GPS Systems for the Earthmoving Contractor

Mention "GPS" today, and a fair number of people can tell you that GPS stands for Global Positioning System, and that it's a satellite-based locating system. Ask how GPS is used, though, and most will draw a blank after mentioning in-car navigation systems, or, perhaps, the locator in a hiker's backpack.

GPS technology, of course, has expansive application, from helping farm tractors apply just the right amount of fertilizer to each area of a field, to helping ships and airplanes stay on course. And, as you may know, GPS technology is today also finding its way onto more and more earthmoving sites.

Tony Nyen, president of Nyen Excavating, Chaska, Minn., says that his father, Bob, founder (in 1968) and vice president of the firm, began watching the development of GPS earthmoving in the late 1990s.

"I was skeptical," says Nyen, "but my father assured me that this was the future. We bought our first system in 2000, a second a year later, and are contemplating a third. My father says that if he had to go back to the 'old-fashioned' way of grading—by that he means stakes and lasers—he'd quit running machines. GPS has been a fantastic tool for us."

Basically, the use of GPS on earthmoving sites falls into two categories: "machine-control" and "grade-control."

Machine-control systems, as the term implies, are designed to assist such machines as motor graders, dozers, scrapers, compactors and hydraulic excavators more efficiently cut and fill to grade. Efficiency is enhanced, because operators running machines so equipped always know two essential bits of information—where the machine is located on the site, and the position of its work tool in relation to the final grade.

A primary benefit of GPS machine-control, of course, is that earthmoving equipment now can get along quite competently without grade stakes. You still need to survey control points, but according to GPS suppliers, you typically can eliminate some 90 percent of the stakes that would be required on the same site without GPS.

Lower survey costs result, especially on deep cuts and fills that might need staking several times. And, because machines no longer must wait for stake placement, they go to work sooner. Plus, with very few stakes to run over, the cost of stake replacement is virtually eliminated.

The operator of a GPS-equipped machine, instead of squinting at muddy stakes and guessing about grade, looks at a crisp, clean, full-color representation of the jobsite that gives exact grade information, anywhere on site. The operator can use this information to manually guide the machine to final grade, or, if the machine is equipped with an interface between the control system and the hydraulics, the blade is automatically positioned as the final grade approaches.

The potential results are that operator productivity goes up (especially for those less experienced), and rework of incorrect grades goes down. The machine also may get to grade with fewer passes, so it will use less fuel and incur less wear. And, because fewer people and fewer machines are generally required on a GPS site, safety gets a boost.

If you're not ready to turn your machines over to GPS control, however, you can introduce yourself to the world of satellite-controlled earthmoving with a "grade-management" system. These systems—such as Topcon's Pocket 3D, Trimble's SCS900 site-control system, and Leica Geosystems' SR530 Geodetic RTK receiver (recently superceded by the company's System 1200)—have a wide range of capabilities. The functions of these systems probably most used, however, are grade checking, topographical surveying, and point location.

Using such a system, for example, you can step into a cut just made by a motor grader and instantly determine the grade in reference to the site plan. Or, by positioning the system over a water-valve riser or manhole (which may be lowered and covered with dirt when grading begins), the system records the exact location, then unerringly guides you back when these utilities need finding. The same holds true for recording survey points, which can be easily and exactly reestablished if need be.

You can also place the system in an all-terrain vehicle or carry it by hand to quickly do a topographical survey of a new jobsite. You can compare your results with the developer's plans, then immediately discuss any discrepancies.

"Plans based on an aerial survey can have a bust [error] of plus or minus 6 to 12 inches," says Don Ahmer, Jr., vice president and general manager of Read Excavating Co., Gilberts, Ill. "A site with trees, for example, can easily be a foot off. We use GPS to immediately topo every job we get. An error of even a tenth of a foot across a 100- or 200-acre site can make a big difference in yardage and balancing the site. We have to keep getting better at knowing what's really out there."

GPS grade-management systems, as do GPS machine-control systems, work by essentially combining a "GPS segment" and a "control segment."

With machine-control, the GPS segment does the locating (such as telling a dozer where it is on site), and the control segment, which typically takes the form of an electronic, three-dimensional (3-D) plan of the job, provides grade information. The electronic plan, or "digital terrain model" (DTM), is created with special software, loaded on a data card, and placed into the system's computer. Grade-management systems also use GPS as the locating segment, and the control segment can be either a DTM, or an electronic map of points and topographical layers that the system itself creates.