Boring the Longest Tunnel for EU's High-Speed Rail

In due time, considerable time will be saved on the train ride between Munich and Berlin. With the ride taking less than four hours, the rail link will be a viable alternative to domestic air travel.

This railway connection will be a section of the grander European Union's Trans-European Networks (TENs) connecting Italy and Scandinavia. The TENs are large infrastructure networks of transport, energy and telecommunications underpinning the developmental and integration goals of the European Union, which includes the "free movement of people and goods" among the whole union of 27 member states.

Listed in the German Federal Transport Plan as Unity Rail Project No. 8.1, the high-speed link between Munich and Berlin traverses tough terrain. Half of the stretch will require nels, viaducts and bridges – the highest proportion yet for a new rail line in Germany.

One significant nel is the Blessberg nel, which at 8,314 m will be the longest. A contractor consortium, called ARGE nel Blessberg, was formed to perform the challenging blasting and bore work. The group consists of STRABAG AG, Züblin AG and Bickhardt Bau AG. Work commenced November 2006.

After the nel blasting began, around 40-60cm of undercut accumulated. It is being removed using a Wirtgen W2200 milling machine on a distance of 4km. The milling operations were subcontracted to Kutter GmbH & Co. KG, a leading milling contractor in Germany. The milling work, which started in early summer 2008, relied on the conventional built-in laser control system. Even with 24-hour work shifts, the progress was slow and tedious. At issue were the number of curves and changing slopes included in the nel design. The vast amount of dust produced created limited visibility, which meant workers had to re-establish the laser at a maximum of 50m intervals. Two people were assigned full time just to take care of the laser set-up and checking. One thing became clear, the laser solution was proving to not be practical in this tough environment and was becoming too costly to operate.

Wolfgang Mötzung, site supervisor at Bickhardt Bau AG, pursued a solution. He was familiar with the Trimble® 3D Grade Control Systems and their effective use on other construction machines and applications. Mötzung approached the local Trimble distributor, Lange & Siller, to see if there might be a solution that could work with the Wirtgen milling machine, knowing that there will be no satellite signal reception in the nel.

Lange & Siller recommended a complete Trimble machine guidance system using a Trimble SPS930 Universal Total Station. The Trimble interface box connected to the Wirtgen through the machine's control panel, allowing direct access to the operating valves. The machine-guidance capable total station is designed to constantly calculate the height and cross slope of the drum, guarantying that the required precision is achieved.

The actual Trimble MT900 Machine Target prism position on the milling machine is measured by the Trimble SPS930 Universal Total Station, which is transmitted to the on-board computer, the Trimble CB430 Control Box, which is compared against the nel-bore design. High-accuracy machine-mounted slope sensors provide additional information on the mainfall and cross-slope. Additionally, the Trimble GCS900 Grade Control System regulates the hydraulics, positioning the drum to ensure the design tolerances are met. The machine is controlled without string lines or any other local references; their absence considerably improves the truck and machine logistics on the jobsite and takes away a potential trip hazard.

The operator of the Wirtgen W2200 milling machine can check the position of the drum against the nel design in plan, profile, cross section or text formats instantly and at any time. When performing the final pass the as-built surface can be logged for documentation and quality assurance.

The Trimble patented MultiTrack™ technology of the Trimble SPS930 Universal Total Station also offered a solution to the dusty environment. Even if in the nel the guided machines work behind each other – in this case a milling machine and a dozer operating close to each other - MultiTrack is designed to lock on and track the MT900 active prism constantly, while ignoring environmental obstructions such as heavy dust.

After a short period of testing and evaluation, Manuel Klietsch, responsible for machines and materials on the project for Bickhardt Bau, realized that the 3D approach is showing a number of benefits over the more conventional laser method. The Trimble Universal Total Station extended the working range to 200 – 300 m in one direction. Consequently, this reduced the number of set ups and downtimes of the milling machine to two per day which could be performed by a single person. Thus, there were labor costs savings.

The Trimble technology significantly increased the milling precision to ± 1cm accuracy, compared to ± 4-5cm when using the laser based system. Because the amount of material excavated was reduced, the contractor has less transport and disposal costs.

Consider that an overcut of only 1cm on the complete surface would mean 520m³ of additional material to be transported–the equivalent of 35 more truck loads and transports. Moreover, the 1cm overcut would need to be refilled with gravel resulting in an additional material cost of 15000€ /cm.

Finally, thanks to the high production rate and reduced rework, the milling machine rental cost was reduced substantially.

The ARGE nel Blessberg consortium anticipates completing the massive nel project on time. Completing the Blessberg nel will be significant in connecting Berlin and Munich via high-speed rail. For the intercity travelers on the TENs railway, time will be compressed.