Non-Metallic Line Locating



GPR has the unique ability to locate and image non-metallic targets in the subsurface like PVC, clay or brick pipes, and concrete pipes. These types of utilities are much more difficult to locate with conventional methods creating a specific use for GPR technology. Unlike other utility mapping, GPR compares and contrasts subsurface materials through differences in dielectrical
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constants of individual components; making objects appear in an otherwise homogeneous medium. This is the basis of why GPR can detect these targets in the subsurface.

It has been our experience that many non-metallic utilities in this area of expansive surficial clays have a tendency to “move” during periods of excessive inundation or drought. As this tendency is a function of clay minerals at the molecular level to “bind” interlayer water through ionic bonding. The cyclical behavior of the material eventually creates weaknesses along the line making failure imminent. In one application we were contracted to locate a suspected 4 inch PVC septic line extending through a proposed expansion at a county hospital. Due to the untimely death of the one man possessing the ONLY copy of the actual blueprints of the line when installed many years ago the hospital had no inclination of knowing where this line was.

Working cooperatively with our client TeaCo successfully located the septic line for our client and provided a cross sectional image of this structure in the subsurface along with the appropriate GPS coordinates. The combination of placing marking paint on the ground and a permanently georeferenced plan map of this utility in the subsurface was critical in the immediate expansion efforts at this facility. This graphical image provided insight to engineers concerning the hydraulic environment for discharge. The interpreted georeferenced cross section was imported as CSV into Surfer®, and then into a GIS program and made into a layer that is still in use today.

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