Rock Failure Mode Analysis Based On Acoustic Emission (AE)

Rock mass fracture instability has always been a key issue in rock mechanics research at home and abroad.The occurrences of geotechnical engineering disaster(Such as rock bursts,rock collapses,rock landslides,etc)are often associated with rock rupture instability process.How to use scientific and effective technical methods to systematically study the dynamic evolution of internal micro fracture in the process of rock fracture instability is of great significance for understanding and understanding the failure mechanism of rock mass rupture and effective monitoring and early warning evaluation.Acoustic emission(AE)detection,as a new nondestructive testing,is very suitable for dynamic safety detection,monitoring,integrity evaluation,early warning and failure prevention of rock failure.This paper combines on-site investigations and laboratory tests,and on the basis of extensively studying and summarizing domestic and foreign research results,we took the mudstone and sandstone of Duanqu landslide in the Nanjiang and the Kualiangzi landslide in the Zhongjiang County,and the limestone of the Daguangbao Landslide in Qingchuan County,the granite of the 213 Shimian highway intersection of National Highway.XRD ray diffraction analysis was used to analyze the mineral composition of the four rocks.Through the MTS815 Flex Test GT rock mechanics test system and the acoustic emission test acquisition system PCI-2,the acoustic emission characteristics of the four rocks under different loading conditions were analyzed.The fracture modes of four rocks under different loading conditions were studied by the JCMS-? b5706 parametric analysis method,Gaussian mixed model(GMM)and G-P fractal theory.(1)The main protolith of granite,limestone,mudstone and sandstone is feldspar,dolomite,quartz and quartz.The content of feldspar and quartz in granite reaches 95%,and these coarse-grained minerals make the granite heavy and strong.Limestone has a single mineral,and the content of dolomite is 95%.Mudstone and sandstone of red strata area quartz content were 64%and 47%respectively,the mudstone in the ferric iron ion hematite,this is a major cause of mudstone color to red,and mudstone has occurred in the sandstone of no clay mineral of illite,plagioclase content is 20%higher than that of mudstone.The existence of two kinds of coarse minerals,quartz and feldspar,leads to lower diffraction peaks of other minerals.It is due to the differences in the content of mineral composition in the rock,which leads to the differences in the physical parameters,strength and acoustic emission characteristics of various rocks.The strength of the uniaxial loading rock was the DH>DG>DN>DS2,and the strength of in the Brazilian loading was the PG>PH>PN>PS2.(2)The stress-time-event number curve,stress-time-energy-accumulation energy curve and time-count-amplitude three-dimensional histogram of the uniaxial compression and Brazilian of the four rocks were analyzed,and the uniaxial compression were found.In the lower brittle rock granites and limestones,there was a"periodic" period,but mudstones and sandstones did not appear.The number of acoustic emission events under Brazilian loading was significantly lower than that under uniaxial loading conditions.The energy and time axis were triangularly distributed and the cumulative energy curves are all stepped up.(3)Through JCMS-? b5706,the distribution of RA-AF scattered points of granite,limestone,mudstone and sandstone under the condition of uniaxial compression and Brazilianting loading.It is found that four rocks specimens in each time period show low AF values corresponding to high RA values and low RA values corresponding to high AF values,which conform to the characteristics of tensile cracks and shear cracks.However,the distribution of RA-AF scattered points is different because of the different lithology and loading methods.The RA-AF data points under uniaxial compression are more than the Brazilianting loading mode,and the data points of granite and limestone are more than mudstones and sandstone.There are few data points of shear crack under Brazilianting loading.Statistics of the granite,limestone and mudstone and sandstone under uniaxial compression and Brazilianting each load stage in the tension failure and shear failure of the acoustic emission count and the proportion of their respective,quantitative gives each damage stage tension cracks and shear crack.At the same time,the distribution of three dimensional acoustic emission events spatial location of the stress increment??=0.1?c(?t)(?t)of stress range and each accumulated stage is studied.A series of dynamic characteristics,such as the generation,expansion,pattern and space-time distribution of the tensile and shear cracks of the granite and limestone specimens during uniaxial compression and Brazilian loading,are revealed.The number of acoustic emission events collected and mudstone and sandstone of red strata area is very less,and it cannot accurately reflect the evolution of cracks.(4)Based on the Gaussian mixture model(GMM)and the moving average filtering method(MAFM),the transformation and evolution of tensile and shear cracks of four rocks at each loading stage under uniaxial compression are analyzed.At the same time,the RA and AF values of the shear crack cluster and the tensile crack cluster center different loading stages and the two types of crack proportion at each loading stage are also given.It is found that the maximum ratio of shear crack appears at the stage of(0.8?0.9)?c.This time period corresponds to the middle and late stage of the unsteady expansion stage in the rock loading process.The maximum ratio of shear crack can be used as a precursor threshold for predicting rock failure.(5)The correlation coefficients of the original data of four rocks fractal dimensions under uniaxial compression and Brazilianting conditions are 0.84 and 0.81 of the regression lines at each loading stage,indicating that the fracture of the four rocks under different loading has fractal characteristics.The fractal dimension of mudstone and sandstone in the red strata area under uniaxial conditions is obviously larger than that of granite and limestone,indicating that the acoustic emission activity of granite and limestone is stronger than that of mudstone and sandstone.The fractal dimension of acoustic emission under Brazilian loading is generally larger than that under uniaxial loading,which shows that the acoustic emission activity under uniaxial loading is stronger than that under Brazilian loading.During the whole loading process,the fractal dimension is a process of first increasing dimension and then decreasing dimension.In the initial stage of loading,the interior of the rock is mainly micro fracture and micro damage,and their distribution has uniformity and randomness.The fractal dimension of acoustic emission is larger and the rock is disordered structure.After that,it descends gradually and reaches the minimum value when rock is destroyed.It shows that the disorder of rock is orderly transformed,and the internal damage of rock continues to increase,and from disorder to macroscopically ordered destruction structure.The fractal dimension of acoustic emission can be used as an indicator to describe the mechanical and structural damage of rock,and it can reflect the complexity of the spatial distribution of acoustic emission.The obtained fractal dimension can be used to describe the characteristic parameters of rock failure.