Research On Road Crack Detection Method Based On The Principle Of Rayleigh Wave

Based on the propagation characteristics of Rayleigh waves in the crack,methods to detect the surface crack and the internal crack are proposed.The detection targets of surface cracks include the depth,length and angle of surface cracks.The surface crack depth refers to the vertical distance between the tip of the surface crack and the surface of the medium.Surface crack length refers to the distance between the upper tip and lower tip of the surface crack.The angle of surafce crack refers to the angle between the surface crack and the horizontal plane.The detection targets of the internal crack include the depth of the tip of the internal crack and the horizontal position of internal crack,where the depth of the internal crack refers to vertical distance between the top tip of the internal crack and the surface of the medium,and the horizontal position of the internal crack refers to the horizontal position of the top tip of the internal crack.The research work in the paper is divided into the numerical simulation module and the test verification module.In the numerical simulation module,the two-dimensional road model is established.The seismic source and receiving points are set on the surface of the model.The seismic source is used to apply impulse load and the receiving point is used to detect the stress wave.In the test verification part,the reliability and rationality of the detection method of the surface crack depth is verified through field test.When studying the detection method of surface crack depth,the depth of the surface crack is divided by the wavelength of the Rayleigh wave to obtain the normalized depth of the surface crack.It is found that there is a fixed realtionship between the energy transfer coefficient and the normalized depth of the surface crack.The center frequency of Rayleigh wave and the depth of the surface crack have no influence on the relationship.Based on the fixed relationship,the relationship curve of the energy transfer coefficient can be obtained.When the energy transfer coefficient Tr is larger than 0.1 obtained in the field test,the depth of the surface crack ds can be calculated according to the curve.When studying the detection method of the length of the surface crack,based on the propagation characteristics of Rayleigh wave at surface cracks,it is found that the propagation time and the propagation speed of Rayleigh wave on the left and right sides of the surface crack can be used to calculated the length of the surface crack Ls.The error percentage between the surface crack length calculated according to this method and the actual length of the crack is generally less than 10%.When studying the method of detecting the angle of the surface crack,based on the propagation characteristics of Rayleigh wave at the surface crack,it is found that the propagation time of the diffracted longitudinal wave from the lower tip of surface crack to the receiving point and the propagation speed of the diffracted longitudinal wave can be used to calculate the distance between the lower tip of surface crack and the receiving point.Knowing the distance between the upper right corner of surface crack and the receiving point,the length of surface crack,and the distance between the lower tip of surface crack and receing point,the angle of surface crack can be calculated.The error percentage of the calculated value of the crack angle is generally within 15%.When studying the depth of the internal crack,the depth of the internal crack is divided by the wavelength of Rayleigh to get the normalized depth of the internal crack.It is found that there is a fixed relationship between the eneygy transfer coefficient and the normalized depth of internal crack.The relationship has nothing to do with the center frequency of Rayleigh wave and the depth of the internal crack.Based on this relationship,the relationship curve of the energy transfer coefficient of the internal crack can be obtained.When the energy transfer coefficient Tr is smaller than 0.8 on site,the depth of the internal crack can be calculated according to the curve.When studying the horizontal position of the internal crack,based on the reflection phenomenon of Rayleigh wave at the internal crack,the time difference between the reflected Rayleigh wave and incident Rayleigh wave passing through the receiving point and the propagation speed of Rayleigh wave can be used to calculate the horizontal distance between the upper tip of the internal crack and the receiving point.The error percentage of the calculated distance is within 10%.At the same time,it is found that the angle of the internal crack will affect the accuracy of the calculated results.When the angle of the internal crack is 90°,the calculation accuracy is the highest.As the diviation from 90° increases,the error percentage gradually increases.In addition to numerical simulation,the field test is also carried out to verify the reliability and rationality of the surface crack detection method.According to the proposed method,the depth of the surface crack can be calculated,and the error between the calculated depth and the actual depth is about 20%.