Acoustic Emission Characteristics Of Siltstone With Prefabricated Open Fracture Under Uniaxial Compression Process

Occurrence in rock mass is inhomogeneous in nature,non-continuous materials,has experienced the transformation of various tectonic movement and weathering,rock mass within the various defects(cracks,joint,cavity,fault,etc.),caused great damage to the integrity of the rock mass,the lower the strength of rock mass when the load and deformation increases,seriously affected the stability of rock mass.Therefore,the mechanical properties and fracture evolution characteristics of rock mass under load have been paid more and more attention by scholars.The nature of rock mass under load deformation and failure is the evolution process of micro-cracks in rock,and acoustic emission is the associated phenomenon in this process.At the same time,acoustic emission signals generated in the process of rock failure contain a lot of information about the change of crack structure in the rock,and the relationship between acoustic emission signals generated in the process of rock failure and various mechanical parameters of the rock can be studied,so as to further deepen people's understanding and understanding of the process and nature of rock material failure.In this article,through the cylinder siltstone specimens through crack open type,different perspectives on the surface of the precast using acoustic emission monitoring method,experiment of uniaxial compression loading damage from rocks and key in the whole process of the feature points,carry out with precast cracks in the process of rock damage its internal structure change to answer all the transmitting refinement study,different Angle prefabricated crack sample were in the process of damage acoustic emission rule,the conclusion is as follows:(1)Through uniaxial compression experiment,the influence law of precast fracture dip Angle on failure load,deformation and failure mode of siltstone sample was analyzed.It can be seen from the analysis that the failure load of the sample has a negative linear correlation with the Angle of the precast crack,while the axial deformation tends to decrease with the increase of the precast crack Angle.In terms of failure mode,the failure mode of the complete siltstone sample is x-shaped conjugate plane shear failure,and the failure mode of the sample with prefabricated fracture varies with the change of dip Angle: when the prefabricated fracture Angle of the sample is 0°,the failure mode of the sample is single inclined plane shear failure.When the prefabricated fracture dip Angle is 30°,45° and 60°,the failure mode of the sample is tensile shear composite failure.When the dip Angle of sample precast crack is 90°,the failure mode of sample is split failure.(2)Through the collected in the process of rock under uniaxial compression experiment of the acoustic emission signal were analyzed,and got the following rules:(1)by analyzing the ringing count complete specimen failure process can be divided into consolidation stage,elastic stage of crack,crack stable propagation stage,crack penetration destroy stage four stages,including the prefabricated crack sample with prefabricated crack obliquity of the acoustic emission signals are different,and change has obvious characteristic;(2)by analyzing the energy count,the failure process of the complete specimen can be divided into three stages: energy input stage,energy stable release stage,and energy rapid release stage.With the increase of the inclination Angle of the precast crack specimen,the instantaneous overload energy release phenomenon becomes more and more obvious in the energy release process.(3)The acoustic emission ringing count can better reflect the occurrence of single crack propagation during the failure process of the specimen,while the energy count can better reflect the failure process of the rock in the macroscopic aspect during the detection.(3)Maximum likelihood estimation method is used to calculate and analyze acoustic emission b value,and the following conclusions are drawn: acoustic emission b value of complete siltstone sample has obvious stage characteristics,and its b value fluctuates up and down very little in each stage;The b value of the precast crack specimen also has periodic characteristics,but with the increase of the precast crack inclination,the periodic characteristics of its change become less and less obvious.The b value of all samples fluctuates significantly in the relatively quiet period of ae,which can be regarded as an obvious sign before rock failure.(4)The acoustic emission software is used to obtain the three-dimensional positioning image of the acoustic emission event and make a comparative analysis with each stage of rock failure.Acoustic emission events three-dimensional positioning map each stage in the process of siltstone specimens damage showed significant stage characteristics,with the increase of prefabricated crack Angle,specimen crack in the process of damage and fracture zone of the development of present different rules,the fracture zone distribution and final failure mode corresponding to the specimen,three-dimensional positioning can let us more intuitive understanding of the specimen on the space development process of the internal crack.(5)According to the damage curve of Weibull function and acoustic emission parameters,a statistical damage model based on acoustic emission parameters was established.It is concluded that there are two stages in the process of failure: the stage of damage stabilization and the stage of damage rapid growth.It can be seen from the damage-strain curve that there is an obvious inflection point between the two stages.After the inflection point,the damage increases rapidly and the sample fails rapidly.Therefore,the judgment of the inflection point of the sample damage is crucial to the judgment of the instability of prefabricated fracture brittle rock.