Study On Mechanical And Acoustic Emission Characteristics Of Rock Under Baroclinic Boundary Stress

With the deeper exploration of the project,the occurrence environment of deep rock mass becomes more and more complex.The geomechanical characteristics of deep rock mass determine that the obvious difference between deep rock mass and shallow rock mass lies in the special environment of deep rock mass,that is,the complex mechanical environment of "three high and one disturbance(high ground stress,high ground temperature,high karst water pressure and mining disturbance)".In deep underground engineering construction,high geo-stress is one of the main causes of engineering geological disasters.After roadway excavation,there will be a certain Angle between roadway and ground stress in space,which is called tunnel baroclinic ground stress,and the stability of roadway surrounding rock varies with different Angle relationships.Therefore,based on the axial Angle change of roadway as the main line,this study studied and analyzed the mechanical properties and acoustic emission characteristics of prefabricated granite circular holes and horseshoe holes with different cross-section shapes under certain confining pressure conditions.At the same time,DIC digital speckle technique was used to analyze the crack initiation,propagation and penetration process from the microscopic point of view.The main work and research results of this paper are as follows:(1)Biaxial compression tests were carried out on prefabricated circular hole rock and prefabricated horseshoe hole rock,and the strength variation law under different axial angles(the included Angle between the axis direction of roadway and the maximum horizontal principal stress)was analyzed.The results show that the cross-section shape of roadway has a certain influence on the overall strength of rock.It is found that the rock strength of prefabricated circular cavity under axial parallel condition(axial angular deflection plane is parallel to the direction plane of maximum principal stress applied)is basically stronger than that under axial vertical condition(axial angular deflection plane is perpendicular to the direction plane of maximum principal stress applied).However,the strength of prefabricated circular hole rock shows no such strength law.(2)Acoustic emission technology was used to detect the whole process of biaxial compression test of prefabricated circular hole rock and prefabricated horseshoe hole rock,and the variation characteristics of acoustic emission parameters in different axial angles were investigated.Based on the analysis of AF-RA kernel density distribution and peak frequency(PF)ratio,the rock failure modes can be identified.The number and size of microcracks in the whole process of rock compression were investigated by AE counting rate,AE impact rate,AE energy variation and cumulative AE parameter values.The precursor of rock failure is studied by combining the trend of acoustic emission dynamic b value.The results show,the failure mode of prefabricated circular hole rock and prefabricated horseshoe hole rock is a type of pull-shear failure,and the tensile crack is the dominant type.The AE counting rate has a certain synchronization with the variation trend of AE energy,and there is a pseudo-quiet period before rock failure.In the early stage of stress,dynamic b tends to fluctuate slightly in the range of 1.0-2.0,and begins to decline after 80% of the peak strength,and to the minimum at rock failure.(3)DIC digital speckle technology was used to deeply analyze the whole process of crack initiation,propagation and penetration under biaxial compression test of prefabricated rock.The 2D-DIC digital speckle data processing by open-source code named "Ncorr”,the Ncorr was used to obtain the evolution cloud map of full strain field.The results show that cuttings peeling or falling off the inner wall of roadway will appear before the macroscopic cracks on the rock surface,and the peeling phenomenon of the inner wall of roadway starts to occur between 60% and 80% of the biaxial peak strength.For the prefabricated circular hole rock,the crack propagation modes are similar under the axial parallel and axial vertical conditions,while the prefabricated horseshoe hole rock has obvious differences.In the prefabricated horseshoe hole rock,under the axial parallel condition,the high strain localization zone mainly occurs at the top of the tunnel and the sharp corner at the lower left corner of the tunnel.Under axial and vertical conditions,high stress localization zone mostly appears near the straight edge of horseshoe shaped roadway.This conclusion has important practical guiding significance for the early support and late maintenance of surrounding rock of deep engineering body with high stress.