Mystery Solved – The “Non-Locatable” Pipe Located | Subsurface Imaging Mystery Solved – The “Non-Locatable” Pipe Located | Subsurface Imaging
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Mystery Solved – The “Non-Locatable” Pipe Located
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t’s no secret that there is a tremendous amount of infrastructure buried under our feet. Knowing where services are located is an ongoing challenge given the rapid rate at which installations are taking place.

Ground Penetrating Radar (GPR) is a proven, cost-effective solution to help locate buried utilities. GPR excels at locating not only metallic but also nonmetallic utilities that cannot be found using traditional electromagnetic (EM) methods; these utilities are often referred to as “non-locatables.”

For years a building manager at a company headquarters in Germany had known that a water pipe was running into their facility but had not been able to locate its exact whereabouts.

Locators using traditional EM technology tracked the pipe to a certain point where it then appeared to end abruptly. A valve had reportedly been installed to allow for the pipe to be drained; however, none of the locators could find it. They concluded that the original contractor had switched from metal pipe to PVC pipe during the installation. Since EM technology relies on objects being metal to trace them, the PVC section of pipe was not locatable. The building manager recognized that it was a maintenance concern and made one final effort to locate the pipe and valve by calling in a GPR expert.

The contractor used an LMX200™ GPR system for this project. As the operators were surveying the area with the GPR (Figure 1), they encountered several different utilities, each appearing as the classic hyperbolic-shaped GPR response. To ensure they were indeed tracking the water pipe, they moved to the area where the pipe was found using EM methods and crossed it using GPR. On the screen, they noted the depth of the pipe and how the hyperbola appeared in the GPR data. They proceeded to search the area, focusing on responses at that approximate depth, and for hyperbolas that looked similar.

LMX200™ GPR – designed specifically to make marking utilities with GPR simple and easy
Figure 1:
When utilities can not be located through traditional means, locating professionals bring in the LMX200™
to get the job done.

Data was collected in a zig-zag pattern crossing over the buried pipe (Figure 2), with lines about 1 meter apart. As the pipe was identified in the data, the locations were marked on the ground using flags. The path of the pipe was determined by “connecting these dots.”

Survey path of the GPR as it crossed the pipe.
Figure 2:
Survey path of the GPR as it crossed the pipe.

The Line Scan data is shown in Figure 3. Each image is a traverse crossing the pipe at 90 degrees.

Each crossing of the pipe shows two hyperbolic responses, aligned vertically. This indicates the pipe is non-metallic.
Figure 3:
Each crossing of the pipe shows two hyperbolic responses, aligned vertically. This indicates the pipe is non-metallic.

There are some features worth noting in the data:

  • The pipe is at approximately 1m (3.2') deep.
  • There are two hyperbolas, one above the other. The top hyperbola is caused by the GPR reflection from the top of the plastic pipe; the lower one is from the bottom of the plastic pipe. (Note that the bottom of the pipe is clearly visible because the pipe is non-metallic and water-filled creating a distinct pipe bottom response).

After tracking the pipe with the GPR, the LMX200™ arrived at the valve and showed exactly where they needed to excavate.

The LMX200™ located the buried water valve, which was subsequently uncovered to drain the pipe.
Figure 4:
The LMX200™ located the buried water valve, which was subsequently uncovered to drain the pipe.

GPR was able to successfully locate and map the entire path of the water pipe, both the metallic and the PVC sections, right to the buried water valve lid, enabling them to drain the water pipe.

The building manager was pleased to have located the route of the pipe and the position of the valve. The LMX200™ provided valuable information to allow for scheduled maintenance on the pipe and to ensure this pipe is avoided during future upgrades to the facility.

Click here to learn more about LMX200™ Ground Penetrating Radar.

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