Application of GPR technique for subsurface utility mapping: A case study from urban area of Holy Mecca, Saudi Arabia

Subsurface utility mapping is an important technique for extracting subsurface information about buried utilities such as electric and telephone cables, water and sewage pipes and other infrastructure, particularly in the dense urban areas. Since the Holy Mecca city has many engineering development projects that need geotechnical excavation procedures across a wide inhabited area, there is a great demand for locating and imaging the subsurface utilities before starting the excavation process, particularly whereas there is no available information about the location of subsurface utilities. In this study, a 400 MHz antenna was utilized to map and identify the possible subsurface utilities along the investigated site. The survey was carried out along an asphalt road, roughly perpendicular to the expected direction of the utility infrastructure. Most of the subsurface features consisted of different pipes, cables, shafts, sharp interfaces between the filling and the original soil, sewage and flooding sewers. From the consistent character of the hyperbolic reflected signals along the successive profiles, it was possible to trace pipe lines, cables and vertical shafts. The results of this study highlight the importance of carrying out geophysical surveys before the excavation process particularly in the crowded urban sites, where the misdetection of any of the subsurface utilities may be hazardous.