Experimental Study On The Relationship Between Acoustic Signal Of Granite And Its Characteristic Intensity Under Uniaxial Compression

Rock deformation and failure are accompanied by acoustic emission and infrasound signals,and the frequency of rock acoustic emission is usually 1kHz¹MHz and frequency of infrasound ranges from 0.01 Hz to 20 Hz.There are a lot of literature on the study of the two kinds of signal characteristics of rock deformation and failure,but few researches which monitoring and characteristic analysis for acoustic emission and infrasound in the process of deformation failure has been done.In this paper,the acoustic emission and infrasound tests of granite under uniaxial compression are carried out,and the acoustic signal characteristics of these two frequencies during deformation and failure are obtained and analyzed jointly.The rock peak precursor characteristics based on the comprehensive analysis of acoustic emission and infrasound signals are explored,which provides experimental basis for the joint monitoring and prediction of rock failure by acoustic emission and infrasound waves.The main results and conclusions are as follows.?1?The average compressive strength of granite was obtained by 135.9MPa,and the peak strain was between 0.32%⁰.55%,which belonged to hard brittle rock.The crack strength?_cii is 58.9⁶9.15MPa,the corresponding stress percentage is 43%⁵4%.The damage strength?_cdd is 93.1¹19.8MPa,the corresponding stress percentage is 72%⁸8%,and the rupture form is mainly shear failure.?2?The acoustic emission events rate remains low at the compaction stage and the elastic stage which is before the crack initiation strength.When the stress exceeds the initiation strength,the AE events rate increases significantly.And before the peak stress,the AE events rate decreases to a varying degree and there is a transient"relative quiescence".The ringing count and energy rate of acoustic emission mainly focused on the unstable growth stage of the crack,that is after the damage intensity point.At the peak intensity point,the energy rate rises straight up to the maximum and the ringing count reaches the maximum value.The main frequency of acoustic emission is mainly distributed in the 100¹30kHz band during the whole test.After the damage intensity point,the main frequency is concentrated in 200²50kHz and300kHz.?3?The main frequency of the rock infrasound signal is concentrated in 5¹5Hz,and the proportion of infrasound dominant frequencies between 0-5Hz and 15-20Hz fluctuates continuously,and reaches the lowest in the corresponding stress level segments of 80%-100%..By analyzing the fractal characteristics of infrasonic wave energy and main frequency,it is found that the infrasound energy rate and main frequency have better fractal characteristics,and the fractal dimension of energy will decrease obviously before rock breaking.The fractal dimension of the main frequency will decrease to the minimum before the peak value,which can be used as the precursor of rock failure.?4?Acoustic emission and infrasound signals are reflected in different degrees in rock failure and deformation.In order to study the acoustic signal characteristics of granite deformation,the acoustic emission and infrasound signals are combined to analyze,and the rock peak precursor characteristics based on them are proposed.Based on the waveform characteristic parameter discrimination method:the acoustic emission event rate appears relatively quiet period,the ring count reaches the second peak,the acoustic emission energy rate increases sharply to the maximum,and the fractal dimension value of infrasound energy rate decreases to the minimum.It can be considered that the rock is about to reach the peak stress.Based on the discrimination of main frequency parameters:the dominant frequency of acoustic emission is concentrated above 250kHz.,the proportion of dominant frequency of infrasound 0-5Hz and 15-20Hz decreases to the lowest,and the fractal dimension of dominant frequency of infrasound decreases to the lowest point.This series of characteristics can be used as a basis for joint discrimination of rock failure and improve the accuracy of discrimination.