Investigation of ground cavity using ground penetrating radar

As cavities in the ground may cause severe settling and sinkholes, an accurate investigation of ground cavities is essential. Recently, the use of ground penetrating radar (GPR) has actively increased because the GPR survey allows the investigation of a wide area within a short time. However, an error can occur in the results of the GPR survey because the GPR survey produces only the interface between layers with different electromagnetic impedances. In this study, the characteristics of the electromagnetic wave reflected from the ground cavity were experimentally identified. To artificially create a cavity, a frozen carbon dioxide cube was buried in a ground specimen and sublimated, and endoscopic images were then taken to make sure the artificially created cavity was maintained. The GPR survey was conducted on the ground specimen at a survey distance of 2 m. As a result, the cavity was observed at the location where the frozen carbon dioxide was buried. In addition, the result of the GPR survey shows that the polarity of the electromagnetic wave reflected from the cavity is the reverse of the polarity from the first strong signal. The characteristic of the reflected electromagnetic wave identified in this study may be effectively used for investigation of ground cavities.