Study On Correction Of Kaiser Point And Floating Threshold Of Rock Acoustic Emission Based On Wavelet Analysis

It has already become an essential topic that how to measure the ground stress accurately due to the requirement of mining,water conservancy and hydro-power project,civil construction,railway,highway and other projects.During the past decades,on the one hand,mining,underground engineering and other projects require a deeper depth into the ground,on the other hand,the surroundings of the underground construction is becoming more and more complicated,which has raised a great challenge to the conditional and native measurement of the ground stress.So,many scholars have begun to research an method of native sampling and evaluating at laboratory in another way.The method of measuring the ground stress by Kaiser Effect of rock acoustic emission has drawn the public attention because it's economy,convenient and the development potential.However,many problems have not been solved properly in the practice of using the Kaiser effect to measure the native ground stress,which hindered the spreading of it.One of the most prominent problems is that whether Kaiser Point can indicate the ground stress correctly.Research shows that the experimental Kaiser Point would be inaccurate due to the experiment itself,and the inconspicuous accumulated energy curve inflection point.The accuracy of Kaiser Point not only directly affects the effect of rock acoustic emission experiment,but also have an influence on the promotion of the technology.The domestic and foreign scholars have done a lot of research work on the Kaiser Point problem of rock acoustic emission,most of which are based on the analysis of parameters.For example,an acoustic emission pulse corresponds to an acoustic emission counts(the pulse signal exceeds the system's threshold),while the information contained in the signal itself is often ignored.In this thesis,technology core is the idea of analyzing waveform by analyzing signal characteristics of the Kaiser Point or other special points,and judge the experiment Kaiser Point and correct the pseudo Kaiser Point,and discussed the rock floating threshold of acoustic emission experiment based on waveform analysis in the end.The main work and conclusions are as following:(1)The rock acoustic experimentThe test samples are all sandstone which are selected from a mine in Zhongliang Mountain,Chongqing,and are divided into 3 groups: superficial layer 70m-130m;middle layer 130m-230m;deep layer 230m-440 m.Using acoustic system PCI-2 to conduct.It uses totally 282 groups of samples(select 60 group of sample)to get the sample evidence by conducting conventional acoustic emission test,cyclic loading test and verification test.(2)Construct the special wavelet basis function of rock acoustic emission signal.Select the second-order weakly damped vibration unit pulse function which is similar to the acoustic emission raw signal of the rock as the basic function of the wavelet constructor.It is proposed that the constructive function must be build up of the three tectonic conditions which are non-periodic,consisting of a number of different vibration functions with different amplitudes,with abrupt signals and rapid decay.And finally,the wavelet basis function is constructed based on the characteristics of rock acoustic emission signals by demonstration.Through verification,the constructor is superior to the common wavelet basis function from the comparison of the similarity of the original acoustic emission signal,the integrity of the signal reservation,and the practical meaning of the parameter.(3)Study on energy characteristics of acoustic emission Kaiser point instantaneous signal frequency bandCarry a series of conventional acoustic emission test on the samples.Firstly,find out the Kaiser points of each sample,and calculate the general stress state by contrasting theory.Secondly,decompose the Kaiser point instantaneous signal of all rock samples into three-level wavelet packets.Then analyze the energy of Kaiser point signal in each sample.Finally,the conclusion comes that the low frequency energy of the rock acoustic emission signal below 937.5kHz accounts for the vast majority of the energy of the signal,and the energy of the real Kaiser point band mainly concentrates in the frequency range of 0 ~ 312.50 kHz,while the energy of the non-Kaiser point signal accords with the most concentrated In the 937.5kHz low frequency,but in 0 ~ 312.50 kHz frequency does not account for most of the energy in total.(4)Study on Kaiser point offset correctionThe test results show that the Kaiser point may have a large deviation.The relationship is ascertained between energy and amplitude,energy and acoustic emission ring count,energy E and stress state of the acoustic emission signal,and the experimental Kaiser point error correction function is obtained in the end.The modified Kaiser point is decomposed into three layers to determine the energy characteristics of the frequency band by using the modified function and taking the test samples as an example,respectively.(5)The study of the cumulative energy curve of acoustic emission which has no inflection pointBased on the analysis of the smoothness of the energy curve,this article proposes that the Kaiser point research is based on the large crack in the "high stress" state.The relationship between the crack release energy and the crack stress intensity factor is derived from the relationship between the crack stress intensity factor and the stress.And finally it is concluded that the strain energy releases outwardly,and the greater the stress intensity factory is,the greater the rate of crack energy releases.(6)Floating Threshold of Rock Acoustic Emission TestIn order to obtain the low energy point signal,this paper obtains the float threshold formula based on the double threshold test design.Besides,it establishes the relationship between the change threshold and the load.Compared with the fixed threshold system,we find that it can correctly reflect the Kaiser point signal by using the floating threshold formula to reduce the noise of the sample,and at the same time,there is a high signal retention at low energy and low energy distribution frequencies.From the standpoint of signal retention,it is superior to the conventional fixed threshold(a reasonable fixed threshold is accurate for analyzing high energy points such as Kaiser points).