Tunnelling guru Martin Herrenknecht speaks out on the importance of Crossrail to Britain’s economy, infrastructure to the world at large and the role tunnel boring machines play. Margo Cole reports.
Tunnel guru Martin Herrenknecht is keen to see London’s Crossrail project move forward. This is perhaps not surprising, given that the company that bears his name must surely be one of the front runners to supply tunnel boring machines to the project.
The company was last seen in the UK when two of its machines dug the twin bore tunnel beneath the Thames for High Speed 1, so it knows a thing or two about the tricky ground conditions under the capital.
But Herrenknecht’s interest in the project is not entirely selfish. “The country that has the best infrastructure will have the best future,” he told NCE on a recent visit to London. “That’s why Crossrail is important.”
The infrastructure he’s talking about ranges from road and rail projects to alleviate congestion in cities like Berlin, Moscow and London to water supply schemes in the Middle East, China and Australia. And climate change is playing its part, with the need to find ways of coping with floodwater in areas like the Far East, and ways of limiting our dependence on air travel.
“A situation that is going to be pushed much stronger is this issue of not going on aeroplanes, but using fast trains instead,” says Herrenknecht. “There will be a discussion about this here in England like there is in Germany and in France.”
He cites Switzerland’s Alp-Transit project as an example. The SwFr16bn (£9.8bn) statefunded project involves building base tunnels beneath the Alps to create flat, high speed northsouth rail routes through the country.
The longest of these (and the longest rail tunnel in the world), the Gotthard base tunnel, will help cut travel time between Zurich and Milan from fours hours to two and a half hours.
Although Herrenknecht is best known in the UK for its earth pressure balance and slurry shield machines for soft ground, the firm has made a successful move into hard rock tunnelling in recent years, and last month its Gabi 2 gripper tunnel boring machine (TBM) completed a 7.2km section of the western tube of the Gotthard base tunnel six months ahead of schedule. Two months earlier Gabi 1, its sister machine, broke through on the eastern tube.
The TBMs on that project are 9.58m in diameter, and excavated an average of 18m a day in hard rock with overburdens of up to 1km. Gabi 2’s best daily performance was 56m of excavated and secured tunnel - a worldrecord for a TBM of this size.
But these machines were quite small in comparison to some the company has produced. In 2006 Herrenknecht supplied two 15.43m diameter “Mixshields” to excavate two 7.47km long parallel tunnels beneath the Yangtze river in Shanghai, China - the largest TBMs ever produced. And there are plans for a 19m diameter TBM to create a four-lane highway to alleviate congestion in Moscow, once the economy picks up.
Mixshields are dual mode machines that can be quickly converted from one mode to another if the ground conditions change - making them ideal for complex geologies where ground conditions vary over the length of the drive, especially if water is anticipated. It was Mixshields that the firm supplied for the High Speed 1 tunnels, wherethe excavation went through alluvium, chalk and flint beneath the Thames. Herrenknecht credits the success of the project in part to the integrated cutter wear detection system incorporated within the TBM. This made it possible to monitor the degree of wear of the cutters and plan when they should be changed.
The company has been developing Mixshields that can be converted to any type of operation mid drive so that all combinations of slurry, earth pressure balance shield, compressed air or open shield methods are possible. “When we started the Mixshield 15 years ago it was used first in the Grauholz tunnel in Switzerland,” recalls Herrenknecht. “The ground changed from hard rock to gravel, so we converted the machine from hard rock to slurryshield. At that time it took three weeks to change over - now we can do it in two shifts.”
In addition to the wear detection system, the machines can also be fitted with seismic probes, which send out highfrequency waves. By analysing the return signal, the operator can calculate the location of large stones. This helps with the steering and with deciding if the set-up of the machine needs to be changed or whether different cutting tools should be fitted.
Cutters on the firm’s latest machines can be changed from behind the cutterhead. This is quicker than sending someone out in front of the machine, and safer, as it means the change can be done at atmospheric pressurerather than in compressed air.
The flexibility these latest machines offer is likely to be more important than ever in the tunnels of the future. Many of these are bound to be in areas that have not been developed yet because of poor ground conditions, or in countries where TBM tunnelling is still in its infancy.
“There are likely to be more complicated projects in the future,” says Herrenknecht who, at 67, has no plans to retire. “I like that challenge.”
Martin Herrenknecht CV
1942 Born Lahr, Germany
1964 Graduates from University of Konstanz with professional engineer degree
1964 First job, with Swiss firm Ammann, as design engineer for road construction machinery and vibration drums
1971 Appointed director of mechanical engineering at Huttegg, part of the Seelisberg tunnel project in Switzerland
1975 Launches first company - the engineering service company Martin Herrenknecht, in Lahr
1977 Launches Herrenknecht Tunnelling Systems
1993 Receives Bundesverdienstkreuz am Bande (order of merit of the Federal Republic of Germany)
1998 Receives honorary doctorate (Dr Ing) from the Technical University Carolo-Wilhelmina, Germany
2002 Awarded first Karlsruhe Innovation Award for Construction Endeavours, by Karlsruhe University (Technical Institute)
2007 Receives Cross of Merit, First Class, of the Federal Republic of Germany
2009 Member of the Handelsblatt Hall of Fame for German entrepreneurship
In 2006 Herrenknecht supplied two 15.43m diameter tunnel boring machines (TBMs) to China for the construction of twin 7.47km long tunnels, running from Changxing Island to Pudong in Shanghai.
The tunnels will alleviate traffic congestion in the rapidly expanding city. The tunnels have to be open to traffic in time for the World Expo in 2010.
The tunnels are located at a depth of up to 65m in groundwater-bearing sand, clay and broken rock formations. When finished, they will have two levels. The upper deck will be used as three-lane road tunnel and the lower deck will be a service and rescue tunnel. The long-term objective is to also use the lower deck for metro traffic by integrating the Shanghai Rail Transit Line 9.
The two Mixshield machines started tunnelling between Pudong and Changxing Island in September and December 2006. Each TBM weighed 2,300t and measured 135m in length. They each had a cutterhead with six cutting wheel arms that could be accessed via the rear of the shield under atmospheric conditions - allowing for cutter changes under extreme conditions while maintaining safety.
The TBMs excavated two tunnels 23m apart - measured between centre axes - and operated at a pressure of up to 6.5 bar. At peak, each machine excavated 26m in a day. The first machine broke through in May 2008, a year earlier than scheduled, after a construction period of 20 months. The second reached its target in September 2008, 10 months ahead of schedule.