Effective techniques for a nondestructive evaluation of mechanically stabilized earth (MSE) walls during normal operation or immediately after an earthquake event are yet to be developed. MSE walls often have a rough surface finishing for the purpose of decoration and are reinforced with both horizontal and vertical steel bars. Two wide-band microwave inspection approaches were investigated for detecting and evaluating characteristics of materials behind an MSE wall section. The first approach used spot measurements with a wide-band frequency-modulated continuous wave (FM-CW) radar system. While effective to penetrate through mortar blocks in the laboratory, the radar system was found to have limited applications in MSE walls due to its thick layer, material heterogeneity, surface roughness, and the presence of steel bars. The second approach took wide-band measurements on a two-dimensional (2D) grid and produced three-dimensional (3D) images using a synthetic aperture radar algorithm. Imaging allows for signal averaging and relatively easy distinction of localized features such as steel bars from undesired flaws. Two-dimensional slice images at the location of the anomalies were produced. Several different anomalies placed behind the wall can be detected, demonstrating the effectiveness of the imaging technique as a potential approach for back-fill soil inspection (e.g., moisture, void) behind an MSE wall.


Electrical and Computer Engineering

Second Department

Civil, Architectural and Environmental Engineering


Research and Innovative Technology Administration (RITA)

Report Number


Document Type

Technical Report

Document Version

Final Version

File Type





© 2014 Mid-America Transportation Center, All rights reserved.

Publication Date

01 Jun 2014