Application of Wavelets in Detection of Cavities under Pavements by Surface Waves

A new seismic approach based on wavelet transforms of the surface response is proposed and applied to the problem of detection of shallow cavities under pavements. Seismic wave propagation is simulated by a transient response analysis on an axisymmetric finite element model. Shallow cavities in a homogeneous half-space and a pavement system of a variety of shapes and embedment depths are considered. The formulation of the continuous wavelet transform (CWT) is presented and its advantage over the traditional time or spectral analysis based methods is demonstrated through illustrative examples. The response of the medium at different surface points is presented in the wavelet based time-frequency maps. Waves reflected from the boundaries of a cavity introduce new features of specific time and frequency characteristics in the wavelet time-frequency maps. The characteristics of these features can be used to locate a cavity and estimate its size. As a case history, detection of a cavity/sinkhole under the pavement of a section of expressway I-80 in the northwestern New Jersey is presented