A height tolerance 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 +/- 0.1 in. (3 mm) by far outperformed the required accuracy of a maximum +/- 0.4 in. (10 mm)," said Baumgartner.

In total, 36,623 cu. yds. (28,000 cu. meters) of concrete was slipformed in each 4.3-mile-long (7 km) tunnel to build the tunnel floor. Both production and quality of the finished product exceeded expectations.

100% Accuracy Required

The second phase of slipforming involved Wayss and Freytag converting the Commander III to a three-track paver to slipform a walkway against one wall of each tunnel.

"The line of the train track must be 100% 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 and built a variable-height, variable-width walkway mold and hopper to accommodate the varying line of the tunnel. 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 meters) up to 5.7 ft. (1.75 meters). Height of the walkway was also variable from 23.6 in. (600 mm) up to 37.4 in. (950 mm). 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 hand finishing.

A service channel in the surface of the walkway profile was slipformed 3.3 in. (85 mm) wide by 2.8 in. (70 mm) 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 2% 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% 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 meters) per day."

Wayss and Freytag was on schedule to complete its portion of the Finne Tunnel by the end of 2011. 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.