GPS Streamlines Earthmoving Projects

Kerr Construction uses the technology to eliminate rough grade stakes. A Caterpillar D6R dozer with an automated system is used to mark grade for other equipment on the site. "We cut grade holes everywhere so the scraper hands can see them," says Kerr. "They do not have to interpret stakes anymore. We cut the grade hole and mark that as grade or push up grade in the fill area. We will go in and make those on a grid."

This technique has saved Kerr Construction the expense of rough grade stakes. Consider the company's current project. "On this 100-acre site, it is probably a $50,000 to $100,000 savings," says Kerr.

Kerr uses the elimination of rough staking as a marketing tool. "When we get down to negotiating the project, we say, ‘We have GPS. You don't have to spend $50,000 to $100,000 on the rough grade'," he explains. "That is just another savings for the owner, but it helps us get $15 million projects. I don't even blink when I think about the $120,000 we spent on the Topcon system."

But rough grading is only one aspect where the GPS system benefits Kerr Construction. "We feel there is a production gain of 40% to 50% just on finish grading," says Kerr. It minimizes the re-work. "When you set the blade down, you know where grade is. It does not matter if it is in between 50-ft. staking or 20-ft. staking." This really helps in the grade transition areas where you would traditionally cut and fill, maybe overfill by a couple of tenths, then have to come back in to clean it up.

By creating topos and working with electronic files, Kerr Construction has also been able to resolve design problems earlier in the process. "If there is an issue in the design, it is better to find it early than late," says Kerr.

One such problem became apparent when a topo was performed for the 100-acre site Kerr Construction is currently on. "From a value-engineering standpoint, the first thing we do is a topo, just to check the topo with the engineer," says Kerr. When the topo was performed, it did not match the engineering data. "It was from half a foot to a foot high everywhere. We went to the owner and said, ‘We think there is a problem; we need your engineer to check with us.' They figured out they had made mistakes on the topo. We went back and adjusted all of the design elevations and solved the problem before we ever started. That saved us from having an 80,000-yd. stockpile a year later. You save that whole discussion with the client about the pile that costs $400,000 to haul away."

All of these benefits make it difficult to pinpoint exactly how long it takes to make a return on your investment. "It depends on how you are looking at things," says Kerr. Consider the potential $400,000 pile above. "In that case, it has paid for itself three times over already because we did not get stuck hauling that pile away. That was the first week we had it on the jobsite."

Manage the Site

GPS systems simplify your ability to manage your jobsite. "A topo of the site can be done rapidly with GPS and one person," says Fred Rogers, segment market manager, machine automation, Leica Geosystems. "That can be printed out and it will tell you the volume of dirt moved. You can get an estimate of what the cuts and fills are and where you are in your production."

The GPS performs this task much quicker and more accurately than the traditional method of creating a topo. "When you do a topo conventionally to calculate volumes, you do it in a grid," says Rogers. "That could be a 25-ft. grid. It could be a 50-ft. grid." Blue tops are driven into the ground to grade on a grid. You know you are correct at the blue top, but between the blue tops, you are not really sure.

The GPS can solve this problem by quickly checking the grade at more closely spaced intervals. "The surveyor can topo the site quicker and take shots at whatever intervals he programs it to - every 2 ft., every 10 seconds, every 2 seconds, etc.," says Rogers. "They will have a tighter topo map of the site." This data can be captured to create a model, which can be compared to a previous model to determine the volume moved.

The typical accuracy of the GPS systems is a tenth of a foot. But the ability to record data points in a tighter grid pattern increases accuracy over traditional topo methods. "Even if you have an error of 1.2 in., a 2-ft. grid pattern would be more accurate than a 50-ft. grid. Between the 50-ft. [data points], you don't know what is happening," says Rogers.