Using Electromagnetic Waves to Detect Subsurface Voids

Detecting the presence and extent of subsurface voids under a roadway structure is critical in preventing major disasters from occurring. In this study, a 400MHz ground coupled penetrating radar (GCPR) was utilized in two projects to locate voids. The air voids present a strong negative dielectric contrast to electromagnetic waves and, therefore, these anomalies are clearly identified on GCPR results/plots. Two case studies were presented in this paper. Electromagnetic waves were able to locate subsurface voids under the continuously reinforced concrete pavements. Fortunately, those subsurface voids have been identified before severe roadway failure occurred. Otherwise, those voids could have grown in size until the roadway eventually collapsed.