By Janis Keating

Earthmoving struggles to balance the massive and the minute. Huge amounts of soil and rock must be moved onto or from a site by large machines not known for their delicacy, and the results must conform to small tolerances or specifications. (An inch of error can become a foot's worth of trouble further down the line.) Some bulldozers and graders do meet those minute tolerances, with some help from above—12,000 mi. up in space, to be exact.

Machines equipped with the Trimble SiteVision control system receive signals from the global positioning system (GPS), which not only directs the equipment around a site but also controls blade elevation to within 20- or 30-mm accuracies. The benefits of SiteVision are immediately evident: Guiding machines with GPS eliminates the need for staking a site; earthmoving is done right the first time, with much less rework; and automating tasks means lower labor costs and higher profits.

Steep banks and elevated curves, two of the most difficult areas to grade, are made easy with SiteVision; there's no need for stakes, and the bank can be graded with fewer passes.

Using Skyways for the Highways
Highway expansion was needed for the traffic expected to be caused by the 2005 US Open Golf Championship to be held in Pinehurst, NC, near Raleigh; Sanford Contractors of Sanford, NC, submitted a bid to prepare part of the site (3 mi. of four-lane roadbed on both US Highway 1 and the US Highway 421 Bypass). After winning the bid, Sanford Project Manager Ian Scott installed SiteVision on several machines. Thus far, SiteVision is helping him "catch up" on a previously slow season.

"We had over 100 inches of rain in 2003, and most came in our usually busiest month; we lost over 125 days," Scott reports. "SiteVision makes our work go faster—perhaps 30% faster. We're still hauling the same amount of dirt—just getting it there faster."

Charlotte, NC's Spectra Integrated Systems Inc., a Trimble dealer, installed the SiteVision systems. "About the same time we got the highway jobs, we were looking at the Trimble systems. We tried them out, and we liked [them] so much we bought four new machines to use with SiteVision. It took about two days to install the SiteVision onto them," Scott explains. "Spectra did a nice, neat job putting it all together. We now have SiteVision on a [Caterpillar] 14H motor grader and three Caterpillar D6N bulldozers."

Before the earthmoving machines do their work, a site must have topography assigned to every inch—every x, y, and z coordinate—which usually is accomplished by surveying with Trimble's RTK, or real-time kinematic, Total Station GPS. Once the design firm and the engineers decide what to do to the site, their designs—if on blueprints—must be translated into electronic data; if the designers use AutoCAD or other popular software programs, those data can be imported directly into Trimble's Terramodel program. When all of the information—the site's current parameters and coordinates, as well as its finished parameters—is loaded into a computer, it then is downloaded into each individual earthmoving machine's SiteVision operator console through use of a PMCIA card.

"Spectra's Construction Data Service Division helped us make the 3D computer models for marking the site," Scott explains. "These models are loaded into our office computer, as well as into the modules in each."

SiteVision's in-cab display shows the operator's relative position to the road or site.

Operating Hands-On or Nearly Hands-Free
On a bulldozer or a motorgrader, SiteVision can operate in "indicate" or "automatic" mode. Indicate mode offers the operator a "targeting system" somewhat reminiscent of the controls for a Rebel X- or Y-wing fighter from Star Wars. Lightbars and a graphical color display use the project design information, 3D GPS position, and cross slope to show the operator what blade elevation and cross-slope movement he must use to get to grade. SiteVision's dual GPS antennas furnish data that pinpoint the exact position, slope, and orientation of the cutting edge, allowing the operator to grade complex designs faster.

On dozers and graders using the automatic blade control option (as Sanford Contractors' vehicles do), the GPS device is connected to the machine hydraulics, and the blade is moved automatically to the exact elevation and cross slope, providing significantly better accuracy. If large cuts are required, the operator can offset the design surface so smaller amounts are cut on each pass. SiteVision then knows exactly how much earth to move at which coordinates.

Did these high-tech gadgets unnerve Scott's crew? "Spectra Integrated came out and did extensive training the first day we had the machines. A few of our guys were apprehensive—scared of computers—but they caught on really fast. SiteVision's user-friendly; the learning curve was extremely quick. The crew likes SiteVision; now they don't want to be without it. Plus, if we have any problems, Trimble and Spectra have really good customer support. If we can't handle [a problem] over the phone, they can be here in two or three hours if we need them," Scott says.

To ensure precise positioning while the machines are moving, the SiteVision system uses RTK GPS, which requires two GPS receivers. One receiver, known as the GPS base station, is fixed in one precisely determined location. The second receiver is mounted on the user's bulldozer, motor grader, scraper, or excavator. Both receivers receive the GPS satellite signals at the same time. The reference station broadcasts its observed information, together with its location and other information, across a wireless radio link to the machine-based receiver. This receiver combines the base data with its own GPS data to compute a very precise position relative to the base station.

Two GPS antennas mounted onto each end of the machine's blade determines their exact position; this allows for very accurate cross-slope and heading data. This is especially advantageous for operations with dozers with angle blades (six-way blades), for operations with graders, and on complex design surfaces, such as super-elevation grading tasks.

"We're really pleased with SiteVision so far; it's been a really big help on this job," Scott adds. "You don't need to have two or three people out there checking grade by hand—we get it right the first time. Another company started working on another section of the highway at the same time we did; we're a little ahead of [that company], and we've started to fine-grade. SiteVision has made us a much more lean, productive operation."

Sanford Contractors is one of the few crews in the area to employ the SiteVision system. "It gives us a leg up on the competition," Scott says. "We're getting ready to work on a high school soon, so we'll see how it works on a building site. I can't say enough about how much work it saves—it makes us more productive, and we'll make more money on each winning bid because of SiteVision."

Janis Keating is a frequent contributor to Forester Communications publications.

GEC - January/February 2004