Paving with 3D Stringless
Two of the first people at work on the paving side of the project were Kelly Steeves, Concrete Paving Manager, and Tracy Trane, Paving Engineer. As they began laying out paving passes for the project, it was quickly realized that paving with traditional stringline would not be feasible with the project’s tight working quarters and aggressive completion deadline.
“I was in charge of putting together the paving plan and actually had stringline laid out for the entire project,” Trane said. “Stringline just wasn’t going to work on the project for a variety of reasons, time constraints being one of the biggest reasons.”
The concrete is slipformed on top of a three inch (76 mm) thick asphalt base. Holes for the stringline stakes would have to be predrilled into the asphalt base, the stakes pounded in, and then the stringline set and fine-tuned. It’s a time-consuming process on a project where time is a precious commodity.
“The MOT and schedule drive the project,” Steeves explained. “Using the 3D Leica system, we are able to move our paving spreads in on the heels of the asphalt pavers and start paving concrete with minimal set-up time.
“The Leica system makes the paving operation much safer to work around than stringline. We do not have to contend with people tripping over or driving through the stringline. With the dynamics of the project, the large amount of foot and vehicle traffic, the Leica 3D system is one of the reason’s we are ahead of schedule.”
Most of PRC’s new crew had never paved with a 3D system. Learning stringless while establishing a system of trust between the paving superintendents on the seven different paving spreads and the 3D system was, at times, challenging.
Mike Sink, Paving Superintendent on the GOMACO GP-4000 paving spread, was new to 3D, but quickly came to realize the value of the system.
“It’s definitely a benefit,” Sink said. “It decreases the margin of error and increases productivity. It makes it easier to jump from pave to pave without having to stop to double-check stringline. It just has a lot more flexibility than stringline. Even setting up the paver, we use the total stations to make sure our pans are set up straight and square with each other. Shoot the pan, shoot the stainless, and you can calibrate the paver a lot more effectively than you ever could using stringline and a level.”
Gaylen Gough, Paving Superintendent for the GOMACO Commander III with V2 mold, was doubtful of 3D, too, but quickly saw the advantages to the system.
“I was skeptical of the stringless, but I became convinced of its abilities. When you’re on stringline, you’re committed to either a full turn or a half turn with the grade jack, if you can get the handle to stay standing up. With 3D, you can take that one full turn and split it into 10 different elevations allowing you that much more success in getting a good ride out of your concrete.
“Right out of the gate, we were hitting good numbers and getting good rides with this stringless system. It also eliminates all of the headaches about truck access, tripping over the line, finishers having to worry about the line with their handles, and access is not as big of an issue by going stringless. I’ve been really impressed, and now I can’t imagine working without it.”
Scott Preston, Paving Superintendent on one of the GOMACO GHP-2800 with IDBI attachment paving spreads, was a dedicated stringline user. The I-15 was his first experience with a 3D system.
“At first, it was tough to get used to something that I’d never run before because I was just so used to stringline,” Preston explained. “We’ve really been able to make the system work to our best advantage with the time line of the schedule. They’ll switch traffic and move the safety barrier the night before and we’re able to come in and pave the next morning with the 3D system. Otherwise, you’d have a day of preparation just to set up the stringline. It’s also great for truck hauls. We’re able to run the trucks a lot tighter to the paver and get better production out of our trucks instead of having to reroute them around our stringline.
“I’ve really come to enjoy 3D paving. We’re able to pave a lot more safely by eliminating hazards with guys walking and truck travel, and we have a lot more room around the paver to do the things that we need to do.”
Each paving spread is assigned two 3D personnel for each pour. It’s their job to set up the 3D system before every pour, and then leap frog the total stations during the pour. Five total stations are used during paving. Three work with the paver and are set up at 200 foot (61 m) intervals, 7.5 feet (2.3 m) away from the track line. Two total stations work with a Leica rover for grade checks.
“One of our biggest challenges has been keeping seven pavers going with four systems,” Trane said. “We’re able to move the Leica computers rather easily and it’s just a matter of plugging that computer into the GOMACO controller on the paver. It’s an easy swap to make.
“We use Leica to control everything the paver does... take it up a ramp, take it around corners, and even take it around a corner on a ramp. Just build it into the model and you can make the paver do whatever you want. I’ve done string for 10 years prior to this project, but I love the stringless. I like the control you get with Leica and we’re getting great rides with the system.”