Quantitative Analysis Of Shape Parameters And Position Of The Defects Based On Transient Rayleigh Wave Method

The existence of detects significantly affect the quality of underground engineering,so it is necessary to detect the existence of defects using geophysical methods.Compared with other detection methods,transient Rayleigh wave method has advantages of a simple operation,wide detection range and high efficiency.The fluctuation characteristics of Rayleigh wave in isotropic elastic half space is analyzed based on the elastic wave theory.The fluctuation characteristics of Rayleigh wave in the medium containing defects is analyzed using finite element method,study simultaneously the characteristics of the Rayleigh wave energy,time domain and spectrum,and a quantitative analytical method of shape parameters of defects is proposed.the main achievements and innovations are follows:(1)The formula of the horizontal position of defects is proposed based on the propagation time difference between the incident Rayleigh wave and the reflected Rayleigh wave,and which’s accuracy is verified by numerical model.The calculation error is less than 2%,and the error increases with the increase of the buried depth.The critical disturbance frequency method is proposed to define the depth of the defects based on that defect don’t affect Rayleigh wave as Rayleigh wave wavelength is less than the depth of the defect and not otherwise.The relative error of the simulation results is less than 10% and the calculation error is increased when there is a filler in the defect.The concept of energy attenuation rate is proposed.The quantitative relationship between the vertical size and the attenuation rate of Rayleigh wave is analyzed and the formula is obtained.The accuracy of the calculation method is verified by different case.(2)The results of testing square and circular defect using Rayleigh wave are less difference as there is same vertical size.The filler in the defect consumes the energy of Rayleigh wave and the spectrum changes.The depth of the defect can be obtained by method of Rayleigh wave.The propagation law of Rayleigh wave in the medium containing double defects in horizontal position,vertical position and oblique position is analyzed,and the distance of defects in horizontal position obtained base on propagation time difference of Reflected Rayleigh waves,the results have high accuracy.(3)Compared with the two-dimensional model,the numerical simulation results of the three-dimensional model are closer to the actual value,but the difference between the two is not significant.To reduce the calculation,the two-dimensional model can be used to study Rayleigh wave.