They increase fine grading accuracy and drive up production.
The evidence is conclusive. Global positioning systems (GPSs) and automated grading controls offer a way to take your earthmoving productivity to the next level. Some contractors say, and seriously so, that these systems cut their production times in half, compared to grading by stakes. And such systems are the precursor to stringless paving, which is coming in the near future.
“Last month [in August] we had probably six good-sized jobs that should have taken us into the middle of October on a normal production schedule,” says Nick Mianecki, a civil engineering technician with Wanasek Corp., an earthmoving contractor from Burlington, WI. But the firm recently purchased two Trimble GCS900 grade control systems. As a result, production has speeded up greatly. “We did all those projects in August and early September,” he says. “They were new home subdivisions that averaged from 16 acres and up.”
Another example comes from Aaron Avery, who faced one large grading project just after New Year’s Day, 2006—the 102-acre parking lot for the new Arizona Cardinals football stadium in Glendale, AZ, near Phoenix. As project engineer for Mark Markham Contracting Inc. in Phoenix, Avery and his team took on nearly 700,000 cubic yards of earthmoving, placement of 151,000 tons of stone base and 71,000 tons of asphalt pavement.
The schedule was tight. “At the peak we had four Cat 627 scrapers and six Cat 623 scrapers,” says Avery. “We used four motor graders, four water pulls [tanks], and a Caterpillar 815 compactor.”
For the rough grading phase of the project, Markham used a Trimble GPS. An engineering firm created a three-dimensional model of the site, with both existing and final grades, and the contractor uploaded it into computers on-board one scraper and one motor grader.
When crews completed rough grading, stone base came next. “We would haul the aggregate base into the site at night,” recalls Avery. “Our operators are good enough to place 6 inches of stone base close to grade without any measurements.”
The next day, Markham’s Caterpillar 140H motor grader—fitted with a Topcon Millimeter GPS—would swing into action to do the fine grading. Topcon’s mmGPS+ system combines the benefits of global positioning satellites with the precision of laser-guided grading. With mmGPS+, a laser transmitter sends out a wall-like signal that heightens the accuracy of the GPS. While GPS satellites provide a high degree of accuracy, the laser provides the on-board blade control system with another point of reference.
“We got between one- and two-hundredths of accuracy at all times,” says Avery. He says the laser receiver is mounted on the mast fixed to the grader’s blade—just below the GPS receiver. “Your accuracy comes from the laser,” says Avery. “And the slower the operator goes, the more precise your grade is going to be. The Millimeter system has a display in the cab to show you the cut or fill at your given location.”
Avery credits the Topcon Millimeter system with helping complete the project within six months—by the end of June. “We could finish grade and get ready to pave on 25,000 to 30,000 square yards a day,” he says. “We used the Topcon system to help us get caught up. We rented the system, and it paid for itself in one job.”
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Photo: Trimble |
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A Major Advance
Topcon calls the Millimeter system, introduced in January 2005, a major advance in the industry. “GPS originally was for rough grading,” says Murray Lodge, the company’s director of sales for construction products. “GPS would get you fairly close. But now it has progressed, and we can do a lot of finish grading.”
Lodge says Topcon GPSs now can track, or will be able to track, all 24 satellites put up by the United States, plus the European constellation of satellites (called Galileo), and the GLONASS constellation of Russian satellites. More satellites mean more grading accuracy, Lodge explains. Because GPSs triangulate among points of reference to establish locations on Earth, using more satellites boosts precision. You need a minimum of five satellites to do surveying work, and with fewer satellites you can’t pick up signals from five satellites, Lodge says.
“Galileo will have 30 satellites, and Topcon will be able to use them all,” Lodge says. “GLONASS has about 15 satellites now, and by the end of 2007, they will have 24 satellites.”
What’s more, Topcon’s Millimeter system enables a contractor to control multiple grading machines from one laser transmitter. By contrast, with a total station system of controllers, you needed one total station per grading machine. “Now I can run as many machines as I want to, all from one transmitter,” says Lodge.
Automated Trimmer Control
At Lambert–St. Louis International Airport, a joint venture of Millstone Bangert Inc. and Fred Weber Inc. recently built a new 9,000-foot-long runway, two parallel taxiways, four high-speed taxiways, and 15 connector taxiways. Base construction called for 10 inches of 1-inch-minus aggregate (P-209, by FAA definition), topped by a 6-inch layer of drainable, cement-treated aggregate (P-308). Millstone Bangert used a Caterpillar D6 LGP with a Trimble GPS to grade the P-209 to the nearest 0.1 foot, says Bob Leingang, the contractor’s chief engineer.
“That’s when we started with the Gomaco 9500 trimmer with Leica total stations,” says Leingang. “The tolerances in the vertical element of the GPS aren’t tight enough for us. The owner’s quality assurance personnel were checking the subgrade for the 0.05-foot tolerances and we were obtaining grades within 0.005 foot.”
To control the trimmer for the P-209 base stone, the contractor used two Leica Total Robotic Stations, which are control units on tripods by the side of the area being graded. The first total station controlled the Gomaco 9500 trimmer, and the one behind it took as-built shots of the graded base. “Then we would leapfrog the stations as we moved down the grade,” says Leingang. “The one shooting as-builts would jump ahead and control the trimmer, and the second one would shoot as-builts.”
To place the drainable cement-treated base, the contractor used a Gomaco 2600 as a belt placer—or dumped trucks into a Gomaco 9500 and used it as a placer in front of the 2600. The Gomaco 2600 was controlled by two total stations to maintain alignment and grade during placement. “We were able to control the drainable base stone to within 0.005 foot as well,” says Leingang. “We used three or four stations to place the drainable base.”
Did the automated trimmer save time? “Yes, definitely,” says Leingang. “It increased our production in the neighborhood of 25% to 30%.”
No stringlines, as are conventionally required, were used in grade preparation at the airport. With the Gomaco-Leica system, a series of shots from the total stations to various reference points bring the total stations into the three-dimensional picture of the job site.
A Leica 3-D Command Center is mounted to the trimmer or placer and is connected to the CAN (controller area network) bus of Gomaco’s Network Controller. The 3-D picture of the project is downloaded into the Command Center.
At this point, all that’s left is to bring the trimmer, or placer, into the picture. To do that, shots are taken from the total stations at prisms mounted on the machine. By radio link, the total stations send signals or coordinates back and forth to the Command Center mounted on the machine.
Information is constantly updated throughout the process. As the machine moves, the total stations track it and send radio signals back and forth to the Command Center at a rate of up to eight times per second. In milliseconds, the Command Center takes the real-time coordinate data and compares it to the design-plan coordinate data. With that information, the Network Controller can guide and steer the trimmer.
Higher Production, Same Fleet
Wanasek Corp., the Wisconsin earthmover, recently finished fine grading a 300,000-square-foot pad for a distribution center. The contractor used a Caterpillar D6N, coupled with a GPS-driven Trimble GCS900 control system, to do the rough grading. Mianecki says he received the site’s CAD drawing from the developer of the project. Prior to ground breaking, he used Trimble’s Terramodel software to convert the CAD drawing into a 3-D digital site model.
“I can download the 3-D model onto a disk, and that goes into a computer on the dozer,” says Mianecki. Then the dozer goes to work. Each of two dozers has fully automated blade control.
How long did the big box site take? “With stripping and everything, we were in and out of there in three weeks,” says Mianecki. “And we were plus-or-minus 0.5 inch when we left there.
“To do that job with conventional surveying crews you would take maybe twice as long in the finish grading stages,” Mianecki says. “It takes extra time to work around stakes. But with GPS you don’t have to be careful around stakes. There’s no question that you’re right on the money. It goes a lot smoother.”
Mianecki says the company’s two GPSs have gained a leg up on the competition. “We’ve gotten a lot more responses now from general contractors who might not have asked us to bid,” he says. “Now, when we can deliver a pad right away, we’re seeing a huge response. I know we’ve increased our workload by 25%, and we haven’t increased our fleet size.”
An Internet Connection
In Georgia, Southern States Site Work and Underground Contracting LLC uses Trimble GCS900 Grade Control Systems on all of its dozers, excavators, and motor graders, and on its articulated trucks, says Gary McClure, machine control specialist. Three elements of information are loaded onto a 1-inch-square sandisk—the site survey file, the finished grade model, and machine dimensions that coordinate the blade to the receiver target.
“Once that’s done, you plug the card into the computer on the machine and it will show you a little picture of a dozer,” says McClure. “And you can see a cut or fill on the left side of the blade, and a cut or fill on the right side of the blade. Once you get within 3 inches, you can flip a button and it will go automatic. That will get you within 0.1 inch.
“You’ve got the whole job in one machine,” says McClure. “There’s no downtime waiting for surveyors. We feel like the return is greater than the cost, and the cost varies from $80,000 to $100,000 per grading machine.”
What’s even better, McClure says he can communicate from an office PC to the operator’s on-board computer through an Internet connection. The Trimble base station has a modem in it, and each machine has an Internet Protocol address. “I can send text messages to the operator, and if I have an updated site profile I can send that to the operator,” says McClure. “Plus, the Internet connection gives me the ability to run diagnostics on the machine’s grade control system. I can tell the operator how to fix a problem without visiting the site.”
Southern States is using the Trimble systems for grading control at two college dormitory sites, one in Tuscaloosa, AL, and the other in Hattiesburg, MS. At Tuscaloosa, the deepest cut was about 20 feet, and the biggest fill was 17 to 18 feet.
“Your project gets done about 40% faster,” says McClure. “You move dirt one time, and there’s no rework. Your operator error is less. We figure the payoff is about $6,000 per acre in survey costs.”
Hydrostatic Drive and GPS
At Cox & Sons Contracting, an Illinois contractor, president DeWayne Cox last spring bought an MG622 motor grader with hydrostatic drive from Pavement Services Inc. (PSI).
Like Arizona’s Markham, Cox runs Topcon’s Millimeter GPS laser-assisted system on his earthmoving equipment.
He bought the PSI motor grader because it has hydrostatic drive, which works best with a GPS, Cox says. Hydrostatic drive allows one to change ground speed on the motor grader yet not change the engine speed. That’s important, because the hydraulics that automatically and instantly change the blade position depend on a constant engine speed. If the engine slows down, the blade reaction time slows down, and your grade will not be on target.
“We use John Deere dozers with our GPSs because the dozers have hydrostatic drive,” says Cox. “You can make the machine move as fast or as slow as you want to, without changing engine speed.”
Cox says his company has performed 10 or 12 projects in 2006 with the PSI grader and Topcon Millimeter GPS. He figures he paid about $70,000 for the new automated grade control system, but says it paid for itself in three or four months.
The laser transmitter on the Topcon system can reach out for a long distance, Cox says. “We have grading projects that cover 150 acres and we can set up the laser in the middle of the site and reach all of the machines,” he says.
He runs a Topcon base station from the top of the Cox office building. “You can send a signal out for 20 miles,” says Cox. “So we can run multiple jobs all at once, from one base station. Those stations cost $25,000 each, so if you need six of them, that’s $150,000.
“This Millimeter GPS is the first step to stringless paving,” says Cox, who also does both concrete and asphalt paving. “We bought it so that we would be in on the ground floor.”
Many others are doing the same thing. Topcon says it is selling more than 1,000 units into the construction industry each year. Topcon’s market share has increased, and in some years its construction business has grown by 300%, Lodge says.
That’s for a good reason: improved productivity. The time is coming—and it’s not far away—when a contractor must have automated grade control systems to stay competitive in the marketplace.