Research On The Mechanical Properties And Failure Precursor Characteristics Of Marble Under Loading And Unloading Conditions

Based on the loading and unloading of deep mining excavation,the mechanical characteristics and failure precursors of surrounding rock mass of deep roadway under unloading conditions are studied in this paper.Taking marble as research object,uniaxial compression test,uniaxial cyclic loading and unloading test,conventional triaxial compression test and constant axial displacement unloading confining pressure test are set up.The mechanical parameters variation characteristics,acoustic emission characteristics,acoustic emission b value characteristics,acoustic emission RA value,loading and unloading response ratio,acoustic emission signal clustering characteristics under four stress conditions are studied.The main research results are as follows:(1)The uniaxial cyclic loading and unloading test of marble is carried out: the stress-strain curve of rock appears hysteretic loop after applying cyclic load,and the area of hysteretic loop increases with the increase of axial load;the deformation modulus decreases first,then increases and then decreases;the Poisson's ratio is relatively stable under the earlier cyclic load,and the acoustic emission increases sharply before the instability;and the acoustic emission mainly concentrates on each cycle.The peak stress of the ring is near,and most of the acoustic emission is generated by the loading stage.The cyclic loading has obvious strength strengthening effect on the rock.(2)Conventional triaxial and constant axial displacement unloading confining pressure simulation tests were carried out.In conventional triaxial tests,the shear failure was the main cause of micro-damage in the early and middle stages of loading,and the tensile failure was the main cause of large cracks in the later stage of loading.In constant axial displacement confining pressure test,high confining pressure can limit rock failure,and the higher confining pressure is,the higher the limit degree is;at high unloading rate,rock is in a fast and continuous failure state until complete failure;at low unloading rate,residual strength after rock failure can limit further rock failure to a certain extent;acoustic emission increases sharplybefore rock failure.(3)Acoustic emission precursors of marble failure under various stress conditions are studied: In uniaxial cyclic loading and unloading test,the counting of acoustic emission ringing,the sudden change of energy,the sharp rise of loading and unloading response ratio and the sharp drop of b value can be used as the path of rock failure precursors.In conventional triaxial and constant axial displacement confining pressure relief tests,the "intensive active period of acoustic emission" can be used as the characteristic information of rock failure precursors.(4)The acoustic emission signals are classified into three types by clustering analysis of the characteristic parameters of ring counting,energy,amplitude and duration.Under uniaxial compression and uniaxial cyclic loading and unloading conditions,the signals with low ring counting and high energy release characteristics of failure precursor anomalies can be used as rock failure characteristic signals.Under the condition of conventional triaxial compression and constant axial displacement unloading confining pressure,the signal with high ring count and high energy release characteristics of failure precursor anomaly can be used as the characteristic signal of rock failure.In this paper,the mechanical properties of marble under different stress paths are studied,and the precursor information of marble instability is studied from various angles,which has a good reference value for the prediction of the instability of surrounding rock mass of deep roadway.