Experimental Study On Acoustic Emission Source Characteristics Of True Triaxial Loading And Unloading Failure Of Coal And Rock

Affected by mining and excavation activities,the deformation and instability of surrounding rock in deep coal mine excavation roadways are becoming increasingly serious,which seriously restricts the safe and efficient mining of coal resources.The essence of deformation and failure of surrounding rock in excavation roadways is the deformation and failure of coal and rock under the action of loading and unloading.Acoustic microseismic/emission monitoring technology has unique advantages in deformation and damage monitoring and disaster warning of surrounding rock in excavation roadways.Therefore,conducting research on microseismic/acoustic emission source characteristics of true triaxial loading and unloading failure of coal and rock is of great significance for real-time monitoring of deformation and failure and disaster warning of surrounding rock in excavation roadways.This thesis focuses on the study of source characteristics of coal and rock loading and unloading failures.The acoustic emission localization monitoring experiment of coal and rock true triaxial loading and unloading failure was carried out.Methods such as theoretical analysis,laboratory experiments,and data processing were used.The source signals induced by coal and rock failure are accurately located,the source mechanism is inverted,and the induced waveform characteristics and parameter time-varying laws are analyzed.The time-varying laws of acoustic emission characteristics for sandstone,raw coal,and coal-rock combinations under loading,unloading,and loading failure are obtained.The main work and relevant conclusions are as follows:The acoustic emission location monitoring experiment of coal and rock true triaxial loading and unloading failure was carried out.The experiments show that:(1)The active degree of acoustic emission signals has a good response relationship with the internal stress changes of coal and rock.During the first two stages of loading,the number of acoustic emission signals was small and the amplitude was low,while during the damage stage,the number of acoustic emission signals significantly increased and the amplitude increased.(2)The loading failure strength of coal and rock is generally higher than the loading and unloading failure strength of coal and rock,and the strength of sandstone is generally higher than the strength of raw coal and coal rock combination.(3)The loading failure strain of coal and rock is generally greater than the loading and unloading failure strain of coal and rock.The failure strain of sandstone is generally smaller than that of coal-rock assemblages and raw coal,which proves that raw coal is more prone to deformation and damage than sandstone.The arrival time of the signal waveform of coal and rock fracture source has been accurately picked up,the coal and rock fracture source has been accurately located,and the spatiotemporal evolution law of coal and rock fractures has been deeply studied.The research shows that:(1)The source location is obviously concentrated near the fractures and fracture surfaces.Source location has a good response relationship to the initiation and development of fractures,as well as the expansion and penetration of fracture surfaces.(2)The loading and unloading process of coal and rock,the seismic source continuously generates on both sides of the minimum principal stress direction of sandstone,forming a fracture surface.The seismic source continuously concentrates inwardly in the direction of the minimum principal stress of the raw coal,forming multiple fracture surfaces.In the coal-rock combination,a large number of seismic sources are generated in the coal part,and then extend into the sandstone.(3)The loading process of coal and rock,The seismic source is generated on both sides of the minimum principal stress direction and the intermediate principal stress direction of sandstone,forming fracture surfaces.The seismic source is located in the direction of the minimum principal stress of the raw coal and forms several fracture surfaces.The seismic source in the coal-rock combination forms several fracture surfaces in the raw coal section,and then extends into the sandstone.The evolution law of the fracture type,the variation law of the source volume,and the spatiotemporal evolution law of the source magnitude of coal and rock loading and unloading damage have been studied.The research shows that:(1)The source microcracks formed by the loading and unloading failure of coal and rock are mainly of the tension-shear composite type,with the tensile mechanism dominating.Source model inversion and polarity analysis are consistent in determining the source tension shear attributes.(2)During the process of coal rock failure,the volume increment of source tension is generally greater than that of shear.The tensile shear volume increment of the raw coal source is similar to that of the coal-rock combination,and is larger than that of the sandstone.The sum of the source tensile shear volume increments of coal and rock loading and unloading failures is greater than the sum of the tensile shear volume increments of coal and rock loading failures.The growth of source tension shear volume mainly occurs in the failure stage.(3)The magnitude of coal and rock fracture sources is mainly distributed in the range of-8.5 to-7.0 magnitude.High seismic events mainly occur during the loading and unloading and loading failure stages of coal and rock.The time-varying law of induced waveform characteristic parameters during loading and unloading and loading failure of coal and rock,time-frequency amplitude characteristics of a single waveform at the moment of coal and rock failure and the entire process of failure,and waveform counting-damage evolution law were studied.The research shows that:(1)The duration of sandstone induced waveform is slightly shorter than that of raw coal and coal rock combination.Sandstone will have a peak amplitude in the 0.1 MHz frequency band,while raw coal and coal-rock combination will maintain a high amplitude below 0.2 MHz.(2)The frequency range of high amplitude waveforms for coal and rock failure is below 100 k Hz,and as the stress increases,the frequency of high amplitude waveforms shows a decreasing trend.Waveform signals with failure characteristics are characterized by a large number,high amplitude,and low frequency.(3)A damage variable based on acoustic emission waveform counting has been proposed,which can intuitively and meticulously reflect the internal damage evolution of coal and rock,and the changes comply with the damage evolution law of coal and rock during loading and unloading failure.There are 99 pictures,7 tables,and 143 references.