Study On Optimal Arrangement Of Rock Sample Acoustic Emission Sensor And Coupling Law Of Multi-parameter Information Characterizing Fracture Development

The development and penetration of fracture is the basis of rock failure,which is an obvious nonlinear evolution process in time and space.It is an important part of exploring the law of fracture development in coal and rock mass to realize effective monitoring methods and reasonable characterization means for this process.Based on this,this paper combines theoretical research with acoustic emission experiment.Firstly,the arrangement of acoustic emission sensors in laboratory is optimized,and the Double-layer Wrap-around Arrangement of acoustic emission sensors and the corresponding polar coordinate positioning algorithm are proposed to improve the monitoring accuracy.Secondly,the acoustic emission response characteristics of the loaded rock samples are analyzed.The damage mechanism and crack propagation law of sandstone specimens are studied from the microscopic point of view.Finally,the damage and fracture process of sandstone is coupled with the multi-parameter information of acoustic emission,and the multi-parameter index of acoustic emission is used to represent the fracture development process of sandstone.Combined with the engineering site,the monitoring and early warning index of acoustic emission is put forward.The results are as follows:(1)According to the polar coordinate localization algorithm,the Double-layer Wrap-around Arrangement of acoustic emission sensors is proposed.The coordinates of the acoustic emission source based on the polar coordinate algorithm are(r,q,h).The formula is as follows:(?)The positioning results show that the positioning accuracy of the acoustic emission source is only related to the number and arrangement of the sensors when the sample size,arrival time,and wave speed are constant.The double-layer wraparound arrangement of the acoustic emission sensor effectively improves the positioning accuracy within the monitoring range.(2)The law of fracture development during the process of damage and rupture of the loaded rock mass is obtained.In the process,the damage and fracture process of the loaded rock mass has been accompanied by the development and expansion of the fracture.Among them,the compaction,elastic and plastic phases have large energy level rupture,and all micro-fractures are generated from the rupture of these larger energy levels and expanded to the edge.The internal stress of the loaded rock mass evolves from the initial uniform distribution to gradually generate local stress gradients,and forms a continuously increasing strip-like high stress region.The increase of the local stress difference aggravates the damage of the rock mass.As the loading progresses,micro-fractures are generated in large quantities and extend to the edge of the rock sample,eventually forming a large-scale macroscopic through-fracture.The final location of the rupture surface is determined by the internal evolution process of“small energy micro-fracture—large energy rupture—fracture penetration”.(3)The constitutive equation of the sandstone damage model based on AE energy characteristics is established,which can better reflect the failure process of the rock sample from the linear elastic transition to the plastic deformation phase,especially the plastic deformation to the post-peak stage.The difference in lithology and the change of loading mode will lead to differences in rock damage process and fracture propagation mechanism.Rocks with loose internal porosity are slowly damaged,while structures with dense structures have low initial damage,while plastic phase damage increases sharply.The internal damage of rock under cyclic loading and unloading is mainly tensile failure,while the internal crack of sandstone under uniaxial pure static load is mainly shear crack.(4)The multi-parameter acoustic emission index is established to characterize the fracture development process of rock mass.During the rock loading process,the acoustic emission activity S and the the acoustic emission fault total area A(t)of show a trend of“decreasing—remaining at a low value—increasing—remaining at a high value”with the increase of stress level,and the acoustic emission b-value show a trend of“low value—b value rise—b value decrease—continuous low value”,which corresponds to the four stages of“fracturecompactionadjustment—fractureelasticdeformation—fracture development—fracture expansion”of rock.The acoustic emission activity S and the total fault area A(t),the cumulative damage D value are positively correlated with the acoustic emission signal amplitude,the number of events,and the rupture release energy,where the acoustic emission b value is negatively correlated with it.Acoustic emission multi-parameter index has a high coupling degree with rock fracture distribution and damage degree,which can be used to establish laboratory small-scale monitoring and early warning indicatorsThe research results of this paper enrich the rock damage determination index and improve the accuracy of acoustic emission monitoring and prediction,and further understand the damage and failure mechanism of rock mass in actual engineering.It is important to give theoretical significance and application value to the acoustic emission warning method of coal and rock mass damage.