<title>Characterization of elastic wave propagation in soil</title>

Abstract

To optimize a landmine detection system currently being developed at Georgia Tech that uses both electromagnetic and elastic waves, wave propagation in soils has been studied to evaluate propagation characteristics and to identify nonlinear mechanisms. The system under development generates elastic waves in the soil using a surface-contacting transducer designed to preferentially excite Rayleigh waves, thus interrogating the surface layers of the soil. These waves propagate through the region of interest and interact with buried landmines and typical clutter objects (i.e., rocks, sticks, and man-made objects). Surface displacements are measured using a non-contact radar sensor that is scanned over the region of interest. To characterize the wave propagation effects as a function of drive amplitude and as a function of input signal type, a series of experiments was conducted using the radar sensor, accelerometers, and geophones at two test sites, the experimental model at Georgia Tech and a field test site at the Georgia Tech Research Institute's Cobb County Research Facility in suburban Atlanta. The two test sites presented different soils as the experimental model uses damp, compacted sand as a soil surrogate while the field test site has a well-weathered mixture of sand, silt, and clay. Surface displacement measurements were made using the radar sensor while both surface and subsurface measurements were made using triaxial accelerometers and geophones. Linear and nonlinear dispersion, wave speed changes, and nonlinear saturation were observed in the measured data.