Study On Quality Inspection Of Cement-soil Mixing Pile By Rayleigh Wave Test

There are various kinds of soft soil layers in the vast area of China,which are formed by different causes.Cement-soil mixing piles can maximize the use of the original soil and are always used as common methods to reinforce the soft foundation.At present,the ways adopted to test the quality of cement-soil mixing piles are usually destructive testing,such as drilling core,standard penetration,static load test,etc.,which will cause damage to the tested mixing piles and meanwhile have the shortcomings of high labor intensity,high cost and slow speed.Therefore,this paper studies the technical principle and working method of non-destructive testing of cement-soil mixing pile quality by transient Rayleigh wave method,and carries out engineering application based on the widening project of Lian-Huo Expressway.The main contents of this paper are as follows:(1)Through the method of combination vibroseises and multiple stacking to suppress random noises,the quality of field data acquisition is improved.The Rayleigh wave is extracted in both the spatial-temporal domain and the τ-p domain to satisfy the calculation requirements of the adjacent-channel dispersion curve and the curve is then calculated by changing frequency interval method to improve the imaging ability of Rayleigh waves in the longitudinal low frequency band.Combining Rayleigh wave velocity with pile quality and bearing capacity,a set of practical non-destructive testing methods of cement-soil mixing piles by transient Rayleigh wave is formed,which improves the detection level of concealed engineering.(2)The main techniques of non-destructive testing method of pile foundation by Rayleigh wave are analyzed.The random interference waves are suppressed by combining different offset and multiple stacking methods and Rayleigh wave is extracted by τ-p transform to improve its lateral resolution.By calculating the adjacent-channel dispersion curves,the imaging ability of deep targets could be effectively improved.Through actual calibration,analysis and calculation,the relevant influencing factors are obtained to further improve the accuracy of non-destructive testing methods and achieve the transformation of non-destructive testing from qualitative to quantitative.(3)The application of transient Rayleigh wave method to the quality testing of cement-soil mixing piles has made the testing non-destructive and shortened the testing period(core drilling usually needs to be carried out after 28 days,and the testing period of the method in this paper is 7 days),which is meaningful for speeding up the construction progress.Therefore,transient Rayleigh wave method for testing cement-soil mixing piles can achieve non-destructive testing,improve detection efficiency,shorten detection cycle,and achieve qualitative and quantitative evaluation,which is of great significance.