Wavelet-Spectrogram Analysis of Surface Wave Technique for Quick NDT Measurement on Surface Layer of Pavement

Reliable assessment of in situ pavements stiffness is an important aspect in effectively managing a pavement system. The aim of this paper is to propose the new procedure, namely the wavelet-spectrogram of surface wave (WSSW) technique for non-destructively measurement of elastic modulus on surface layer of a pavement system. Using two receivers, surface wave propagation on pavement surface was recorded and transformed into in frequency domain by wavelet analysis. For this analysis, a derivative Gaussian wavelet was selected as an appropriate mother wavelet for seismic waveform propagating along pavement surface. Thus, an interactive 2-D plot of time-frequency spectrogram consisting of wave-energy spectrum was simultaneously generated. CWT-filtration method was implemented in order to reduce the effect of noisy signal recorded during measurement. From selected wave spectrogram, the unwrapped phase different spectrum was generated to obtain phase velocity which was performed by least-square linear regression. Finally, the elastic modulus of pavement surface layer was calculated from a modified relationship between phase velocity, Poisson ratio and density of pavement surface layer. The results show that the proposed technique is able to measure in situ elastic stiffness of the surface layer. In addition, the change of the surface layer stiffness is also able to be monitored. The stiffness (elastic modulus) produced by the WSSW technique is classified as a modulus at very low strain level.