불발탄(UXO) 조사를 위한 지하투과레이다(GPR) 적용 사례

Abstract

During excavation at construction site in downtown of Seoul, 2 Unexploded Ordnances (UXO) were detected. To ensure the safety of following works, high-resolution geological investigation for detecting UXO was to be required. Considering the site condition, the top side was covered by deck plate and steel beams were installed up to the depth of 20 m with 4-6 m spacing, GPR (Ground Penetrating Radar) was chosen as the most applicable investigation method among magnetic survey, EM survey and GPR. The survey was carried out with grid of 0.5 m spacing by using 500 MHz shielded antenna (RAMAC) and repeated three times after digging up the ground every 1 m which was the reliable depth with GPR. Prior to the survey, GPR signal patterns of UXO were defined by modeling test. Anomaly signals of the results are classified as 3 degrees. The object doubted as UXO is defiend as 1st degree. The 2nd degree indicates small things like minor metals and other weak signals are classed as 3rd degree. From the GPR investigation, although a lot of small anomalies of the 2nd and 3rd degree were detected, the 1st degree signal was not detected. Through partial digging, some signals were identified as the geological structure zone and the multiplicity of reclamation material such as small metal bodies, masonry and boulder. Therefore, it is required to distinguish geological signals from other signals by understanding the site geology and the geologic formation prior to the survey in order to get more accurate information corresponding to survey purpose.