Producing an Accurate Utility Locate in Any Soil Type

No one tool can take on all utility locating challenges. Soil conditions play a factor in equipment effectiveness. Here’s a look at approaches to take whether you’re utilizing ground-penetrating radar or an electromagnetic locator.

Producing an Accurate Utility Locate in Any Soil Type

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Soil type plays a big role in contractors’ ability to accurately locate underground utilities in advance of an excavation job.

For example, ground-penetrating radar can produce hi-res images of any object underground, but if the conditions aren’t optimal for it, the tool can be rendered useless. Here’s an overview of basic soil types and the best approaches to take when locating utilities in them.

SAND

In sandy soil, ground-penetrating radar is the most effective tool. Its high-frequency radio waves are able to easily penetrate the surface to provide a clear picture belowground.

The opposite is true of electromagnetic locating equipment. Dry soil conditions can make it difficult to form a solid circuit, preventing the transmitter from properly inducing a signal onto a utility line. That doesn’t mean you should completely abandon such tools in sandy soil. It will just require some trial and error.

If you’re locating with one frequency and not getting a good, solid signal, you might want to try a different frequency. Or move the grounding device because perhaps the circuit is jumping on to some other things and the frequencies aren’t focusing in the right matter. Then, if you have ground-penetrating radar available to you, it can be used to confirm findings and fill in the gaps.

CLAY

More clay-like soils will produce better results for electromagnetic tools. But ground-penetrating radar units can struggle. If the soil is really clayey — or dense with some water like a shallow water table or a recent rain — those waves are going to have difficulty penetrating through the soil.

Overcoming that obstacle can be as simple as waiting. If the ground-penetrating radar unit is deployed in the morning and not working very well, put it away and try again later in the day when soil conditions may be drier.

Changing out the antenna on a ground-penetrating radar unit for one with a higher frequency can also help in clay soils, especially when you just want to improve visibility and aren’t necessarily worried about penetrating as deeply into the ground. A typical ground-penetrating radar unit runs at 250 megahertz. In clay soils, switching to a 500 megahertz antenna might work better.

ROCK

For electromagnetic tools, the same methods employed in sand and clay should be used in rocky soil conditions — experiment with frequencies and the location of the grounding device.

But with ground-penetrating radar, it’s possible to confuse utility lines with large rocks and other objects that may be present in such conditions. If you come across such a situation, you should make several passes in the area surrounding the anomaly to look for any further evidence that it may be a utility line. If nothing comes up, you can probably rule it out as being just a large stone or something similar.



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