Study On Vibration Characteristics And Failure Criteria Of Soft Rock Under Loading Based On Laser Vibration Measurement Technology

Rock failure and instability is the root cause of engineering disasters.It is of great theoretical research value and engineering application significance to predict rock failure and instability effectively.In this paper,acoustic emission technology and non-contact laser vibration measurement technology are used as research means to carry out compression and splitting tests of marble and sandstone with different integrity and different test positions.Based on the test data,the characteristics of acoustic emission signal and laser vibration measurement signal of soft rock under different working conditions are summarized,and the variation range of acoustic emission parameters and laser vibration measurement parameters under loading is quantified.In contrast with the acoustic emission technology,the damage criterion of soft rock under loading based on laser vibration measurement technology is established.According to the different deformation stages of rock,the oscillogram of laser vibration measurement is divided into three stages: elastic stage,plastic stage and failure stage,and each stage is divided into wave stage and static stage.The paper studies the method of three stages and six stages The contents and achievements are as follows:(1)Under compression test.The failure mode of the specimen is compression shear failure,and the specimen with prefabricated cracks is relatively rare after failure.The characteristics of acoustic emission signal and laser vibration signal under compression have obvious corresponding relationship.The characteristics of AE are as follows: there are AE events in the early stage of loading,the AE parameters increase abruptly when the AE is damaged,and the high frequency signals in AE spectrum concentrate.Before fracture,AE parameters of the cracked specimen increased sharply in a short time until the failure reached the maximum.The AE spectrum was concentrated around 100 k Hz,and the distribution of 35 k Hz low frequency band was obvious.The vibration signal of laser vibration measurement is shown as follows: in the middle and pre loading period,the wave form appears alternating wave period and static period;when the sample is close to failure,the wave form appears unique and short wave period,and the frequency spectrum signal shows obvious frequency band distribution;in the static period,the main frequency amplitude of the signal increases,while the secondary frequency amplitude remains unchanged;when the sample is damaged,the wave form appears large vibration,The frequency spectrum is dominated by low frequency and high amplitude signals,and the amplitude of high frequency signals is also significantly increased.The maximum amplitude of the vibration signal of the cracked specimen is smaller than that of the intact specimen,and the main frequency of some specimens has a certain frequency shift phenomenon in the wave fluctuation period.(2)Under splitting test.The basic failure mode of the specimen is tension failure,and the main fracture surface is formed in the direction of parallel loading.The crack will obviously reduce the strength of the specimen(about 40% of the complete strength),and guide the development of the fracture surface.The characteristics of acoustic emission signal and laser vibration signal under Splitting have obvious corresponding relationship.The characteristics of acoustic emission are as follows: there is acoustic emission activity in the early stage of loading,and the whole process spectrum is concentrated in the low frequency band of 100 k Hz.When the loading is damaged,the acoustic emission parameters suddenly increase,especially the high frequency signals in the AE spectrum.The vibration signal of laser vibration measurement is characterized by alternating wave period and quiet period in the first and middle period of loading,but the wave in the initial period of loading is not as strong as that in compression test,and there is a short wave signal when the sample is damaged,and its frequency spectrum shows the frequency band distribution,and there is also a quiet period in the plastic phase after it is tight.When the sample is damaged,there is a large vibration in the waveform,and the frequency spectrum is distributed in low frequency and high amplitude,and the amplitude is relatively high In the early stage,the amplitude of high frequency signal increases 5-10 times.Under various working conditions,the vibration characteristics of laser vibration measurement are different.The specific performance is that the maximum velocity amplitude of sandstone waveform is greater than that of marble,sandstone is more concentrated than marble,the spectrum distribution of complete sample is more concentrated than that of cracked sample,and the maximum velocity amplitude of cracked sample is greater than that of complete sample when it is damaged.There is a long period of calm in the early stage of test waveform of cracked sample tip,and the frequency of each stage is higher Amplitude lower than side test.(3)Through comparative analysis,it is found that there is a strong corresponding relationship between the change of vibration signal of laser vibration measurement and the change of acoustic emission parameters.That is to say,in the stage of obvious change of acoustic emission parameters,the wave form of laser vibration measurement also has a strong fluctuation change.At the same time,the trend of spectrum change of the two is basically the same,which shows that the low-frequency signal is the main part before and during the loading,and the high-frequency signal is strengthened when the loading is damaged,Compared with the acoustic emission technology,the failure criterion of soft rock under loading is established based on the wave parameters and spectrum characteristics of laser vibration measurement.