Full-scale Experiments for Roadbed Cavity Detection with GPR

Abstract:

Past few decades, deterioration of the underground facilities such as sewage facilities has increased significantly with growing urban development in Korea. The old damaged sewage pipes or conduits have washed away the surrounding soils beneath the roadbed, causing underground cavities and eventual ground depressions or sinkholes in the urban areas. Therefore, the detection of the roadbed cavities is increasingly required to prevent property damage and loss of human lives for precautionary measures. 3-D GPR technique was applied to conduct the full-scale experiment for roadbed cavity detection. The physical experiment has employed the soil characteristics of silty sand soils. The experimental site is composed of physically simulated cavities (Styrofoam, ε_r = 1.03) with dome-shaped structure and concrete sewage conduit. The simulated cavities were installed at regular intervals in spatial distribution. The land surface of the site was not paved with asphalt concrete at the current stage of the experiments. The results of the GPR measurements over the experimental site show that the reflection patterns from the simulated cavities are hyperbolic returns typical to the point source in 2-D perspective. A closer inspection of 3-D GPR volume data has yielded more clear interpretation than 2-D GPR data regarding where the cavities are situated in space. However, in case sewage conduits adjacent to the cavities are present, they could mask the GPR signals from cavities, leading misinterpretations. Therefore, data processing procedures should be more appropriately applied compared to the data for linear target detections. It is strongly believed that 3-D high density GPR data could be usefully applied to the roadbed cavity detections in the experiments. This study is an ongoing project of KIGAM and more realistic environments of the underground conditions would be prepared for the future study.