SHIFTING SOIL

Today’s Best Practices for Multi-Channel Ground Penetrating Radar

It didn’t take long after utilities were buried underground that humans had a need to discover where they put them – somewhat equivalent in today’s world of using your friend’s cell phone to call the one you misplaced.

The art and science of locating and mapping the underground environment began in earnest in the 1800s when Boston designers were hired to build the first subway system in the country. When they began plotting the subway system, they found a tangled mess of aging infrastructure and poorly marked utilities. As a result, the designers leaned on subsurface investigations to locate and map the buried utilities.

In more recent years, remote sensing technologies – specifically wide-array, multi-frequency Ground Penetrating Radar (GPR) systems – have been incorporated into Subsurface Utility Mapping (SUM) and underground damage prevention programs to aid in safer utility tracing, increase accuracy of records, and amplify knowledge of unknown buried features. By embracing widearray, multi-frequency GPR, and its increasing benefits and use cases, the industry will see more efficient and safer project outcomes.

At their core, utility surveyors are tasked with mapping a complete picture of the underground environment. Traditionally, utility surveyors have utilized handheld electromagnetic devices and pushcart GPR to detect the location of buried structures. However, in densely populated areas with busy utility corridors, mapping with traditional EMI and 2D pushcart GPR systems poses unique challenges. Since many cities and towns have underground infrastructure that dates back more than a century, it is common to find utility systems with no metallic material. The lack of such a substance in underground assets makes locating with traditional methods problematic. In addition, many new telecommunication systems have failed to install tracer wires which makes it extremely difficult for conventional locating practitioners. However, wide-array, multi-frequency GPR systems can overcome many of the complications and hurdles presented by traditional methods and models, making this new approach ideal for complex sites and projects.

Aside from the necessity factor due to aging infrastructure, wide-array, multi-frequency GPR systems allow for safer practices for utility crews and the general public. In 1976, Culver City, California experienced a gas line explosion caused by a front-end construction material loader striking a high-pressure petroleum line, which resulted in nine deaths and 14 injuries. This tragedy was a stark and brutal lesson to the industry that traditional methods to pinpoint utilities using pipeline locators and test holes is a dangerous approach. In fact, the NTSB report found that the failure to complete the professional utility locating work prior to digging was one of the main causes of gas line explosion. Today, we know that if the team in Culver City had the ability to use a wide-array GPR system, the exact location of the underground gas lines would have been identified and incorporated into the construction documents, thereby preventing such tragedy.

In recent years, DGT has incorporated the use of wide-array GPR systems into its project workflow. By utilizing mobile mapping systems, we’re able to gather large quantities of underground data beneath busy roadways and highways without exposing professionals to unnecessary traffic risks.

“The safety of the professional teams on the ground, and the communities in which we serve, is paramount to success,” said Michael Clifford, PLS, Principal at DGT Associates. “Surveyors, and all in the industry, should embrace the opportunities that advanced technology provides us in fulfilling our professional duty – locating utilities with precision in a safe and responsible manner. As we look to the future and establish best practices, it’s clear that wide-array GPR will become part of our everyday work.”

Michael A. Twohig is the Director of Subsurface Utility Mapping of DGT Associates. He can be reached at mtwohig@dgtassociates.com.Live help

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