Tunnelling for European high-speed railways

Since the 1980s railway traffic for passengers has experienced a renaissance. Especially France and some time later Germany started to construct and operate their first high-speed lines with speeds between 300 and 350km per hour. Later, other European countries followed; such as Italy, Spain and the UK, and even the Alpine countries with an extremely difficult topography.

The history of modern heavy railway systems began in Europe for passenger transport in 1830 with the line between Liverpool and Manchester in the UK. Soon afterwards, the continental countries followed and introduced the British system in their areas, for example Germany in December 1835 between Nuremberg and Fürth using the famous Stephenson Locomotive ‘Adler’ (‘Eagle’) applying the British gauge of 1,435mm. During the following few decades a real boom in constructing railways was seen.

In parallel to the construction of railway lines, it was not long until the first tunnels had to be built applying the historical tunnelling methods using plenty of wooden supporting material and excavating in several parallel partial drifts. Taking Germany as an example, the first tunnel was 1,620m in length and was constructed in 1837/38. In 1850, 21 tunnels were already in operation. This figure rose in 1860 to 68 tunnels and in 1870 approximately 138 tunnels. During the following decade, until 1880, an additional 157 tunnels were constructed with a total length of 65km. The average length of the tunnels was relatively small. In 1880, approximately 300 operated railway tunnels resulted in a total length of 114km₂.

Today, modern high-speed railway lines, in comparison to older railway lines, need significantly more tunnelling. This is due to the necessity to keep the lines as straight and as flat as possible to make operating with speeds of 300 to 350km per hour possible, both from the physical and the economical (energy consumption) point of view. In some of these recently built lines, the percentage of tunnels related to the entire stretch equals 30 to 40% and in extreme cases even significantly more. This of course raises the investigation costs of those high speed lines tremendously. Nevertheless, the various countries take that enormous economical effort to replace air travelling on short distances, to attract automobilists, to accelerate passenger traffic and to improve by that the politically highly ranked mobility of persons. At the same time they contribute by those measures to a better protection of the environment.

TEN-T

Jaques Barrot, Vice-President of the European Commission, with responsibility for transport, once stated3 that modern economies cannot generate wealth and employment without highly efficient transport networks. This is particularly true in Europe where, for goods and people to circulate quickly and easily between Member States, we must build the missing links and remove the bottle-necks in our transport infrastructure. The Trans-European Transport Network is a key element in the re-launched Lisbon strategy for competitiveness and employment in Europe for that reason alone: to unblock major transport routes and ensure sustainable transport, including through major technological projects.

All in all, 30 priority axes and projects are listed₃ and together they form the Trans-European Transport Network (TEN-T) which places a crucial role in securing the free movement of passengers and goods in the European Union. It includes all modes of transport and carries approximately half of all freight and passenger movements. By 2020, TEN-T will include 89,500km of roads and 94,000km of railways, including approximately 20,000km of high-speed rail lines suitable for speeds of at least 200km per hour. Completing the network by 2020 involves the construction of the so-called ‘missing links’, increasing the existing road network by 4,800km and rail by 12,500km. In addition, approximately 3,500km of roads, and 12,300km of rail lines will be substantially upgraded.

The 30 priority axes mainly involve railway lines. Among them are important ones such as the north-south link from Berlin-Verona/Milan-Bologna-Naples-Messina-Palermo, including the Brenner base tunnel or the high-speed railway axes from Paris-Brussels-Cologne-Amsterdam-London, and the high-speed railway axes of south-west Europe from Salamanca/Porto-Lisboa-Madrid-Paris/Lyon. Other major railway lines within TEN-T include the railway axes from Lyon-Torino-Trieste-Ljubljana-Budapest including the Mont Cenis-base tunnel, the West Cost Main Line in the UK from Glasgow/Edinburgh-Liverpool-Birmingham-London, the Fehrman Belt railway axes from Kopenhagen-Fehrman Belt-Hamburg-Hannover or the railway axes from Athens-Sofia-Budapest-Vienna-Prague-Nuremberg/Dresden.

Some of these lines are already under construction and involve major tunnelling activities.

Major tunnelling projects

For modernising, upgrading, and accelerating the most important European railway links, several longer and extremely long railway tunnels in various European countries are already under construction or atleast in the design stage. Table 2 gives an idea in this direction.

Nearly all tunnels listed in table 2 are designed as two parallel single-track tunnels excavated by using a TBM (tunnel boring machine). The excavation diameter is chosen in most cases between 9 and 10m. An extreme is given with the Groene Hart Tunnel in The Netherlands with an excavation diameter of 14.8m for a double-track tunnel.

Before going into details with one or the other project, in general the following can be stated (Herrenknecht, Thewes₁): During the last 10 to 15 years, mechanised tunnelling using shield machines has been characterised by the introduction of a large number of innovations, by means of which the tunnelling industry has been able to react to increasingly more sophisticated field conditions. Derived from the Olympic motto ‘Citious – altius – fortius’, developments in tunnelling can be described with the words ‘faster – larger – deeper – longer’:

• Faster: rates of advance in problematic subsoil (e.g. abrasive or clogging) were substantially increased
• Lager: shield machines with diameters in excess of 15m were built
• Deeper: locations down to 60m in permeable, soft ground carrying groundwater were exploited
• Longer: about two thirds of the work on the 57km Gotthard Base Tunnel, the world’s longest, has been completed mostly using TBMs

New yardsticks for the driving technology that had to be applied were set for a large number of major tunnelling projects. This led to the development of a catalogue of ancillary measures and equipment, which can be made use of if required e.g. in the event of tricky geological or hydro-geological conditions. As a consequence, it was possible to extend the fields of application for shield machines and problematic part-sectors successfully mastered.

The development in this direction is not yet finished so let’s expect an ongoing increasing part of the entire tunnelling volume conducted by the application of TBMs.

The progress in using a TBM for the excavation of a longer railway tunnel will be described in the following by three examples:

1. Guadarrama railway tunnel – part of the high-speed railway route between Madrid and Segovia, Spain
The 28.4km long Guadarrama Tunnel passes through unweathered gneiss, granite-like and partially weathered rock. Herrenknecht supplied two double shield solid rock machines for the 2x 14.5km long excavations with maximum overburdens of up to 2,000m. The two TBMs with 9.51m boring diameter are adapted to the project-specific conditions, e.g. the geological and logistical circumstances. The two identical double shields are numbered among the technically most sophisticated machines in tunnelling as two application principles, shield TBM and gripper TBM, are combined in one. When entering geological fault zones, the shield adapts relatively quickly to the given geology, without any major losses in the rate of advance having to be accepted. This machine concept facilitates safer working conditions and continuous excavation.

2. Lötschberg and Gotthard Base Tunnels, Switzerland
A total of four TBMs are being used to produce the major rail route crossing the Alps between Germany and Italy. The tunnel routes pass through rock with high compressive strength and abrasiveness with in some cases, zones with boulders present at the face. 2 Gripper TBMs with a diameter of 9.43m were used for the Lötschberg Base Tunnel project. The cutter head was equipped with 60 17inch cutter rollers. The cutter head shield was kept very short so that the ground could be secured all-round as soon and as close to the cutter head as possible. In addition, the steel mats (permanent protection overhead) can be installed immediately behind the short cutter head shield. The findings gained in the tricky geological conditions during the two tunnel drives at the Lötschberg were included in the innovative concept for the four solid rock machines for the Gotthard Base Tunnel. The TBM has as smooth cutter head for necessary penetrating blocks of rock – with cutter roller holders set flush with the cutter head structure. The cutter rollers are incorporated in the cutter head steel construction by means of the roller bit housing and can be replaced from the rear section. As a result, the cutter head concept also facilitates the installation of the roof support close to the face. The design of the machines for the Gotthard Base Tunnel sets new standards with respect to attainable tool changing times. Accessibility of the cutter rollers was further optimised in order to minimise standstill times for changing tools.

3. Katzenberg Tunnel, Germany
Deutsche Bahn AG is engaged in upgrading the so called Rheintalbahn between Karlsruhe and Basle from a 2-track route to a continuous 4-track route. The route is part of the Trans-European Network (TEN) which is of high international significance and serves as the main access line to the Gotthard Base route in Switzerland which is currently also under construction. The largest individual structure along this route is the 2-tube Katzenberg Tunnel with a length of 9.4km, on which 9km are produced by TBM drives. The tunnel is designed to cope with trains travelling at speeds of up to 300km/h. The maximum overburden amounts to 110m. Apart from quaternary covering layers at the tunnel’s entrance zones, mainly tertiary sedimentary rocks such as mudstone, schluff and occasionally sandstone in varying stages of weathering were encountered during the exploration phase. The rock strength is low. In the southern tunnel section Jura massive limestone formations have to be penetrated over a length of some 800m. Filled karstified structures that present no problems in tunnelling terms are expected especially in the transition zones to the tertiary. The TBMs were assembled in the pre-cut. The first machine started operating in the eastern tube in June 2005.

Closing

The history of railways began in the first third of the 90th Century. Since the last two to three decades, the railway traffic has experienced a renaissance mainly indicated by the construction and operation of ultra-modern high speed lines. These new lines ask for an as straight and flat alignment as possible both from the physical and the economical point of view. Against this background, many tunnels have to be constructed along the high speed lines especially if they cross upland ranges or even Alpine chains. The length of those tunnels and the sometimes extreme overburdens are linked with real challenges for the tunnelling industry. All the efforts taken by the various European States contribute significantly to a faster and more reliable transport infrastructure and thus ensure better preconditions for a higher mobility both for persons and goods in the European community.

REFERENCES

1. Brockhaus Enzyklopädie, 19th edition 1988
2. Haack, A.: Underground Construction Germany 2005, published to mark the STUVA-Conference ’05, Leipzig, by the STUVA – Studiengesellschaft für unterirdische Verkehrsanlagen e.V., Cologne and the DAUB – Deutscher Ausschuss für unterirdisches Bauen e.V., Cologne
3. Trans-European Transport Network: TEN-T priority axes and projects 2005; European Commission’s Directorate General for Energy and Transport, Brussels, 28 July 2005