By Janet McConnaughey
NEW ORLEANS — Radar used in the stealth bomber and to find roadside bombs in Afghanistan and Iraq is moving into the sewers of Louisiana.
The aim is finding empty spaces where dirt has seeped into sewers and water pipes before they spread to create huge potholes or sinkholes that can collapse roadways and sidewalks above them.
It’s a national problem.
All around the country, water and sewer pipes laid 50 to 100 years ago are cracked and breaking.
The radar was developed for the Defense Department. Researchers at Louisiana Tech University — bankrolled by a Florida sewer inspection company — adapted it to look for potential sinkholes before they reach the surface.
The system will be tested this month in Slidell, where a sinkhole that popped up this fall alongside a major thoroughfare caused big headaches.
“It was big enough that I could stand up and walk around under the roadway with no problems,” Mayor Freddy Drennan said. “We have school buses, cars, delivery trucks using that road. The good Lord just looked out for us is the only reason it didn’t cave in and somebody get hurt.”
The problem is not unique to Louisiana. The condition of the nation’s sewer and drinking water systems both received a D-minus in a 2009 report card from the American Society of Civil Engineers.
When dirt becomes saturated, water seeps to the lowest possible spot. It takes less energy for muddy water to drip into a cracked pipe than to slide around it. More dirt erodes into the pipe until, at last, there’s nothing holding up a road or other surface above it. The dirt also can clog pipes, backing up sewage into homes and businesses.
Slidell will be one of the first real-world installations for ground-penetrating radar technology developed by the Defense Department and refined for civilian use by Louisiana Tech associated professor Erez Allouche and his colleagues.
Robots already look for cracks and breaks in underground pipes, but the Tech-developed system looks past the pipe and into the dirt, searching for empty spaces.
If it signals a big void — 2 feet across or deep — a city road crew will dig to look for it, said Joe Purtell of Cues Inc., a sewer and pipeline inspection company based in Orlando, Fla. Cues bankrolled the project with $3.2 million of its own money and $3 million from the National Institute of Standards and Technology.
The system can find voids as small as 8 inches deep, Allouche said.
“But at this point,” Purtell said, “we just want to start with the bigger sizes and prove those out first.”
Ruston also is talking about a test but hasn’t set a date, said Joe Aillet, the city’s water utilities director.
Results from Tech’s test beds, where pipe is sunk into dirt and voids intentionally created, look good, he said.
“We’ve just got to look at the practical part. Is it quick enough, is it convenient enough, is it dependable enough, is it fast enough, can we use it on a regular basis, is it something applicable on a daily basis or unwieldy or expensive where you can’t use it every day?”
Still, he said, “This is an exciting venture we think will really prove beneficial for Ruston utility systems.”
Slidell had signed up even before the big hole under Gause Boulevard was found a couple of months ago.
“It had been washing out for years and years before it ever reached the surface,” said Councilman Jay Newcomb, a Tech alumnus. “If his system can help us — any community — identify those kinds of problems before they rise into view, that’s a tremendous help.”
Louisiana Tech and Cues have been working on the radar project for years. Purtell said it was too early to talk about what the gizmos would cost. “What we’re thinking we’ll do is lease them to trained contractors and utilities who have trained their people how to read the output,” he said.
Allouche, lead author of a paper about Hurricane Katrina’s damage to water and sewer pipes in Slidell and other communities in St. Tammany Parish, proposed the Slidell test in September 2010 but said the robot wasn’t ready, Newcomb said.
Newcomb said the test would be this month.
“The older sections of town or whatever other sections were submerged for a long time will be the high-risk areas,” Allouche said, but the city water department will decide which pipes to check.
“They’re the ones who know the system best, so we will just follow the lead,” he said.
A Canadian company — SewerVue, of Burnaby, British Columbia — already makes a robot with ground-penetrating radar. However, its antenna has to touch the pipe and Tech’s does not, said Andy Dettmer, a Tech graduate who is a civil engineer for Carollo Engineers Inc. of Dallas and a member of the Tech advisory board.
“That’s a major improvement,” he said. Cleaning big sewers can be expensive and very time consuming, he said.
Bob Whiteley, an adjunct professor at Griffith University and senior principal in Coffey Geotechnics of New South Wales, Australia, said a system he helped develop could find voids 2 inches deep behind 3-1/2-inch-thick concrete.
“The system we developed was essentially for application in old brick sewers and tunnels and mostly used together with normal visual inspection,” according to an email attributed to Whiteley.
At least one other Canadian company has a robotic system that operates in cleaned pipes.
“There are German and Japanese systems mounted on robotic arms for large diameter tunnels but I don’t know whether there are current commercial suppliers,” Whiteley wrote.
Purtell said more work on the Tech/Cues robot will include programming to analyze data from a spinning, steerable antenna so the robot — now only able to scan above a pipe — also can look past its sides.
“It takes an order of magnitude more work to do that,” he said.
With even more sophistication, he said, the radar could “see what’s happening on the outside of the pipe surface — if soil conditions are eating away at the outside of the pipes and … the rate of decay of rebar that’s spirally run inside the concrete pipe.”