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July 15, 2003 - Construction Zone Magazine
More than Meets the Eye
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More Than Meets The Eye
Ground Penetrating Radar Sees Beneath The Surface
by Joe Wheeler
Most of the time, what lies just inches below our feet is a complete mystery.
Cables, electrical conduit, pipes... all of these can turn a construction site into an emergency when accidentley severed. To avoid costly mistakes, a Las Vegas company offers the magical eye of ground penetrating radar. But just rolling one of the devices over the ground isn't enough. One must know how to interpret the data.
WorldGPR Services, Inc. has become Las Vegas's busiest radar service thanks to an innovative approach to the art and science of seeing beneath the surface, and the keen insight into data interpretation offered by company Vice-President Ed Lake.
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Lake pointed to a photo of a parking garage with colorful lines painted on the surface. "These are our lines," he said. "And this is what was actually there." A second showed the floor cut away, and those lines revealed to be the exact placement of pipes and cables beneath the concrete. "We're accurate to a quarter of an inch," Lake said.
Without radar or x-rays or some form of seeing beneath the surface, construction companies working with existing structures often have no alternative but to dig and hope for the best. That means jack hammering out existing concrete and risk snapping post-tension cables, electrical conduit and plumbing. In all cases, doing so means construction delays and cost overruns as repairs are made on an emergency basis.
It can also make the property owner pretty upset.
Post-tension cables can be under as much as 70,000 pounds of pressure. When such high tension cables are cut, and the pressure instantly released, the cable retracts. The force is enough to rip up concrete along its length. Using radar to see the cables beforehand, crews dig down to expose them, and are able to create a pair of ends prior to removing the piece.
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Lake and his crew were at the Monorail Station under construction at the MGM. Support pylons for the monorail had to be sunk through the main entrance and underground parking structure until solid ground was reached. That meant cutting through two levels of concrete, each of them crisscrossed with a variety of cables and electrical conduit.
Before they showed up, what waited below the surface had been a mystery.
"They have no clue what's under there. The plans are lost," Lake said. "It's usually the old guy who's been on the property the longest who understands where everything is. It's in his memory. But when they give him that gold watch, all that data is gone."
WorldGPR's general contractors sounds like a who's-who of construction: Granite Construction. Perini. SIS Las Vegas. Marnell-Corrao. Clark & Sullivan Constructors. They recently did work for The Luxor, which pulled cobblestones out of a walkway and needed to know where the underground electrical cabling ran. The cables included all the conduit for slot machines and the casino's computers.
"We're a can-do company," Lake said. "And that's what they like about us. They'll call and say, 'We need you to come out because we're hung up.'"
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Fred Brooks, vice-president of WorldGPR, added that working with the client's schedule is important. They go out and assess the work to be done, then arrange a time for the scans that doesn't disturb the other workers or customers.
"We'll come back at four in the morning, or one in the morning, whatever it takes to do the job," Brooks said. "We're there."
Lake said he has been trained by the best. "I've got about five years experience (with this system), and 30 years experience in the testing field," Lake said. He's worked with ultrasonics and x-rays, and says the system he uses now is superior. "It is the non-electrical properties - the dielectrics- of the material that we image," he said.
The company is planning a trip to El Paso, Texas, to study a cemetery and locate missing grave sites. They'll be able to image the disturbed soils, and even the bones themselves.
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"We just did the parking area at Bally's." Lake said. "They had no clue what was there, and we found more than they expected." Somewhat skeptical, Bally's engineers cut a small test hole to verify Lake's findings. Lake smiled as he recalled how everything they had drawn out appeared exactly where they said it would. "They were amazed that we found what we did."
Once the scans are complete, the images are converted into drawings. That information is then incorporated into the job.
"We give them drawings on CAD, and they can lay them over their drawings and know exactly where everything is," Brooks said. "We're doing that for the Flamingo right now."
"It gives them an engineering tool," Lake said. "And allows them to set up an engineering strategy that can save them a lot of money."
WorldGPR uses a high-tech answer to the problem of using a computer screen on job sites in direct sunlight. Under most conditions, it is extremely difficult to see the computer screen, and since interpretation of data is the cornerstone of their business, the company came up with an innovative solution.
A MicroOptics eyepiece attached to a pair of safety glasses displays the computer screen in perfect clarity. The effect is like having the computer monitor hover before the eye, and allows a single operator to perform both the physical requirements of the scan while monitoring the data input. In addition to the clarity, the operator can use the device on a remote basis. He can be up to 50 feet away from the computer. MicroOptics has allowed WorldGPR Services to use their equipment to demonstrate its effectiveness in the field.
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PRESS: ONLINE MEDIA
