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Microwave Synthetic Aperture Radar Imaging for Nondestructive Evaluation of Mechanically Stabilized Earth Walls

Mechanically stabilized earth (MSE) walls are advantageous over gravity and cantilever retaining walls in terms of cost effectiveness, construction time, and tolerance to differential settlement. However, voids and moisture changes behind mechanically stabilized earth walls have previously led to distress and failure, and effective nondestructive evaluation tools for their detection are yet to be developed. In this study, a wideband (1–4 GHz) microwave synthetic aperture radar imaging technique was employed to generate 2D slice images of a mechanically stabilized earth wall system at various depths. Two 1.52 × 1.46 × 0.178 m reinforced concrete wall panels with backfill sand were investigated. The effects of surface roughness, voids, and moisture change were investigated. The effect of change in moisture content behind the wall and in a 350 × 250 × 76 mm sandbox was clearly detected. Two foam blocks to simulate voids, measuring 127 × 127 × 51 mm and 254 × 254 × 51 mm, respectively, were also successfully located and imaged. The proposed and implemented imaging technique was proven to be robust and a promising technique for detecting voids and moisture changes behind MSE walls.

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