A massive construction project has been underway deep in the heart of the Schnecktal valley area in Germany. From the surface, though, you would never be able to tell. The majority of the work is underground as a joint-venture team led by German contractor Wayss & Freytag Ingenieurbau AG builds the nearly 4.3 mi. (7 km) long Finne Tunnel. After a few years of tunnel boring operations, the contractor is at work finishing the interior of the tunnel, slipforming first the tunnel’s floor and then a walkway with its GOMACO Commander III.
Finne Tunnel is just one section of a new 76 mi. (123 km) high-speed rail link between the cities of Leipzig and Erfurt, Germany. Initial construction on the twin-bore tunnel began in April 2008. Two tunnel boring machines (TBMs) worked at the same time boring the 35.4 ft. (10.8 m) diameter shafts. Peak TBM production rates reached up to 80 ft. (24.5 m) per day.
The high-speed trains traveling along the new route will reach speeds up to 186 mi./hr. (300 km/hour), capable of exerting huge pressure waves within the tunnel walls. Such high speeds and resulting pressure waves dictated the large external diameter of the tunnels. The internal, lined diameter is 31.5 ft. (9.6 m) and was formed using precast concrete lining segments or rings. They were cast onsite and each ring was 6.6 ft. (2 m) long, 17.7 in. (45 cm) thick and weighed 12 tons. A total of 6822 rings were needed to line the new tunnels.
In September 2009, the first TBM “holed through.” The second one followed it a few months later when it broke through in February 2010, six months ahead of schedule. Work was far from being completed, though.
“Because of the sequence, we were left with two circular pipes nearly 4.3 mi. long rather than tunnels,” Gerhard Baumgartner, Segment Engineer for the Joint Venture said.
It was time to start the slipforming phase within the tunnels. Representatives from Wayss & Freytag worked with GOMACO International Ltd. to determine which paver would suit their tunnel applications. They chose the GOMACO Commander III. The Commander III would first pave the tunnel floor in four-track mode. Then, it would be converted onsite to a three-track paver to slipform the tunnel’s walkway.
The decision also was made early in the design phase to use the Leica Geosystems 3D control system. Setting and maintaining stringline within the tight confines of the tunnel would be nearly impossible, and the stringless system would alleviate those concerns.
The concrete for the various tunnel applications was provided by an on-site mobile batch plant with a 105 cu. yd. (80 cu m) per hour capacity and is located just outside of the tunnel entrances. They produced a dry, low slump concrete with a low percentage of cement.
“We had concrete with less cement because of the size and depth of the applications,” Christian Korndörfer, project manager of Wayss &?Freytag, explained. “The floor is over 3.3 ft. (1 m) thick. We didn’t want the concrete curing process to generate too much heat inside the tunnel or result in any cracking within the concrete.”
Delivering concrete to the Commander III within the circular tunnel also was a concern that needed to be addressed before paving could begin. Wayss & Freytag wanted to use standard concrete trucks, but having them drive in reverse through the length of the tunnel to reach the paver would be too time consuming. There also was no room inside the tunnel for trucks to turn around.
They developed a two-part solution. The floor of the tunnel was paved in a special sequence. A weekly paving production goal of 3,281 ft. was established, with an average paving goal of 820 ft. (250 m) per day. At the beginning of each week, the four-track Commander III was set up to pave 3281 ft. (1000 m) beyond the section of floor completed the week before. The concrete trucks drove in forward gear on the completed tunnel floor to a turntable at the end of the section. The turntable then rotated the three-axle trucks 180 degrees so they could drive in reverse to the paver, dump their load of concrete in front of the Commander III, and then drive out of the tunnel in forward gear. Between six to eight trucks carrying 10.5 cu. yds. (8 cu m) loads of concrete transported the material to the Commander III.
“The tunnel floor is 19.7 ft. wide,” Korndörfer said. “In the circular tunnel, at its deepest point in the center, the floor was 41.3 in. We turned all four tracks on the Commander III to 35 degree angles so the paver could drive on the round walls.”
The slipform mold was designed for a drainage channel in the tunnel floor. The channel measured 7.1 in. (18 cm) deep and 28.3 in. (72 cm) wide at the top tapering down to 21.3 in. (54 cm) wide at the bottom.
A height tolerance of plus or minus 0.4 in. (1 cm) had to be met on the new tunnel floor to ensure the accurate installation of the future track rail. Control measurements confirmed the new concrete tunnel floor was always within the specified height tolerances.
“The achieved vertical accuracy of plus or minus 0.1 in. by far outperformed the required accuracy of a maximum plus or minus 0.4 in.,” said Baumgartner.
In total, 36,623 cu. yds. (28,000 cu m) of concrete was slipformed in each 4.3 mi. (7 km) long tunnel to build the floor of the tunnels. Both production and quality of the finished product exceeded expectations.
The second phase of slipforming within the Finne Tunnel project involved Wayss & Freytag converting their Commander III?to a three-track paver to slipform a walkway against one wall of each tunnel. GOMACO built a variable height, variable width walkway mold and hopper to accommodate the varying line of the tunnel.
“The line of the train track must be 100 percent accurate and its placement is considered sacred,” Korndörfer said. “The walkway mold had to be able to accommodate the changing alignment of the tunnel, tunnel superelevations and other variations created when working inside a tube.”
GOMACO engineers designed the mold and hopper with telescoping abilities. As the face of the tunnel wall changed, the mold compensated by telescoping in and out or up and down to change the size of the walkway and keep the profile in correct alignment to the train tracks. The telescoping feature also ensured the mold was always kept against the tunnel wall and the accuracy of the walkway placement maintained.
The top width of the walkway varied between 3.4 ft. (1.05 m) up to 5.7 ft. (1.75 m). Height of the walkway was variable also, from 23.6 in. (60 cm) up to 37.4 in. (95 cm). Hydraulic pressure-compensated cylinders controlled the changes.
A finishing roller, mounted to the back of the mold, helped provide the finish to the walkway’s surface and eliminate the need for handfinishing.
A service channel in the surface of the walkway profile was slipformed 3.3 in. (8.5 cm) wide by 2.8 in. (7 cm) tall. Lighting conductor strips will eventually be placed in the keyway, tested to make sure they are operational, and then covered and sealed. The keyway allows the strips to be removed and replaced as needed without damaging the profile of the walkway. A two percent cross slope across the top surface ensures proper water drainage off the walkway.
“The walkway was a much more challenging profile to slipform than the tunnel floor,” Korndörfer explained. “It had to be placed with 100 percent accuracy and the Commander III slipformed the walkway very well. We had no problems and were able to achieve production rates from 558 to 656 ft. (170 to 200 m) per day.
“The problem with the tolerances in the walkway and the need for the walkway mold to change size was one of the biggest challenges we faced on the project. Our other challenge was the logistics of getting concrete into the tunnel. We were able to devise solutions for both problems and achieve a quality product. Our GOMACO with the Leica system has done a good job and worked well.”
Wayss & Freytag is on schedule to complete their portion of the Finne Tunnel by the end of this year. Other contractors will then start work placing the track and installing the electrical and other systems.
The entire Erfurt to Leipzig line will be operational in 2015 and will be part of a high-speed connection from Munich to Berlin, Germany. Ultimately, the line will run all the way from the countries of Scandinavia to Italy.
This article was republished with permission from GOMACO World Magazine, Volume 39, Number 2.
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