Mechanical Properties and Acoustic Emission Characteristics of Limestone Under Triaxial Loading
Limestone is one of the sedimentary rocks widely distributed in coal mines,and it is very important to reveal its mechanical properties and damage evolution process for the safe mining of coal resources.Triaxial compression tests under different confining pressures were carried out on limestone samples taken from the floor of-950 m return air cross-cut in No.81 mining area of a mine in Huaibei,and the whole process of deformation and failure of limestone was monitored by acoustic emission.The test results are concluded as follows.(1)The stress-strain curve of limestone can be divided into four stages.With the increase of confining pressure,the elastic modulus E,poisson's ratio μ,cracking stress σci and peak stress σpv increase,but the closing stress σc remains basically unchanged.The stress ratio σc/σpv decreases with the increase of confining pressure,but σci/σpv and σr/σpv are not sensitive to the change of confining pressure.The cohesion and internal friction angle at the residual stress σr are reduced by 18.94％and 26.27％respectively compared with the peak stress.(2)The evolution of acoustic emission(AE)can better characterize the asymptotic failure process of limestone,and the evolution law of acoustic emission of limestone under different confining pressures is consistent.The peak value of ringing count decreases with the increase of confining pressure,and the amplitude of acoustic emission is distributed in the range of 20-100 dB.The high-amplitude AE events in the limestone sample will increase with the loading of axial stress and show an aggregated distribution.(3)The damage evolution model established by using the cumulative ringing count as the characteristic parameter can better describe the asymptotic failure process of micro-fracture closure,expansion,penetration and macro-failure in limestone under triaxial stress.
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