Technology assesses bridge safety after powerful storms

“The strength of the bridge is dependent on how strong the soil is,” said Dr. Mohammed Gabr, a Distinguished Professor of Civil Engineering and Construction at North Carolina State University who developed the Soil Probe.

In the past, it took a long time to determine the stability of bridge pillars. Engineers took core samples with heavy and expensive equipment and required several hours or days for the results to be ready. For sand samples, scientists would pour expensive liquid hydrogen to freeze the ground so the sand’s original structure was preserved.

These limitations helped inform the requirements for the Soil Probe device, including minimal dependence on power and easy operation by two people. Also, with this probe, there is no need to gather samples for laboratory testing to assess the soil resistance to erosion.

“This device can be used in places where taking samples is not feasible,” Gabr said. “The testing is rapid—it can go 30 feet deep within five minutes—and can be done in many places along a bridge for a complete mapping of the bridge foundation support area. The most time-consuming part is driving to the site.”

 “How fast the soil washes away depends on how strong the soil is,” Gabr explained. “The probe would bury itself quicker in soft soil compared to strong, compact soil.”

Gabr and his team developed a prototype they tested in the lab and in the field. The last test was in 2016 after hurricane Irene opened a new inlet on Pea Island in the Outer Banks, North Carolina.

“The Department of Transportation was putting a temporary bridge over the new inlet,” he said. “After we tested, we confirmed the soil was safe for a permanent bridge.”

Standardization
Following the development and testing of the Soil Probe, Gabr wrote the standard with instructions on how to make and use the Soil Probe for the American Society for Testing and Materials International (ASTM) ASTM International, one of the largest standards development organizations in the country.

“It is a really big deal to get a new standard published,” said Hajian.

For this standard, ASTM required testing to get reliable, repeatable results.

“For a standard to come out, it needs to have 100 percent approval,” said Philip Mattson, Director of Office of Standards for S&T and Chairman for ASTM International Committee on Homeland Security.

“This is an example of a transition of a knowledge product, the Soil Probe, into a standard,” said Mattson. “A standard gives greater visibility and credibility because it goes through a much broader vetting process.”