Subterranean transformation: reunifying Germany's transport system30 August 2012
As part of the ongoing German reunification transport infrastructure project, known as Verkehrsprojekte Deutsche Einheit, the new rail route between Erfurt and Leipzig includes three recently constructed tunnels. Urban Transport Agenda talks to project leader Marcus Schenkel about the mix of tunnelling methods deployed, mitigating the environmental impact and meeting other age-old excavation-related challenges.
Affectionately known as 'the green heart of Germany', the region of Thuringia, located in the centre of the country, is defined by its dense forests and rolling plains. To the north-west, the Finne ridge of hills, which peaks at 380m above sea level, stretches into the adjacent state of Saxony-Anhalt.
But, while this verdurous hinterland appears as tranquil as ever, below the swathes of pine and fir trees, it is in the process of undergoing a substantial subterranean transformation by dint of the construction of a new 6,970m tunnel cutting across the landscape.
The Finne Tunnel is the first - and longest - of three dual-tube tunnels found along the 123km electrified rail track from Erfurt to Leipzig, set for completion in 2015. The line forms part of the extant German reunification transport infrastructure project Verkehrsprojekte Deutsche Einheit (VDE), the country's most expensive and ambitious transportation project to date.
Boring through the landscape
Conceived in the wake of the fall of the Berlin Wall, VDE will ultimately see the assembly of a 500km high-speed railway line between Berlin and Munich, with trains scheduled to start running in 2017. Track speeds are set to reach 300km/h, slashing the overall journey time between the two metropolises from six hours to four.
The installation of tunnels is vital if the trains are to reach the proposed levels of velocity. By boring straight through the landscape - as opposed to laying down tracks along its contours - track curves and inclines are eschewed, in turn allowing both commercial and freight trains to remain at uninterrupted high speeds.
Overseen by Deutsche Bahn, Germany's national railway company, the Finne Tunnel, along with the Bibra (6,466m) and Osterberg (2,082m) Tunnels - which together come to a total length of 15.4km as part of the latest VDE 8.2 line - have been constructed using an amalgam of traditional excavation methods and state-of-the art tunnelling technology.
"We used a combination of methods," says VDE 8.2 project leader Marcus Schenkel. "The Finne Tunnel was the only one of the three to be constructed entirely by machine. Given the incorporation of two inner tubes, this required the use of two tunnel-boring machines working in tandem, manufactured specifically for the project. Then the space created by the machine was immediately converted into a tunnel tube using prefabricated concrete segments."
In December 2006, work began on the Finne Tunnel, which, as Schenkel admits, proved to be the "trickiest of the three". The main challenge for miners came in having to bore into the area's highly disjointed rock formations, constituting both loose and hard rock. In order to combat this, hydroshield/hard-rock tunnel-boring machines were used, along with disc cutters to apply additional pressure to the rock mass.
Conversely, the Bibra and Osterberg Tunnels were mainly manufactured using traditional dynamite earthwork techniques, in which the inner tubes were fashioned through smaller steps comprising drilling and blasting.
"These methods were really dependent on the respective geotechnical conditions," explains Schenkel. "So, as well as heading machines, we made use of explosions and tools such as jackhammers."
In addition to tackling disparate rock formations - marl, limestone, dolomite rock and siltstone are just some of the types of rock endemic to the region - another major stymie for excavators and miners across the three tunnels concerned the management of excess water. This was mainly combatted through the use of high-end technology in the form of liquid-supported hydroshield machines.
"The management and handling of water certainly posed an issue, as excess water has the ability to jeopardise projects," he says. "As well as machinery, we also constructed bore wells with depths of up to 80m. Moreover, you really need to have an understanding of the geological surroundings before you start tunnelling and track construction. We spent a lot of time looking into this."
Keeping Germany's heart green
As Schenkel infers, a geological and hydrological vetting process was conducted before initial construction. Preliminary investigations involved the analysis of aerial photographs, and the deployment of pulse echo technology and 100m-deep bore holes in order to explore the subterranean conditions - "the main challenge with tunnelling is that you never know exactly what you will find," he says.
In order to obviate the risk of encroaching on the surrounding natural environment, efforts were also made to be as environmentally conscientious as possible - even more pertinent given that parts of the Finne are listed as nature reserves. And with dynamite excavations and earthworks long associated with harsh chemicals such as ammonia compounds, levels and procedures were closely monitored and recorded in order to mitigate potential risks.
"When the bones of the reunification project were first laid out in 1991, the environmental impact of the construction was made a priority," recalls Schenkel. "Luckily, I would say our experiences have been relatively problem-free.
"This also goes for noise pollution. We made sure to measure noise development during excavation using dynamite and then documented the results. We were careful to stick to the limits stipulated by environmental protection laws at all times."
Furthermore, an onus was placed on recycling surplus excavation materials, which were transported out of the tunnel via jaw crushers, pumps and conveyor belts, and strategically deposited close to the tunnel portals
for landscaping purposes.
"All excavated materials were reintroduced into the surrounding landscape," says Schenkel. "We also kept the materials close to the construction site in order to save on transport miles. In fact, I would estimate that 20-30% of materials went into other construction areas for the next part of the track."
Despite some "initial logistical concerns", Schenkel claims that, overall, the construction of the three tunnels was fairly unproblematic, with miners encountering few major hindrances - "the erection of the bridges has proven to be far more exacting," he says.
A major consideration for Deutsche Bahn, however, concerned the acclimatisation to an ever-evolving raft of safety regulations set out by the EU. Namely, this related to the obligatory implementation of cross-passage rescue tunnels, as Schenkel explains.
"The real challenge for us was not the actual tunnelling so much as getting European approval for the safety aspects," he says. "And these regulations are still changing. For example, the initial project guidelines declared that, for the two tubes within the tunnel, additional rescue tunnels equipped with lock systems were required every 1,000m. During the construction period, this was altered to be at 500m intervals.
"As you can imagine, if you have a tunnel with prefabricated parts, this presents difficulties as it is very difficult to implement these changes, especially if you are 50m above the tunnel. This is a problem still facing other parts of the VDE project."
Funded by the German Government, the EU and Deutsche Bahn, the earthworks alone for the Erfurt-Leipzig section of the track are estimated to have cost in the region of €30 million. At the time of writing, work has moved onto the construction of concrete tracks. "The tunnels are more or less finished," says Schenkel.