Abstract
The survey area was reclaimed approximately 100 years ago, and the historical records indicate the presence of buildings on multiple sites in the area. Even though these buildings have now been removed, it is important to locate the buried foundations and remnants so that construction can be planed to avoid any associated problems. A frequency domain electromagnetic method (EM method) was used to explore a subsurface structure to a depth of 5 m, allowing buried utilities discarded underground located in a large survey areas (360×190m). We measured along 3D survey lines with a total extent of approximately 10 km using the EM38 and EM31 instruments which can explore to a depth of 1.5 m and 5 m, respectively. We described two plan views calculated from the responses of in-phase and quad-phase. Four classes of buried utilities were defined according to the electromagnetic response: (1) small sized metal utilities at depths to a few tens centimeters, (2) large sized iron plates at depths to a few tens centimeters, (3) iron pipes at about 1 meter in depth, and (4) the foundations of buildings deeper than 2 meters. Based on these results, we located suitable excavation positions and attempted to remove the large buried utilities using a heavy industrial machine. We uncovered two iron plates (6×1.5 m) at a depth of 0.2 - 0.5 m as well as reinforced concrete foundations (23×2.5×0.35 m) at a depth of 2.6 m. Additionally, the electrical conductivity derived using the EM method was in good agreement with the electrical logging data conducted by penetration tests at 15 points in the survey area. The EM method was demonstrated to be effective in locating buried utilities and exploring geological structures to a depth of 5 m within a large survey area.
