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Deterioration of underground structures such as pipelines and culverts are very difficult to be detected in the early stage. Yet, their failures can cause significant damages to the above roadway and adjacent superstructures. However, detecting the development of deterioration in underground culverts is a challenging task. For example, development of an underground void or sink hole can cause stress redistribution in the vicinity of a culvert and potentially damage the culvert. In this paper, we present our research work on the use of a dual-frequency (300MHZ and 800MHZ) ground penetrating radar (GPR) system (UtilityScan, GSSI) for detecting the growth of an artificial void in a layered culvert structure. A laboratory three-layer (asphalt layer, gravel sub-base layer, and subgrade layer) setup with an underground air void and a 30” diameter culvert was manufactured as a testbed. Three different levels of damage were artificially created inside the laboratory setup and inspected by the GPR system on surface layer. From our experimental result, it is found that the wavelength of 300MHz GPR signal is not sensitive enough to image the growth of an underground void inside the experimental setup. On the other hand, the wavelength of 800 MHz GPR signal can reconstruct the growth of the underground void. This research work indicates the advantage of multiple frequencies for GPR subsurface sensing.
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