The country of Slovakia is currently undertaking a massive road-building project to improve transportation within its borders and to surrounding countries. Slovakia is located in central Europe and borders the Czech Republic, Austria, Poland, Ukraine and Hungary. Part of the effort to improve transportation is centered around Motorway D1, running from east to west through the country.
It is currently 259 km (161 mi) long, but new construction in the next five years or more will increase it to 517 km (321 mi) in length. Doprastav, a.s., based out of Bratislava, Slovakia, is in charge of constructing segments of the new motorway, which includes a concrete safety barrier.
The company operates a GOMACO GT-3600 for curb and gutter work on their projects, and were looking for another GOMACO machine to slipform the 1100 mm (43.3 in) tall barrier. Once again, they chose the GT-3600, this time equipping it with a Leica PaveSmart 3D system for stringless barrier paving.
“We have a lot of experience with the GT-3600 by producing curb and gutter of various dimensions,” Jozef Vondál, Producing Manager of Doprastav, said. “We decided to start slipforming barrier wall in May 2006 because we saw that it would give us more production and allow us to be more effective.”
They put their new GT-3600 with stringless system to work on a 4 km (2.5 mi) long section of the new motorway by Zilina, connecting Vrtizer to Hricovské Podhradie. The barrier wall has a 685 mm (27 in) wide base and is 1100 mm (43.3 in) tall. Four 15 mm (0.6 in) diameter steel cables have to be inserted through the front of the barrier mold for reinforcement in the wall.
Incorporating the stringless guidance system into their project requires just a few steps. The engineer’s design data for the project is converted into a surface model. That model is loaded into the Leica computer mounted on the GT-3600. The Leica computer is interfaced with the GT-3600’s G21 controller.
At the start of each day, the GT-3600 is moved into position. The three Total Stations used on the project take measurements off predetermined reference points to orientate their position. They are then aimed at the prisms on the GT-3600 and they begin the tracking process. The Leica computer immediately can tell whether the machine is positioned correctly and everything is set accordingly before slipforming the barrier wall.
Barrier wall requires careful machine control to keep the wall from collapsing in any conditions. The Leica PaveSmart system uses the Total Stations and slope sensors to continuously calculate the position, height and orientation of the machine as the GT-3600 slipforms the barrier wall. It automatically regulates all points of the machine relative to the project’s 3D design data.
One Total Station is constantly measuring the front prism on the GT-3600 and is controlling the steering for the front of the machine. The second Total Station measures the rear prism and controls the steering and elevation on the back of the GT-3600. A dual-axis slope sensor on the GT-3600 also allows the slope of the machine, from front to back and side to side, to be constantly monitored and controlled.
The third Total Station is used for as-built checks and provides instant feedback regarding the accuracy of the new wall. The third instrument is also used for leap frogging. The Total Stations have a typical working range of 200 meters (600 ft) and a tracking accuracy of 3 mm (0.1 in) at 100 meters (300 ft).
The system is more accurate than traditional stringline, saves time, and allows for an open job site. Stringline is no longer required, so lines don’t have to be measured out and set. Workers on the project don’t have to worry about bumping the line or something happening to it that would cause an error in the slipforming. With no stringline to set, Doprastav can move anywhere around the job site. If one area is not ready to be paved, they can simply move the machine to a different area, orientate the machine to its location on the project, and begin slipforming wall.
The concrete mix design also has to be factored in for good barrier wall. Doprastav worked closely with their concrete supplier to develop a barrier mix. They took a standard concrete slipform mix design and added aerating ingredients. Slump averaged 20 mm (0.8 in).
Average production on the barrier wall was approximately 250 meters (820 ft) per day, with concrete supply being the limiting factor.
“Production is dependent on how well the concrete delivery is coordinated and once the concrete arrives, if the appointed mix design has been observed,” Vondál said. “Once we have the right concrete, the GT-3600 works well and is very smooth and fluent.”
Very little finishing work has to be done behind the GT-3600. Joints are saw cut into the cured wall every four meters (13 ft).
Doprastav’s GT-3600 will continue to work on the D1 Motorway in the future. They have been awarded the contract to build the next section of the roadway as the country of Slovakia continues to improve its major thoroughfares.