Multi-parameter Coupling Analysis Of Acoustic Emission In Different Rock Failure

The direct cause of rock engineering geological disasters in mine construction is the redistribution of rock gravity and tectonic residual stress during the mining process.The fundamental reason is that the internal damage of rock promote the growth and expansion of primary defects,eventually link up and break.Acoustic emission(AE)is a transient elastic wave generated when the internal structure of the rock changes,and its signal characteristics have a corresponding relationship with the evolution process of rock damage.It is an important method to study rock damage and failure.On the basis of the indoor uniaxial compression AE test on granite,sandstone,limestone and marble,the mechanical characteristics and AE information of the whole process of rock failure are obtained.In order to compare the commonness and difference of different rock damage evolution characteristics,the time domain parameter characteristics(RA-AF value,AE event rate,cumulative number of events,energy rate,cumulative energy)and frequency domain waveform characteristics(AE dominant frequency,secondary dominant frequency,amplitude,sub-frequency band energy ratio)of AE signals are analyzed,and the fractal characteristics of the AE signals time and frequency domain are studied by combining the fractal theory.Combined with AE signals time-frequency domain to explore the damage changes inside the rock,and further seek to judge the precursor characteristics of rock critical damage.The main research results are as follows:(1)By analyzing the distribution of RA and AF values of the four rock AE characteristic indicators,it is shown that the rock failure modes and crack types reflected by them conform to the objective reality,and are consistent with the rock failure morphology obtained from indoor uniaxial compression tests.(2)By coupling analyzing the distribution rules of AE time series parameters(AE event rate and cumulative number of events,AE energy rate and cumulative energy),the evolution characteristics of the activity and intensity of the four types of rock AE sources(internal defects in materials)are obtained.The comparative analysis shows that the time domain parameters such as AE event rate and energy rate will have obvious precursor characteristics before the rock is near the main failure.(3)On the basis of wavelet threshold denoising,the corresponding frequency spectrum analysis is performed on the AE frequency domain waveform using fast Fourier transform,wavelet packet transform and other methods.After the calculation through the statistical parameter analysis program independently developed based on MATLAB software platform,Indicating that the two-dimensional spectrum of the AE waveform shows a single-peak,doublepeak,or multi-peak characteristic.That is,the AE secondary dominant frequency characteristic is not a phenomenon common to all waveforms,and is only unique to some signals.Analysis of the extracted dominant frequency and secondary dominant frequency shows that evolution characteristics of the two are similar;Frequency domain parameters such as AE dominant frequency,amplitude,and sub-frequency band energy ratio will show obvious precursor characteristics before the rock approaches the main failure.(4)Based on the obtained AE time-domain parameters and frequency-domain parameters,combined with the fractal theory and using its G-P algorithm,calculate the correlation dimension D-value of the time-frequency domain parameters in different stress intervals.It is concluded that the correlation coefficient R-value between the linear regression equation and the original data is greater than 0.98,indicating that the time-frequency domain parameters have fractal characteristics.Rock fissure development state is a transition process from disorder to order.The point where the fractal dimension began to decline continuously was taken as a precursor feature of rock failure and instability.