BY DON TALEND T he construction of a short stretch of a state highway in northeast Arkansas reveals the potential of using stakeless, stringless construction techniques to complete an entire highway cross-section, from subgrade to base to paved surface. Almost as importantly, the project utilizes automated grade control technologies on some machines that are relatively new to them. Starting in late summer 2012, Weaver-Bailey Contractors, El Paso, Ark., began constructing a four-lane, six-mile stretch of Highway 67 near Cash, Ark. e contractor trimmed an average of 4 inches of topsoil from the subgrade, constructed a 6-inch layer of Cement Stabilized Crushed Stone Base (CSCSB) and a 1-inch-thick asphalt bond-breaker installed to prevent overlay cracking, and planned to overlay the bond-breaker with a 10-inch layer of concrete pavement. e new stretch of Highway 67 is replacing “Old Highway 67” between Cash and the city of Hoxie to the north. Construction of Highway 67 near Cash, AR has been using laser/ GNSS automated grade control on four machines—including this Vögele Super 2100-2 paver—that are relatively new to the technology. Stakeless, Stringless— TOP TO BOTTOM Topcon Positioning Systems Displayed with permission • Machine Control Magazine • Vol. 3 No. 1 • Copyright 2013 Spatial Media • www.machinecontrolonline.com
Transcript
By Don Talend
T he construction of a short stretch of a state highway in northeast Arkansas reveals the
potential of using stakeless, stringless construction techniques to complete an entire highway cross-section, from subgrade to base to paved surface. Almost as importantly, the project utilizes automated grade control
technologies on some machines that are relatively new to them.
Starting in late summer 2012, Weaver-Bailey Contractors, El Paso, Ark., began constructing a four-lane, six-mile stretch of Highway 67 near Cash, Ark. The contractor trimmed an average of 4 inches of topsoil from the subgrade, constructed a 6-inch layer of
Cement Stabilized Crushed Stone Base (CSCSB) and a 1-inch-thick asphalt bond-breaker installed to prevent overlay cracking, and planned to overlay the bond-breaker with a 10-inch layer of concrete pavement.
The new stretch of Highway 67 is replacing “Old Highway 67” between Cash and the city of Hoxie to the north.
Construction of Highway 67 near Cash, AR has been using laser/GNSS automated grade control on four machines—including this Vögele Super 2100-2 paver—that are relatively new to the technology.
Stakeless, Stringless— Top To BoTTom
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Displayed with permission • Machine Control Magazine • Vol. 3 No. 1 • Copyright 2013 Spatial Media • www.machinecontrolonline.com
The turnkey project, which will see the highway open when all of the bridges and other work are completed, is expected to be finished in late 2013 or early 2014.
New machines used a new wayTrench Safety & Supply, Inc., North Little Rock, Ark., and representatives from Topcon Positioning Systems equipped a Gomaco 9500 dirt trimmer with a Millimeter GPS+ automated grade control system to fine-grade the subgrade.
In addition to a GNSS base and rover, the 3D system uses a PZL-1 Lazer Zone transmitter and a PZS-MC machine-control sensor or PZS-1 rover sensor that gets integrated with the contractor’s GNSS receiver. The PZL-1 transmitter sends out a wall of laser light 33 feet tall and up to 2,000 feet in diameter. The contractor can link up to four transmitters and the PZL-1 transmitter can operate multiple machines equipped to accept its signals. The GNSS component of the system plots the location of the machine while the laser component guides the grader to position and elevate the blade precisely. The system calculates the vertical angle from the laser up to the sensor on the machine and gives a vertical correction to the GNSS system, allowing quarter-inch accuracies.
The system trimmer on Highway 67 had dual sensors for elevation control on both sides of the machine. The sys-tem also provides automated steering for width control. The GNSS coordi-nates and laser beam were processed by the machine’s G21 controller, which guided the machine. In one pass, the trimmer dug out several inches of dirt from the subgrade using an auger and teeth-equipped trimmerhead located
on the underside of the machine, near the front. Trimmed dirt was placed onto the shoulder using the trimmer’s long conveyor located at the back of the machine.
The automated grade control system also was used on a Vögele Super 2100-2 paver, which was used to install the CSCSB layer at a width of 30 feet. Existing survey data from trimming work were available for use by the Vögele paver, which otherwise paves asphalt. These unique machines are designed to pave in great width for significant highway work productivity using a wide auger system on the front of the machine and a vibrating screed. Another boon to productivity is the machine’s high-compacting screed option, which Weaver-Bailey is using on this project. The screed has tamper bars that oscillate at high frequency, compacting the CSCSB almost
completely and to a much greater extent than other pavers. The high compaction limits the number of passes to one.
This was the first such machine to be equipped with a Topcon automated grade control system in the United States; automated grade control has been used on Vögele Super Series pavers in Europe several times. The automated grade control system used on the machine controlled steering as well as the elevation of the CSCSB surface; the tolerance was plus- or minus-1/4 inch.
The Vögele paver was equipped with the manufacturer’s Navitronic Plus, a built-in 3D open interface/open port system that is compatible with com-mercially available automated grade control systems. The automated grade control system on the machine includes two Navitronic Plus operating consoles for the screed, dual masts for mounting
The contractor, Weaver-Bailey Contractors of El Paso, AR, used a Gomaco 9500 dirt trimmer equipped with dual sensors for elevation control on both sides of the machine.
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Displayed with permission • Machine Control Magazine • Vol. 3 No. 1 • Copyright 2013 Spatial Media • www.machinecontrolonline.com
the 3D receivers, an angle sensor for the mast, and sensors for picking up displacement of the screed’s extending units. The sensors on the two extending units pick up the screed’s width; the machine is reportedly the only paver on the market with automatic screed extension control.
The Millimeter GPS+ system sent commands to the Navitronic Plus system to move the machine left, right, up or down. The operator views the model on an in-cab GX-60 controller. While the system hardware is inter-changeable for the different machines that Weaver-Bailey is operating on the job, the software was configured to fit each machine.
Much less costlyJamie McAnelly, project superintendent with Weaver-Bailey, noted in mid-November 2012 that the objective was to get the subgrade and CSCSB work completed as soon as possible so as to allow paving without major cold weather delays. By then, 50 percent of the trim-ming was complete; about 53,000 cubic yards of material would be removed eventually on the entire project area.
This was not the first time that Weaver-Bailey had used this automated grade control system on a trimmer, but it was the first time that the contractor had done such trimming work in entirely stakeless and stringless fashion. Weaver-Bailey had used the system on a trimmer on Highway 65 near Grady, Ark., but checked the grade with stringline a couple of years earlier.
McAnelly looked forward to using the system on the Vögele paver to control the CSCSB grade, having seen Weaver-Bailey’s first stringless trimming work. “We have actually
used a rod and level to verify some of our grades and we were within two- to three-hundredths, with many places having dead-on perfect grade,” he said.
Conversely, “When you use your GPS alignment, all you’re doing is an offset off of the polyline and it’s automatically there and you’re trimming in just a couple of minutes,” McAnelly said. “That was the biggest thing that increased our production. Now, it’s just changing a couple of numbers and we were back flying again.”
To McAnelly, time is money when it comes to minimizing paving time. “It’s not just materials,” he said. “The stringline, you don’t think that’s very expensive, but that’s a consumable that you no longer have to purchase. That and pins—there are a ton of pins. We’d be putting the pins in every 30 feet for six and a half miles—that’s a lot of pins and lot of expense right there in itself.”
McAnelly recalled previous paving projects in which pins for stringline deployed to serve as a guide for elevation had to be moved several times in one phase because the subgrade, CSCSB and paving passes had different widths. “Now, instead of taking that stringline crew and using that labor force for setting stringline, you take that crew and have somebody in it who’s knowledgeable about surveying to set control points,” McAnelly said. “When you get that right, you don’t have to reset those points. Those control points are the same ones you use to trim the subgrade, put down the CSCSB, and put the concrete down.” Essentially, stakeless, stringless pavement work allows Weaver-Bailey to work more profitably because the contractor spends more time laying down material and less time setting up and tearing down stringline, he added.
A typical stringline crew consists of four to eight workers, McAnelly noted. “On a job like this, I would have a stringline crew devoted to setting up and tearing down the string line for each evolution,” he added.
When it comes to employing stake-less, stringless automated grade control systems, system quality control takes on increased importance, McAnelly noted. “There’s a phrase we use a lot out here when using this equipment: garbage in, garbage out,” he said. “If your control points aren’t properly set, if your lasers aren’t properly set up, if the numbers on your machine aren’t properly set up, you’re going to get an improperly done product.” Checking these items can result in less downtime overall, he added.
Ensuring system reliability can impact the bottom line in a big way, McAnelly contended. He estimates that the use of stakeless, stringless technolo-gies reduces labor hours by at least 40 percent on a project like Highway 67. It’s a case of technology allowing professionals to focus their efforts on managing outcomes rather than manual labor routines.
More efficient pavingWeaver-Bailey also planned to use the dual-antenna automated grade control system on a two-track Gomaco PS-2600 Placer/Spreader and a Gomaco GHP-2800 four-track slipform paver while placing the concrete overlay, starting in late 2012 or early 2013. The system controls both pavement elevation and steering on the machines.
To maintain a high level of productiv-ity, Weaver-Bailey planned to use dump trucks to place fresh concrete from an onsite plant onto the CSCSB, ahead of
Displayed with permission • Machine Control Magazine • Vol. 3 No. 1 • Copyright 2013 Spatial Media • www.machinecontrolonline.com
the placer/spreader, which places the material to a “rough” elevation using its pan and an auger to spread it on either side of the machine to maintain a pavement width of 26 feet, allowing for 12-foot lanes, plus 2 feet of shoulder on the outside of the right lane. The concrete has a better workability by the time the paver processes the material a few seconds later using two machines.
Roger Weaver, paving superintendent with Weaver-Bailey, points out that setting stringline on either side of the machine for pavement in both directions would require about 25 miles of stringline. “That, right there, is a pretty considerable investment in time, manpower and material,” he said.
The slipform paver provided a finish edge to the pavement and used hydrau-lic vibrators on the front of the paver, rather than a vibrating screed like that used on the Vögele paver, to eliminate air pockets. The machine also placed dowel bars every 15 feet.
Weaver agreed with McAnelly that the stakeless, stringless technologies would likely save about 40 percent in labor on a project like this. “It would probably take six guys to set stringline and they could set maybe a mile a day if they really, really worked at it,” he said. Weaver added that placing the CSCSB with conventional grade control processes would require a dozer, motor grader and a roller and material overruns would probably occur at as much as 25–30 percent. Using the stringless method, he expected material overruns of 2 percent or less.
“If everything is working right, we have to pause at about 1,500 linear feet without any problems on a good day,” he said. “If we did it the old way, we’d do less than half of that and it wouldn’t be nearly as close to grade.” MC
Don Talend, Write Results Inc., West Dundee, IL, is a print and e-communications content developer specializing in covering technology and innovation.
The highly productive project is reportedly the first in the United States in which automated grade control has been used on a Vögele Super Series paver. That machine was used to install the Cement Stabilized Crushed Stone Base.
