Study On The Tendency And Acoustic Emission Characteristics Of Limestone Explosion In Different Depth

In recent years,due to the depletion of shallow resources,human beings are gradually expanding to the deep.With the development of underground engineering,rock burst disasters occur frequently.Therefore,on the basis of reading domestic and foreign literature and summarizing relevant research results,the core of a new main shaft project of a copper mine in Jiangxi province is taken to carry out the test,and the main physical and mechanical properties of limestone with different burial depth are tested.The RMT-150 C rock mechanics test system and PCI-II acoustic emission acquisition system are used to carry out the single axis test of unconfined rock The compression rock burst test and acoustic emission test are mainly used to analyze the acoustic emission characteristics of the limestone in the depth of 400-1000 m under different rock burst tendencies.The fracture mode of the limestone in different depths are studied by the combination of the mixed Gaussian model and the macro and micro view.The main research work and conclusions are as follows:(1)By analyzing the data of compressive strength,Poisson’s ratio and modulus of elasticity of limestone under the condition of different burial depth in the process of uniaxial compression failure,it is found that the modulus of elasticity of limestone samples at different depths increases obviously with the increase of depth,but Poisson’s ratio has no obvious difference;from the perspective of uniaxial compressive strength and density of rock,the test values of limestone samples at different depths generally present Increasing trend.(2)According to the loading and unloading test results and the classification standards of rockburst tendency,the rockburst tendency of different depths of limestone is judged,and it is concluded that there is no rockburst tendency of 400-600 m depth limestone,weak rockburst tendency of 700 m depth limestone,medium rockburst tendency of 800-900 m depth limestone and strong rockburst tendency of 1000 m depth limestone.With the increase of the burial depth of the sample,the tendency of limestone rockburst is stronger.(3)The basic characteristics of AE can be divided into three stages: initial stage(I),stable stage(II)and active stage(III).As far as the active stage is concerned,the acoustic emission ring count of rock samples at all depths shows the characteristics of significant increase,and the peak point of stress increases sharply,while the b-value of acoustic emission decreases at this stage;the r-value of acoustic emission shows the trend of increasing in the compression stage,decreasing in the elastic stage and decreasing in the instability stage during the bearing process of limestone samples;from the main stage of acoustic emission From the frequency point of view,the main frequency of non rockburst to strong rockburst prone limestone is mainly the low frequency between 100-170 kHz,but the main frequency band of medium and strong rockburst prone limestone also has the secondary main frequency between 270-330 kHz.(4)According to the analysis of the macro failure modes(tensile failure,shear failure and tensile shear failure),with the increasing tendency of rock burst,the failure modes of limestone have the development trend from tensile failure to tensile shear failure,and then from tensile shear failure to shear failure;the limestone fragments after uniaxial failure are observed by metallographic microscope,and analyzed according to the imaging results To: with the increasing tendency of limestone explosion,the worse the flatness of fracture surface,the more prominent the crystal particles on the surface,and the more obvious the particle scratch.(5)The results show that with the increase of stress level,the proportion of rock shear crack signal increases gradually,and the stage with the largest proportion of shear crack signal is in the middle and late stage of rock failure.In addition,with the increase of rockburst tendency,the proportion of acoustic emission signal of shear crack of limestone sample increases gradually,which means that the internal failure of limestone sample is stronger and stronger in the form of shear crack,and weaker in the form of tensile crack.