Extending the Reach
by Don Talend
September 1, 2009
The bridge on Higley Road, a major north-south arterial east of Phoenix, crosses a wash in the Eastern Maricopa Floodway. A lane was to be added in each direction, necessitating the construction of five piers to support each new traffic lane. Photo credit: Don Talend
A bridge-widening project near Phoenix uses machine control for deep, narrow excavations.
In early 2009, Haydon Building Corp. of Phoenix was awarded a $7.9-million contract by the town of Gilbert, Arizona, for bridge widening and roadway section improvements. The work was along Higley Road, a major north-south arterial in Gilbert, which is a southeast suburb of Phoenix. A lane was to be added in each direction over a wash in the Eastern Maricopa Floodway that passes under the existing 450-foot bridge.
Jeff Fields, Haydon’s GPS manager, saw an opportunity to use Global Navigation Satellite System (GNSS) technology for a cutting-edge task: verifying the location, dimensions and wall slope of 10 footing excavations. The 10 footings were designed to support five piers on either side of the existing bridge, which support the new lanes on the box-beam girder structure. Each footing excavation was to be 27 feet deep, 97 feet long and 70 feet wide.
“What we’re doing a little differently with the 3D system is the holes we’re digging,” Fields says, adding that most contractors that he knows of have used 3D machine control for applications such as grading roadway subgrades.
Outfitting Excavators with GNSS
Haydon Building Corp. used Topcon’s X63 excavator control system and a cellular network operated by Branco Machinery to dig pier footing excavations for a bridge-widening project near Phoenix. Jeff Fields of Haydon (left) and Todd Hermsen of Branco Machinery point out that the system eliminated the need for staking, for topographical verification using conventional surveying techniques and for a worker to enter the excavation. Photo credit: Don Talend
“Jeff’s been bringing a lot more to our attention, what we can do with the system, so I thought, heck, we knew exactly what our excavations needed to look like,” Haydon Project Manager Troy Gjerde says. “I thought that maybe this system that Jeff was telling us about could work for them and really, the system worked just beautifully.” He adds that the system provided positioning accuracy within one-tenth of a foot.
Gjerde notes that staking the footing excavations would have taken a staking crew about two hours apiece at an additional cost of several thousand dollars. Use of the system also saved several thousand dollars that otherwise would have been required to pay a surveyor to verify the location, slope and depth of each excavation. “If we wouldn’t have had this system, we would have had to have a grade checker out here the whole time, pulling stakes and checking the slope continually,” Gjerde says. “I would say it would have taken us a half a day to a day longer.” By eliminating the need for a worker to physically enter the excavation for verification, Haydon also avoided time-consuming shoring procedures and eliminated a less safe work situation.
This 3D site model was loaded into the X63 system control box, allowing the excavator operator to view the model on the monitor and avoid over-excavation while minimizing material waste. Model created by Dirt Pro LLC.
Fortunately, the operators’ learning curve was not steep, Gjerde says. “We had three different operators—two very experienced operators and a guy who’s our universal operator—and believe it or not, the guy who’s the least experienced on the excavator did the best job with the system,” he says. “I don’t even think it was a matter of hours for them to learn it. I think it took a couple of the guys a little time to get the functionality of the module—what button to push to get the views—but once they figured that out, it was really simple for them.”
Haydon purchased its two X63 systems in 2008, so the Higley Road bridge-widening project was one of the company’s first uses of the system. The company may purchase several more X63 systems in the future as the technology becomes an even bigger part of day-to-day operations, according to Fields.
Accessing the Network
Also integral to Haydon’s success on the job was TAZNet (Topcon Arizona Network), an RTK GNSS network that provides the contractor with positioning corrections using cellular technology. Haydon pays for a subscription to the network, which is hosted by Branco Machinery of Gilbert.
TAZNet went online in mid-2007 and reaches the Phoenix and Tucson metropolitan areas. Using its subscription to TAZNet eliminated the need for Haydon to set up a separate base station on each jobsite. Todd Hermsen, a Topcon sales representative who works with Haydon, explains, “With a base station, you’re setting on a known point on that job and on that known point, that base station transmits to the machine or rover corrections of where it is. When you move to a cellular communication with a network, the machine is actually dialing up to that network via cellular communication and receiving its corrections.”
He adds, “What it allows [Haydon] to do is take their base and rovers that they may already have and instead of tying up that base station on that job, give them the flexibility of taking that base station and converting it to a rover. So someone like Jeff [Fields] is able to take it out and use it for his survey work and not have to have that base station on the job at all times.” Once Branco installed cables and sensors on the machine and activated the modem, Haydon began to access the the network via a wireless telecommunications service provider.
Fields adds that the use of cellular technology further enhanced productivity on the bridge project. “For one, you don’t have two sets of equipment to haul around,” Fields says. “The other thing is, you don’t have [a base station] sitting out in the middle of the road; if your control point is close to traffic, you don’t have it sitting there where it can get bumped around by machines.”
He notes that he was initially concerned about accuracy when Haydon started using TAZNet. “I gave it probably two months of rechecking everything,” Fields says. “I’d actually double-check the system’s accuracy with a total station, but I don’t have to anymore—I’m satisfied that the accuracy is maintained with the network.”
Gjerde adds that Haydon’s confidence in the system was such that the company relied on it heavily for a project involving the location of several miles of underground utilities later in the spring.
As Haydon demonstrated on this bridge-widening project, the breadth of GNSS-enabled machine control applications continues to expand, yielding benefits in the areas of dirtmoving productivity, worker safety and project profitability. Haydon’s work along Higley Road demonstrated the expanding reach of this technology in two respects: grading control for excavators and bridge pier excavations that require deep, narrow cuts with precise slopes.
Don Talend
Don Talend of Write Results, West Dundee, Illinois, is a publicity and communications project manager specializing in construction, innovation and technology.
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