Project Profile: Making the Grade—With Precision

March 1, 2009
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Gx Bug Web
Gx Bug Web
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Gx Bug Web

The biggest challenges in airport runway projects often don’t lie within the sheer amount of dirt that must be moved and graded, but rather in the tight tolerances mandated by the Federal Aviation Administration (FAA).

In Cedar Rapids, IA, as it worked on the taxiway portion of a multiyear runway project for the Eastern Iowa Airport, the general contractor, Cedar Valley Corp., recently discovered that the best tool available to help meet those tight tolerances was the precise positioning made possible through its grading subcontractor’s GPS machine controls.

The Eastern Iowa Airport project in its entirety includes rebuilding the main runway and a parallel taxiway, as well as replacing multiple intersections between the main and secondary runways. FAA tolerances require grades within the project to fall between 0 and plus or minus three-hundredths of a foot. These tolerances are critical for producing a smooth, uniform surface for aircraft and providing proper surface drainage of stormwater.

“We actually have subcontracted the grading for three runway projects this year,” says Paul Ruckman, Global Positioning System technician for DeLong Construction Inc., based in Washington, IA. DeLong Construction was subcontractor for the rough grading at the Eastern Iowa Airport project. When applied as a surveying tool, GPS can be used to accurately measure the geographic area, allowing the technician more easily to employ a three-dimensional model of the finished project with the desired grade. As a machine control, it then guides the bulldozer or grader’s blade to accurately produce the modeled grade.

According to Ruckman, DeLong Construction’s contribution to the Eastern Iowa Airport taxiway was to be a two-phase job. “Our first step was to remove the old taxiway, stockpiling and recycling the concrete material. We then were to do the rough grading, prepare the sub-grade, and place the recycled aggregate back down for the general contractor to use as base for the paving,” he says.

The taxiway project, running 3,400 linear feet, consisting of 71,000 cubic yards of unclassified excavation, 25,200 cubic yards of topsoil, and including 68,000 square yards of granular surfacing, encountered challenges as soon as the old concrete was removed. In June 2008, Eastern Iowa was inundated with flooding of historic proportions that also affected the Cedar Rapids airport. Not only were there days when DeLong Construction’s employees had to travel two hours out of their way to reach the site because of road closings, but the sticky mud onsite hindered stabilization efforts. “We had to add fly ash to the dirt to help it stiffen up,” Ruckman says. “And at one point the mud was so thick that we had to get a bulldozer to pull the tiller through the grade. It was crazy.”

But in the end, it was the GPS machine controls that saved the day not only for DeLong Construction but also for Cedar Valley Corp. First, DeLong Construction created the sub-grade to the FAA-mandated tolerances of within four-hundredths of a foot, and the engineering firm Foth/Engineering Alliance Inc., sent out its surveyor to check the sub-grade in a 25-foot grid. DeLong Construction then placed the recycled aggregate on the sub-grade as unbound sub-base, and graded the rock to be one-tenth above grade so that the trimmer could cut the grade to tighter FAA tolerances within three-hundredths of a foot.

“After that, the pavers realized they couldn’t trim some of the areas to the tolerances expected. They had trouble keeping the grade in spec,” Ruckman says. The pavement also must remain within the FAA tolerances of within three-hundredths of a foot. “So that’s when they asked us to come back out and grade behind them to fix the errors,” Ruckman says. “There are a lot of variables involved to get tolerances like this out of the GPS system. Most people say that it’s only good to one-tenth of a foot. I say it is as good as the people operating it, from the design side to the machine side.”

“Without the GPS, it couldn’t have been done,” says Deran DeLong, general manager of DeLong Construction. “The old way of grading, with string lines, we would have had to trim the dirt a second time on the sub-grade. We are able to avoid that using the GPS. And with this particular project, we wouldn’t have been able to touch up behind the pavers like we did without the GPS machine controls, either,” he adds.

For its GPS controls, DeLong Construction uses the HiPer Lite 3D-MC system by Topcon Positioning Systems. This system allows automatic, stakeless grading as it communicates with satellites to accurately measure distance and elevation, so that it can control the cut-and-fill requirements. “With the Topcon GPS, we start with a two-dimensional drawing,” Ruckman says. “Using AutoCAD, we import it and turn it into a 3D model. Then we go into the field and do our localization. This places the drawing in the right location in the field. We then export it to the automated machine, which builds the grade based on the 3D drawing.”

Founded in 1994 by Dana DeLong-Patterson and Deran DeLong. Delong Construction’s initial expertise was in simple earthmoving. Since that time, the company has grown to 70 employees and offers heavy highway earthmoving, underground utility installation, site development, mine reclamation, concrete crushing, and demolition throughout the state of Iowa.

DeLong explains that when DeLong Construction installed its first GPS machine control system, he noticed the company was one of the first in the area to provide that capability. “It’s coming around, though. I see more and more contractors are realizing the benefits,” he says, adding that the company’s GPS equipment dealer, Des Moines-based Star Equipment, has been a great asset to DeLong Construction as it has added GPS machine-control capability to its machines. “Dan Wiese is the laser and GPS machine-control specialist at Star Equipment, and he’s been extremely valuable to us in the last three years,” says DeLong. Star Equipment also has branch offices in the Iowa towns of Cedar Rapids, Ames, and Waterloo.

“It’s our third season of using GPS, and we’ve added it to two or more machines every year,” Ruckman explains. “We currently have the GPS on two motor graders, five bulldozers, and three bases and rovers. Both Topcon and Star Equipment have been an integral part of our success in adding the GPS to our capabilities. Our grading work used to take a lot of babysitting-a lot of trial and error. Now we do all of our modeling in-house, and we build a 3D GPS model for every job we do.

“With the airport projects we handled this year-in Cedar Rapids, and the other two were in Independence and Iowa City, IA-the GPS provided the same results every time, allowing us to quickly grade to FAA tolerances,” Ruckman adds.

“In a nutshell, we get the grade into spec on the first try,” says DeLong. “There’s not as much work with the field layout and surveying, like we used to do. And being able to do it right the first time saves us money and time. It helps us finish more quickly so we can go onto the next project.”