Study On Mechanical Properties Of Marble Under True Triaxial Unloading Under High Stress Conditions

With the increase of underground mining depth,rock burst has a growing trend to the threat of mining production.The true triaxial rock burst test system is used to simulate the force path of the surrounding rock of the deep mining roadway.The rock burst test at different unloading rates is studied from the deformation characteristics,mechanical characteristics and debris characteristics and other aspects of the rock burst characteristics of the study.(1)Through the analysis of the stress-strain curve and mechanical para meters after the failure of the marble,it is found that the unloading rate has little effect on the intermediate principal strain;Rock burst is caused by the expansion,with a certain burst;the greater the rate of unloading the expansion of the phenomenon is more serious;the strength of rock burst increases as the unloading rate decreases;through the marble after the destruction of the shape we can see,the crack after the failure of the marble under different unloading rates is parallel to the axial loading direction of the rock specimen,the degree of fragmentation of the rock increases with the increase of the unloading rate,and the debris is dominated by flake and strip,which belongs to the typical splitting.(2)From the analysis of acoustic emission characteristics,the higher the unloading rate,the greater the emission energy value;during the unloading phase,the acoustic emission energy of the rock increases and the counting increases,the time at which the acoustic emission count appears is significantly earlier than that of the acoustic emission;according to RA value and RA-AF scatter distribution characteristics analysis,it is concluded that the cracks produced by the rock burst test at different unloading rates are the composite shear cracks.(3)Through the analysis of the characteristics of the debris of the rock,the higher the unloading rate,the higher the proportion of the smaller particles with the smaller particle size,and the more severe the rock burst;the fractal dimension of the length/width/thickness-quantity is the smallest,which can be used as the priority measure of the fractal dimension of rock burst;The size of the fractal dimension is positively correlated with the difficulty of crushing,and the value decreases with the decrease of the unloading rate.Based on the true triaxial rock burst test system,the rock burst test of the marble is unloaded,and the process of rock burst induced by excavation unloading is reproduced.In this paper,the strength,deformation characteristics,acoustic emission characteristics and fractal characteristics of rock burst under high stress unloading condition are studied deeply.The research results can provide reference for future rock burst test and practical engineering application.