| The deformation and strength characteristics of brittle rock given under complex geological conditions are significant foundations for studying the mechanical properties of rocks.Therefore,it is necessary to thoroughly study the deformation and strength characteristics of the whole process of rock failure,so as to reveal the rock failure mechanism under confining pressure effect.At present,under static load,the acoustic emission ∑N/∑E and RA values are used to predict and forecast the rock buckling failure under the confining pressure effect.In addition,the quiet period of acoustic emission before complete rock rupture under triaxial compression is studied,which is of great significance for the exploration of rock burst precursor information.In this paper,the triaxial compression acoustic emission test of red sandstone is conducted on the basis of the National Nature Fund project "The primary frequency characteristics and energy mechanism of acoustic emission from rock under the action of infiltration pressure"(No.5170040924).And Jiangxi Provincial Natural Science Fund for Youth Fund Project "Acoustic Emission Sound Source Mechanism and Principal Frequency Characteristics of Granite Creep Based on Moment Tensor Analysis"(No.20171BAB216022)The deformation and strength characteristics of red sandstone are mainly analyzed,the relationship between mechanical parameters and confining pressure is discussed,and the acoustic emission characteristics of red sandstone under various confining pressure effects are also studied.On this basis,the relationship between the crack change law and acoustic emission characteristics during rock loading was established.A method of predicting instability failure of red sandstone under triaxial compression based on acoustic emission is proposed.Finally,the quiet period of acoustic emission before complete rupture under the confining pressure effect of red sandstone is studied.The sounding period of acoustic emission is quantitatively analyzed by damage variable to quantify the rupture of red sandstone.Precursor information also discusses the relationship between the development of cracks and the quiet period of acoustic emission during the entire process of rock instability.The results show that:(1)The triaxial compression characteristic strength points(σcc,σci,σcd)values of the red sandstone are obtained by Martin’s crack volumetric strain method.It is demonstrated that confining pressure has a great influence on the deformation and strength characteristics of red sandstone,and the fracture angle of red sandstone graduallydecreases with the increase of confining pressure.(2)The acoustic emission levels(number of events,ring counts,energy ratios)of red sandstone destruction under confining pressure effects from the initial stage of loading to the closure stress σcc and closure stressσcc to The crack initiation strength σci is smaller,but the acoustic emission becomes active gradually in the interval between the rupture strength σci and the damage strength σcd,and the expansion stress(ie the damage intensity)After σcd),the acoustic emission level significantly increased,and there was a sudden increase in the vicinity of destruction,the acoustic emission characteristic parameter reached a maximum value,and the slope k value of the accumulated ring count of acoustic emission reached a maximum.Under the effect of confining pressure,the time distribution characteristics of acoustic emission parameters and the stress-time characteristics of red sandstone samples are not completely synchronized.The maximum value of acoustic emission parameters obviously lags behind the macroscopic destruction time of red sandstone.(3)Primary characteristics of acoustic emissions in red sandstone under triaxial compression:As the external load increases,the primary frequency of the acoustic emission gradually broadens,and there is a main frequency band of 300～400 kHz,0～50 kHz before the rock ruptures.The frequency characteristics can be used as a precursor to the triaxial compression buckling failure of red sandstone.During the loading process of the red sandstone,the acoustic emission r values showed large fluctuations at the initial stage of loading,then decreased and remained stable,and then the r value increased,and the r value dropped sharply before the peak intensity;while the acoustic emission b value was overall.The fluctuations are large,and they suddenly drop before the peak intensity.The above characteristics of the acoustic emission r value and b value can be used as a method to predict the destruction of red sandstone.The newly proposed acoustic emission RA values were used to analyze the development of cracks in the deformation and failure process of red sandstone.From the analysis of the RA characteristics of acoustic emission at different confining pressures,the acoustic emission RA values were spatially distributed in the initial period of triaxial loading of red sandstone.A small amount and random,low confining pressure RA values appear in the middle and high areas,so mainly in tension cracks,shear stress cracks dominated in the high confining pressure RA value areas.With the progress of loading,the tensile cracks in the low confining pressure are mainly concentrated in the shear zone with a small amount of shear cracks.When the confining pressure is high,it is found that the acoustic emission in the red sandstone accounts for a large proportion of the shear cracks and is diffusely distributed.(4)The slope of the damage variablecurve increases,decreases,and increases to quantitatively analyze the acoustic emission quiet period,and decreases the slope time period as the quiet period of acoustic emission.As the confining pressure increases,the acoustic emission quiet period increases.The duration will be extended.The ratio of the quiet period to the peak load duration will increase with the increase in confining pressure.The relationship between the development of cracks in red sandstone and the quiet period of acoustic emission will be established.The cracks in the cracks are dominated by shear cracks. |
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