Research On Quality Detection Of Tunnel Bolt Based On Ultrasonic Guided Wave Method

Bolt anchorage technology is widely used in tunnel engineering,the anchorage quality,such as anchoring length and density,are related to the safety of tunnel structure,and existing detection methods have some limitations.The ultrasonic guided wave has a good effect on the rod detection,so it is very suitable for the anchorage quality testing.However,in the present research results,the influence factors of the propagation characteristics are not close to the reality,the data analysis method is difficult to meet the detection requirements.Therefore,it is of great significance for the practical application of guided waves to study the influence factors and analytical methods.In this paper,we have studied the detection of anchor length and anchorage compactness of guided wave,analyze the propagation velocity and attenuation under various influencing factors,propose new techniques of guided wave signal processing,and constructs a novel nondestructive testing method for tunnel anchorage quality based on ultrasonic guided wave.The main research contents and conclusions are as follows:The comparison shows that the smoothing pseudo Wigner-ville distribution energy method has high computational accuracy and can immune the interference of noise to some extent.Field test results show that: the anchoring state and anchorage length have no effect on the speed of the guided wave propagation;guided wave velocities is different in different types of anchors.According to the time and velocity of guided wave propagation,the length and position of the bolt are calculated,and the error of the calculated result is less than 5%.The precision of threaded hollow anchors and threaded bar anchors is very high,but the accuracy of smooth bar anchors is decreased.The practical application shows that the wavelet threshold denoising method based on empirical mode decomposition can effectively improve the signal-to-noise ratio of the guided wave signal,while preserving the signal energy and waveform information.After studying the attenuation characteristics of the noise-reduced signal,it is found that the higher the acoustic impedance and the compactness of anchoring medium,the more serious the attenuation of guided wave is,and the attenuation degree of guided wave is different in different types of anchors.The attenuation coefficient is linearly related to anchorage compactness.The relationship between them can be obtained by linear fitting.To some extent,the quantitative analysis of anchorage compactness is realized.