Application of wavelets in detection of cavities under pavements by surface waves: Fid-Bau Portal

Application of wavelets in detection of cavities under pavements by surface waves

Shokouhi, P. / Gucunski, N. / Maher, A.

Surface-wave methods have shown potential for underground cavity detection. A numerical simulation by finite element method was used to investigate effects of shallow cavities on surface wave patterns. Continuous wavelet transform is introduced and Gaussian wavelets (gaus1) are chosen for the analysis. Changes in power spectral surfaces and time-frequency wavelet maps caused by cavities are used in the detection. It has been demonstrated that a shallow cavity causes reflections of surface waves towards the impact source. Interaction of incident and reflected waves right before the cavity, as well as wave induced by oscillations of the cavity, cause energy concentrations in power spectral plots. As such, they can be used to locate the cavity. The pattern of energy peaks can also be used to estimate the size of the cavity. Reflections of different waves from the cavity can be clearly identified in wavelet time-frequency maps for the response at a single receiver position. Both time and frequency signatures of surface wave reflections from near and far side of the cavity can be identified in wavelet maps. The time difference between two reflection peaks, as well as the corresponding frequency of the peaks, can be used to locate the cavity and to estimate its size. From the wavelet maps for different receiver locations it can be concluded that those observations are valid for receiver locations between source and the cavity close enough to the cavity In general, the wavelet transform can be utilized effectively to locate shallow cavities in both homogeneous half-space and pavement systems. Field implementation of this new approach will follow the same procedure, and will utilize the same equipment setup, as the SWOD technique (16). The practical implementation of the technique in detection and characterization of cavities is being evaluated at the moment in the soil bin of Rutgers University.