How Utility Mapping Can Complement Ground Penetrating Radar (GPR)

Ground Penetrating Radar (GPR) is one of the crucial tools in the Subsurface Utility Engineering toolbox, helping locators detect subsurface utilities non-intrusively. Because the effectiveness of GPR technologies can vary depending on subsurface conditions, remote utility mapping can be a key tool in advance of and alongside GPR scanning to help overcome challenging subsurface environments.

In this post, we’ll touch on the following points;

  • What is Ground Penetrating Radar (GPR)?
  • Why does GPR effectiveness vary from state to state?
  • How can remote utility mapping complement GPR efforts?

What is Ground Penetrating Radar (GPR)?

Ground Penetrating Radar (GPR) is a non-destructive tool that can be used to image the subsurface. Simply put, GPR works by transmitting electromagnetic waves, and receiving the reflected signals as they detect discontinuities. GPR systems can be operated by hand in the field, and sometimes are towed on various vehicle platforms.

Because it can often effectively detect many subsurface objects, GPR is one of the main tools that Subsurface Utility Engineering engineers choose to integrate into their locating projects. In some municipalities in Texas, for example, using some form of GPR is even a legal requirement before beginning the construction phase of a project.

While GPR is a crucial tool and an essential element for many Subsurface Utility Engineering (SUE) projects, it’s not perfect for all situations and all project areas. In particular, GPR can be a less effective tool in states with challenging soil conditions–especially Texas.

Why can GPR effectiveness vary from state to state? 

As mentioned, Ground Penetrating Radar relies on electric signals that are sent and received through the soil. For that reason, the soil conditions of a given project site can have a major effect on the efficacy of GPR as a tool for finding subsurface utilities. 

The National Resources Conservation Service (NRCS) provides suitability scores for GPR use nationwide. They rank the effectiveness of GPR depending on many factors, most notably the soil types. In particular,  the clay content, salinity and sodicity, and the levels of various minerals in the soil can all influence the suitability of GPR in a given project site. 

GPR is particularly effective in sandy and gravelly soils, where penetration depths can reach up to 160 meters. However, in soils with higher clay concentrations, GPR becomes less effective, as electromagnetic signals have more difficulty penetrating the soil. The NRCS suggests that soils with ‘more than 35 percent clay are restrictive, soils with less than 10 percent clay are generally favorable to deep penetration with GPR.”

Source: US Department of Agriculture, National Resources Conservation Service, Ground Penetrating Radar Suitability Maps.

In states like Florida and in much of the Northeast, where soil conditions are more suitable, GPR can be quite an effective tool. In states like Texas with very clay-rich soils, GPR can be less effective as a tool for identifying subsurface utilities. In Texas in particular, large swaths of the state can be especially challenging for GPR methods, because soil conditions interfere with electromagnetic signal penetration.

Source: US Department of Agriculture, National Resources Conservation Service, Ground Penetrating Radar Suitability Maps.

For that reason, project managers and SUE experts often need to turn to other methods to identify subsurface utilities, including electromagnetic locating, metal detectors, and sometimes vacuum excavations. Each of these methods have their own advantages–and disadvantages.

How can remote utility mapping complement existing GPR methods?

Remote utility mapping that is based on visual analysis can address many of the potential shortcomings of GPR, giving all stakeholders a clearer picture of the subsurface landscape. 

Because remote utility mapping relies on visual evidence from satellite and aerial imagery, it can often establish the location of subsurface utilities regardless of different soil types and varying subsurface conditions. And because it is remote, it can provide a preliminary—and large-scale–understanding of the subsurface well before boots-on-the-ground locators begin work in the field.

Utility mapping can give Subsurface Utility Engineering experts a roadmap to guide their efforts, helping them resolve differences between as-builts and real world conditions. It can also help them designate subsurface utilities more precisely, cutting down on wasted time and effort boring for utilities in the wrong location. In addition, utility mapping provides quality assurance for locators out in the field, who can be more confident that they haven’t missed an unregistered or abandoned utility that didn’t appear on the as-built records.

Ultimately, utility mapping can be a crucial element in the SUE engineer’s toolbox, giving a clear large-scale look at the project area and giving engineers confidence about subsurface conditions before heading out to the field.

Interested in seeing how utility mapping can complement your designating and locating work? Contact us!

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