreement with the existing experiments.(5) The experiments are completed under static-dynamic coupling loading on the SHPB system.The effect of different static load and dynamic load on the AE parameters is investigated and the AE law is obtained under static-dynamic coupling loading.The empirical formula of the AE energy is presented under coupling loading based on analyzing large experimental data and the fitting results are good agreement with the experimental results.The fractal property under coupling loading is studied and the relation between the peak of AE energy and fractal dimension value is obtained.The results show that the larger the fractal dimension value D,the smaller the peak of AE energy.(6) Through the research on the EME and AE induced in rock under dynamic loads,we found that the features of both the EME and AE are related to the loading mode,material properties and initial damage level and are different from the characteristics under static loads.Both the EME and AE can reflect somehow the damage degree during material fracture,thus,it is more meaningful to combine their advantages to predict material failure and monitor the mine safety.In short,the research of this dissertation,facecd to front of the subject, used the newest mathematical and mechanical methods and means to investigate the characteristics of the EME in rock under stress wave and the AE in rock under static-dynamic coupling loading,the results obtained are useful for both theory and practice to use the EME and AE technology to evaluate correctly the stability of rock mass engineering.