Technology in Construction: From Earth to Space and Back in Less Than a Heartbeat

March 1, 2009

“We’re essentially digging a huge bathtub,” says Dennis Batye, area manager and GPS coordinator for Livermore, CA-based Top Grade Construction Inc. Batye is referring to a 320-acre waterfront community that Top Grade built in Bethel Island, CA, on the California Delta.

A two-plus-year project completed last May, the new Delta Coves subdivision boasts 494 new home lots. More than 400 of the lots have private docks providing resident boaters with quick access to nearby “fast water” on the delta. Before construction, delta water was held back from entering the site by a levee controlled by the US Army Corps of Engineers. So on the landward side of the levee, Top Grade dug a huge lagoon. In February 2008, when the levee was breached, water flowed into the newly excavated lagoon.

Around the lagoon, the contractor built more than a dozen “fingers” of land extending into the lagoon and providing space for new home sites. That meant excavating and compacting a total of 6 million cubic yards of sandy soil in an area where the water table was high-only about 8 feet below the surface.

Boat dock areas required cuts, and the fingers had to be filled. Regulations prohibited subsurface water from leaving the site, so a slurry wall was built to surround the entire lagoon. And Top Grade cut two main drainage ditches in the bottom of the excavation and set up an extensive dewatering system. It required 20 large pumps and 8,000 feet of plastic pipe to remove water from the bottom of the excavation. Large water cannons, like huge sprinklers, sprayed the water up onto the fingers to help consolidate the fills.

To excavate the lagoon and build the fingers, Top Grade used a fleet of predominately Caterpillar earthmovers, and most pieces were fitted with Trimble GPS equipment. The fleet included:

  • 10 Caterpillar 627 scrapers fitted with Trimble GPS units;
  • five Challenger tractors pulling double Miskin cans (scrapers);
  • two excavators, a Cat 345 and a Cat 350;
  • four Cat dozers, including three D6 units and a D9, all equipped with Trimble GPS;
  • five vibratory rollers;
  • six articulated dump trucks (four Cats and two Volvo units);
  • one Cat 14H motor grader with a Trimble Blade Pro 3D GPS unit;
  • one Cat 623 scraper with a Trimble GPS unit.

Because the Corps of Engineers gave Top Grade a hard-and-fast March deadline by which the levee must be breached, Batye said the contractor was under heavy pressure to complete the excavation on time. “If they could not breach it by that date and turn it over to the [subdivision] owner, our company could have potentially faced a huge financial liability,” said Batye.

“The GPS equipment contributed mightily to our ability to meet the deadline,” Batye said. The GPSs provide each operator with a display screen showing the location of the machine’s blade relative to the designed cut or fill. “GPS probably saved us 20% of the time it would have taken without them. And we did it with less equipment. Without GPS, it would have taken three blades; we kept up with one blade. And it probably would have taken two more dozers and another Cat 623 scraper. We only needed three grade checkers with GPS rovers; without GPS we could easily have had seven or eight grade checkers.”

Top Grade is one of the largest users of Trimble GPS equipment on the West Coast. “We hang our hat on being market leaders in the use of GPS technology,” says Lee Myhre, marketing director at Top Grade. “GPS gives us a tremendous competitive advantage and allows us to pass savings back to our clients.”

Batye said Delta Coves was a complex project fraught with many challenges to overcome. Many of those challenges were solved by the project’s foreman, Dale Batye, who is Dennis’s brother.

Automatic Trimmer Replaces Two Blades
On a Texas tollway project, the road-building process is being cut short with a world’s first: a GPS-equipped road base trimmer that automatically steers itself, cuts grade to within a quarter-inch and takes the place of two motor graders, says the contractor.

The project is a $26.5 million earthwork-and-drainage contract to build a 6.5-mile stretch of State Highway 45 south of Austin. The contractor, T.J. Lambrecht Construction, is cutting the road’s subgrade and base with a Gomaco 9500 trimmer equipped with a Topcon Millimeter GPS unit. Construction began early last July and is scheduled for completion by May 1, 2009.

Cutting a pass 16 feet, 8 inches wide, the big trimmer is used at three stages of subgrade and base construction, explains Mike Wehling, Lambrecht’s regional survey and GPS machine-control manager. The contractor first employs an all-Caterpillar fleet of dozers and scrapers to bring the grade to within two-tenths of a foot. Two of the dozers are equipped with GPS units.

Next, the trimmer swings into action. It cuts grade with a rotating drum fitted with teeth. With the aid of the Topcon Millimeter GPS, the trimmer brings the grade to within one quarter-inch. Then a Caterpillar RM 500 stabilizer mixes lime into the subgrade 6 inches deep. The grade is rolled with a pneumatic compactor and cured for four days, says Wehling. Another phase of remixing and compaction follows curing.

“Then we run the trimmer on it again, for a second time, and get it to within a quarter-inch,” says Wehling. “Next we bring in 30 inches of select fill material, rough-grade that with the GPS dozers, and compact it again. The trimmer makes a final pass, once again bringing the grade to within one quarter-inch. That is followed by a tack coat, a 4-inch hot-mix asphalt base, and 12 inches of concrete pavement.”

The trimmer can produce the same amount of finished grade as two GPS motor graders working together, says Wehling. “The trimmer makes one pass and the grade is perfect, but with motor graders you have to make multiple passes. The trimmer needs to cut about two-tenths of a foot to keep the proper head of material in front of it. At that depth it can do up to 40 feet per minute under ideal conditions. If it has to cut more than four-tenths or five-tenths of a foot, we have to slow it down too much.

“We had the first two trimmers in the world equipped with Topcon Millimeter GPS,” says Wehling. “The GPS is used to control steering, and the Millimeter laser is used to control grade. At about 600-foot intervals down the road, we set up the fan-beam laser on control points. The trimmer uses two of them, and we leapfrog them one after the other down the road. The laser transmits a fan-shaped beam to the two receivers on the trimmer, one on each side.”

GPS Helps at Medical Center Excavation
“Knowledge is power,” says Gene Lowder, referring to the GPS that his company is using to help excavate 500,000 cubic yards at the Kernersville Medical Center in Kernersville, NC. “My operators say you’re always moving forward with the GPS units; there’s no guessing at where you are.”

Contractor Charles D. Lowder Inc. has equipped six earthmoving machines with Trimble GPS units to handle site preparation for the big medical center. Two major buildings will be located on the 70-acre site: the main hospital building, with a footprint of 244,000 square feet, and a medical office building with a footprint of 30,000 square feet.

Lowder is excavating with four Caterpillar 621 scrapers and two Moxy off-road trucks. The Trimble-equipped earthmovers are a Cat D5M dozer, a Cat D5N dozer with automated blade control, a John Deere 750J with automatic blade control, two Hitachi excavators, and a Caterpillar 12H motor grader.

Lowder’s Trimble system is a GCS 900 with MS990 antennas. With GPS monitors in the cabs of the six machines, operators can compare their blade locations to the required cut or fill at any given time. Lowder bought two Trimble SPS 851 base stations and an 881 Rover for grade checking. “We can share the rover among several jobs and maintain GPS-controlled equipment on all of them if needed,” says Lowder.

Cuts and fills are being balanced onsite at the medical center. Cuts range upwards of 20 feet and fills are 30 feet or more. As the scrapers haul to the fill areas, two GPS tractors work the area and monitor the toe of the fill and vertical placement of the soil, Lowder says. Meanwhile the third GPS dozer works next to a pipe crew to monitor the fill around the utility operation. At times, two GPS excavators dig out the basement of the hospital and monitor the level of that excavation.

Long-Boom GPS Excavators Work Underwater
In 2004, two hurricanes caused extensive damage to the intake and discharge channels for a nuclear power plant located on Florida’s Atlantic Coast. Wave action caused severe erosion of the channels’ embankments, and they needed repair.

“We had to remove the existing material and import a mixture of 70% Class 57 stone and 30% coarse sand to replace the material that had been eroded from the embankment,” says Larry Tarr, general manager for Blue Goose Construction in Fort Pierce, FL. That meant working underwater to repair the channel.

Long-boom excavators were the answer, but how could the operators read a grade when working underwater in the channel? With Topcon GPS, says Tarr. The contractor outfitted three sizes of John Deere excavators with long booms and GPS units. (The machines are available to other contractors on a rental basis.) A Deere 850D carries a 95-foot boom; a 450D excavator has a 75-foot boom, and several 240D excavators have a reach of 60 feet.

Working from the top of the levee beside the channel, the 850D did the mass excavation on the top portion of the levee, Tarr said. The 850D relayed material to a 240D working on the bottom of the slope from a barge. Next, the 450D handled the finish-grading of the slope.

The repair consists first of the 70/30 mixture of Class 57 stone and coarse sand, then a filter fabric, then a 6-inch-thick drainage layer, then another filter fabric. Typically, the 70/30 mixture is placed in 12-inch lifts and compacted by kneeing it in with the excavator bucket. Divers periodically go down in the channel and verify lift thicknesses. In some areas, fills of up to 10 feet are required.

“We had to have a system that could grade underwater reliably with great precision,” says Tarr. “That’s why we chose Topcon and Lengemann Co., the Topcon dealer for Florida. They were able to provide us with a system that could grade underwater and provide real-time location information about the bucket. The display provides the operator with a side view of the bucket, and its relation to the proposed grade lines. The operator can also see the tilt angle of the bucket so he knows when he is dumping or picking up material or using the specially designed grading buckets to grade the slopes smooth. We either remove material down to the design grade or fill material up to the design grade. Once we get to design elevation, we begin the finish grading operation.

“We are grading the 135-foot-long, 3:1 slopes, most of which are underwater, to a grade tolerance of less than five-tenths-and leaving a smooth, even finish,” Tarr says. “It’s challenging, but we could not have achieved this precision without the Topcon system.” The prime contractor, Underwater Engineering Services Inc., then installs a layer of articulated concrete block mats over the embankments, making for a clean, even finish that protects the embankments from future hurricane erosion.

GPS Saves Time on Dairy Farm Project
An earthmoving fleet owned by Mueller Excavating averaged 12,000 cubic yards of excavation per day while doing the site preparation for a large dairy farm in Rosendale, WI. Mueller, of Campbellsport, WI, completed mass grading for the 100-acre earthmoving project last August. With 8,000 head of cattle, this is the largest dairy farm in the state.

For the project, Mueller used three GPS-equipped machines: a John Deere 750J dozer with a Trimble 990 GPS, a Caterpillar D5M dozer, and a Cat 140M motor grader. Both of the Caterpillar units had Trimble 980 GPS equipment.

Mueller did the entire job with no stakes. Instead, GPS displays in the cabs of the dozers and grader showed the operators cuts and fills. The project included grading and excavating the foundations for two 1,340-foot-by-400-foot barns and milking parlors; digging three manure pits with a total capacity of 74 million gallons; digging feed bunkers that measure 300 by 400 feet and 800 by 600 feet; digging a 100,000-cubic-yard stormwater pond, and laying 3 miles of pipe.

“With GPS, when you work 10 hours a day, you get 10 hours of production, not eight hours of production and two hours of staking,” says Dustin Mueller, project manager for the contractor. “GPS saves us about 25%, timewise. We’ve been using GPS for about a year and a half, and it’s always been right on. In fact, other contractors working on jobs with us have had us use our GPS to check their manual staking.”

In addition to the two GPS dozers and the motor grader, Mueller used three Caterpillar 627 scrapers; five off-road haul trucks of both the Volvo and John Deere variety; four excavators, two of them from Volvo and two from Caterpillar; two Caterpillar sheepsfoot rollers; and two Volvo wheel-loaders.

“We used GPS right from the start,” says Mueller. “The GPS machines would tell the scrapers and trucks where the cuts and fills were, and then we’d grade it up with the dozers. Once we got the grade close we would flip on the automatic switch and grade it to plus or minus eight-hundredths of a foot.”

Owner Nick Mueller explains his company’s success. “Part of the reason we’ve been successful is that we know our craft and will do whatever it takes to make customers happy,” he says. “You have to stay current to stay competitive. The factory-installed Trimble system just makes it easier for us to do that on the Deere 750J.”
About the Author

Daniel C. Brown

Daniel C. Brown writes on safety and the construction industry.

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