The effects of back scattering from a defect zone on guided wave dispersion in coast dykes

Abstract

In terms of seeking the characteristics of wave propagation many engineering infrastructures can be regarded as a waveguide due to their distinguished physical properties in contrast with the natural surroundings. Coastal protection dykes can be treated as such a waveguide. Taking this as the conceptual model we try to seek the signature of the voids or defect weak spots inside the dyke or in the underlying formations on the guided elastic and electromagnetic waves. We studied the effects by first looking into numerical simulations. The numerical tool is the finite difference time domain (FDTD) method. We simulated both the elastic wave in two-dimensional P-Sv fashion and the electromagnetic (EM) wave in TMz mode. Simulations of the elastic wave in P-Sv fashion is for mimicking the propagation of the seismic Rayleigh wave in the waveguide; whereas simulations of the TMz mode is for mimicking the propagation of the ground penetrating radar (GPR) wave in the waveguide defined by the dyke. Given the commonly used geophysical tools for engineering non-destructive testing and evaluation (NDTE while the target defect zone size is also at meter scale with a depth of up to 10 meters. Preliminary results in numerical simulations suggest that significant feature changes can be generated by the existence of the defects. The simulation results are validated by field observations with known exist defect zone in a segment of the costal dyke.