Project Profile: Cutting Slopes Surgery in Progress

Jan. 1, 2011
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An Oregon excavating contractor has found that a 2D guidance system improves productivity of an excavator by 30 percent when cutting slopes to a precise grade.

About a year ago, Pihl Inc., a grading and excavation contractor based in Banks, OR, bought the Power Digger Pro guidance system from Leica Geosystems and fitted it onto a Kobelco 235 excavator. The system features a display screen in the cab that shows actual bucket position relative to the design grade.

“The guidance system has done a very nice job for us,” says Matt Pihl, owner of the company. “We use it to cut a lot of slopes. If you have a certain slope to cut, it has to be done precisely. You can make a big mistake if you make one gouge into the slope.

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“The Power Digger makes our excavator 30% faster when you’re on the final grade,” says Pihl. “But the best thing is that it eliminates a grade checker. That saves us significant money. And it’s safer, because you don’t have somebody walking around the moving equipment.”

Pihl recently used the guidance system to help cut a 1:1 slope involved in the site preparation for Progress Ridge, a retail shopping center in Beaverton, OR. It’s a big project: The site covers 14 acres. Pihl has exported 37,000 cubic yards of earth offsite and moved about 20,000 yards from cuts to fills on the site.

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The big 1:1 slope measures 30 vertical feet from top to bottom and is 400 feet long. At the toe of the slope a 20-foot-high retaining wall will be built for the length of two two-story buildings. That wall will then be backfilled and become part of the building.

About halfway up the slope a second wall, this one 5 feet high, will be built parallel to the first wall. The buildings will have a front entrance at the lower level, and a rear entrance one level up. There will be a third building next to the other two with stairways between the buildings.

To cut the 1:1 slope, Pihl used two excavators: a Komatsu PC 450 and the Kobelco 235 with the Power Digger guidance system. The Komatsu began the mass excavation by loading two off-road trucks and building a bench about halfway down the tall slope.

Next Pihl positioned the Kobelco on the bench and cut the 1:1 slope exactly to grade. “Then we cut out the first bench with the big excavator, and also used it to cut a second and final bench below the first,” says Tomas Zilka, Pihl’s surveying manager. “After that we could move the Kobelco down to the second bench and finish cutting out the slope.

“We didn’t use any stakes on the slope itself-only at the top, to tell us where to start digging,” says Zilka. “Laborwise, the Power Digger saved us a lot of labor, because otherwise we would have needed a grade checker.” He said it took just three days to cut the slope.

The Power Digger Pro works with four sensors mounted on the excavator, says Joe Marlette, machine-control specialist with Kuker Ranken Inc., the Portland, OR-area Leica dealer. One sensor is attached to the quick bucket release, and a second sensor is mounted on the excavator stick. That latter sensor is also a laser receiver. A third sensor is on the boom, and a fourth is mounted on the rear of the machine to sense pitch, roll, and rotation.

An operator can begin work in one of two ways, Marlette says. He can touch a reference point with the bucket, zero the system, then enter a design depth and slope into the onboard computer. With that, the system will display the bucket’s position relative to the design.

Or, the operator can set up a rotating laser, and pass the receiver on the excavator’s stick in front of the laser beam to use it as a reference. That’s how Pihl does it. “The operator measures the difference between the laser height and the future depth, and enters that measurement into the on-board computer,” Zilka says. “From there he can start digging.”

Zilka says he gets excellent service from Kuker Ranken. “I called them just the other day to ask a couple of technical questions,” he says. “Joe Marlette had the answers right away.”

Completion is slated for December. Zilka is pleased with the Power Digger Pro. “For our purposes it is absolutely perfect,” he says.