DB-Netz, the operator of German railways (DB) runs about 38,500km of railway lines and their structures. The business is aiming for more rail traffic which can be achieved successfully in the long term only by realisation of increased performances and cost reductions1. Within its strategy, called Network 21, DB-Netz has set up a business-oriented investment programme to be implemented over 10 years. This includes all maintenance works and any new construction, as well as planned improvements. The programme includes many tunnels and other structures, some to be built under difficult conditions.
In order to ensure that these large projects can be realised without unexpected disruption, but within a given budget framework, there is a need to find new approaches, not only for technology, but also for tendering and contract awards, as well as project control. As a result there will be inevitable changes to the usual project procedures for tunnel construction.
New network
The railway network of DB-Netz is classified into priority, performance and regional lines.
Legal basis
In Germany, the federal government finances ‘investments into the railroads of the German federal railways in accordance with the law for the extension of the federal railroads’ within the realms of available funds, and effectively for new construction, upgrades and for investment for replacement.
Furthermore, this law establishes the step-by-step extension of the network in accordance with a ‘plan of demand’, which is an addendum to this law. A component of this is the new construction of the upgrade of railway lines, junctions, new systems for combined railroad traffic, and new inter-modular connections for long-distance traffic to international airports. Aspects of this ‘plan of demand’ are currently being reviewed by the federal ministry of transportation. In accordance with the law, the financing of all projects must be agreed between DB and the federal government in financing agreements.
On the basis of the ‘plan of demand’, a 5-year programme will be established for project realisation by the federal ministry of transportation in close accordance with the proposals of DB. The last ‘plan of demand’ has been replaced with an investment programme for the years 1999-2002 (IP ’99-’02). This programme outlines the measures which have priority up to the end of 2002³.
Projects
DB-Netz is currently working on about 190,000 projects or part-projects, comprising an annual investment of about DM9bn ($4.3bn). The largest current construction projects are the extension of the railway infrastructure in Berlin, the rail-traffic projects called ‘German Unity’ (listed in the federal plan for traffic) and the new high-speed lines (NBS) of Nuremburg-Ingolstadt-Munich and Cologne-Rhine/Main.
Network 21 defines the order of these measures and so describes the position of DB-Netz for the new federal traffic plan. This is under revision at the federal ministry of transportation for the period up to 2015.
Project companies for the execution of large construction projects have been established as wholly-owned subsidiaries of DB-Netz. These are responsible for the preparation and control of the design, planning, execution and supervision of the construction works. Establishment of these companies will achieve a clear assignment of responsibilities, a lean management organisation with flat hierarchical structures and short internal decision making paths.
Taking DB-Projekt GmbH Cologne-Rhine/Main (PKRM), established in 1996, as an example, here is a brief survey of its project and performance.
NBS Cologne-Rhine/Main
There are DM10bn ($4.5bn) at PKRM’s disposal to construct the new 219km-long railway line between Cologne and Rhine/Main. DB-Netz has signed an individual financing agreement with the federal government for the execution of the project which defines the extent of the investment, the sources of finance, the time frame, project descriptions and technical aspects. The project company acts within a project contract of the DB-Netz and handles the project exclusively with all the contractors involved4. Due to its central position the new line is one of the most important transport projects in Germany and Europe. It is to be completed by the end of 2001 and in operation in 2002.
The design, as a 300km/h, passenger transport line, makes possible a route with a grade of up to 40:1000. However, this runs closely parallel to the A3 motorway and needs several structures, due to crossing the low mountain ranges Siebengebirge, Westerwald and Taunus. There will be 30 tunnels with a total length of 47km and 18 valley bridges, total length 6km. Constructon of the tunnels can be costly as the geological conditions are relatively difficult.
The new line is a decisive step towards the integration of transport systems, with the two airports Frankfurt/Main and Cologne/Bonn connecting with DB’s high-speed railway network.
The NBS Cologne-Rhine/Main will be connected to the Cologne/Bonn airport by a 15.2 km-long branch line. This line will be operated with a mix of high-speed (ICE) and local (S-Bahn) traffic. The federal government, the state of North Rhine-Westphalia and the Cologne/Bonn airport authority have signed an individual financing agreement with an additional DM1.04bn ($466M) and entrusted PKRM with execution of the project. The construction contract was signed in September last year by representatives of DB-Netz AG, DB-Station & Service, Airport Authority Cologne/Bonn GmbH and the Public Transport System Rhine/Sieg. Construction work has started to include about 5.5km of tunnels in open cut5.
When the new line starts operating in 2002 many short-distance flights will become superfluous. The relevant agreements have already been signed by DB and German airline Lufthansa.
Tendering procedure
There has been much discussion about tendering procedure, so I would like to limit this to explanations of two different terms:
Whilst the former has proved successful on the Cologne-Rhine/Main project, in our view, some reservations should be made about the use of the latter. In the course of the negotiation procedure, the client is allowed to negotiate on the content of the contract with one or several contractors after the call for tenders. This can lead, in practice, to competitors deviating from their basis for pricing, with the aim of beating the others. Thus there is a risk of distorting the results of the tender. In my view this can lead to an adverse effect on the trust between client and contractor which, to some extent, is necessary in the processing of large, complex projects.
Considering the parameters of ‘limited investment volume’ and ‘tight schedule’ it was decided, for the first time in Germany, to have a railway construction project built ‘ready for occupancy’ on the basis of functional performance. Sections A, B, and C of the 135 km-long intermediate section between Siegburg in the north and the Main crossing in the south were put out to tender all over Europe with a functional tendering procedure. The advantages of this are obvious:
Special attention was paid to the ground investigations for the tunnels relevant to the mining technique. The bidders received a prognosis of the tunnels’ excavation classes with which support measures and excavation procedures have been defined. For each excavation class a standard price per metre had to be given. Also, an additional fee for any additional groundwater and for breaks in operations – not of the contractor’s responsibility – had to be offered.
For a fair distribution of risk between client and contractor, according to VOB C, DIN 18312, the client guarantees the correct description of the ground and rock conditions, whereas the contractor takes the risk of planning and execution8. All work is paid in a lump sum at a defined price; the payment is made according to the construction progress.
Particular care was taken over the correct form of the tendering and awarding procedures on this project, so avoiding objections by competitors about discrimination. As known, the European contract laws are extremely complex, therefore competent legal advice is imperative.
Working design
The double-track tunnels require a break-out profile of 150-160m² with the overburden being generally small to medium. Only the Tunnel Niedernhausen, which passes under the main ridge of the Taunus Hills, has an overburden of 100m. The existing Devonian rock formations of the Rhenish Slate Mountains are deeply weathered and this rock has undergone a later displacement at the surface. The drives therefore require immediate support after excavation.
The working design plans approved by the federal railway authority, Eisenbahn-Bundesamt – EBA, serve as a basis for the assessment of the excavation, and support classes by those responsible on site.
Execution of the working design has been awarded to the contractor, enabling him to respect the working procedures chosen by him in the planning. DB-Guideline No. 853: Railway Tunnel: Design, Constructing and Maintenance, has to be adhered to in the planning.
All the experience gained through construction of more than 200km of railway tunnels during the last 20 years are reflected in this guideline as well as observations of all tunnels operating within the total DB-network9.
For static’s calculations a model has to be chosen for the integrated system, consisting of surrounding rock-mass and support, which reflects real behaviour in nature. The static’s calculations gain more importance for tunnels close to the surface as here critical situations occur without warning, and every tunnel is situated in zones where public safety is concerned10.
The most effective measure for face support in unstable ground conditions has proved to be the use of 8-15m-long face anchors in combination with drilled and grouted steel tube umbrellas. This was used under the Frankfurt-Cologne motorway at the southern end of the Fernthal tunnel. In cases where these measures are not sufficient, the tunnel cross section is divided further (eg side wall drifts, crown drifts).
The sprayed concrete shell is a temporary measure only, so that the steel reinforced inner lining can be placed under well defined conditions. Experience has shown that it is not possible or practical to establish the outer shell in a quality for a durable structure without adversely affecting the mining operation.
Sprayed concrete
More than one million cubic metres of sprayed concrete have been required for the mining operations of the 22 double-track tunnels constructed with shotcrete. A further single-track twin tunnel (Wandersmann Nord) is being constructed, using a shield of 11.5m o.d., whilst seven tunnels are being built by open cut. Best performances have been achieved using the wet-mix sprayed concrete method. Alkali-free accelerators, which can also cope with wet rock conditions, have been developed and tested on site.
In areas where a batch plant could not be kept in constant operation during the night and weekends, dry-mix shotcrete using special accelerated shotcrete mixes and naturally moist aggregates have been applied successfully.
The application of the sprayed concrete is performed regularly by means of semi-automatic hydraulic arms, which allow the operator to control the spraying process by electronic means, thus making sprayed concrete application considerably easier than using previous manual methods11.
Emergency plan
As a consequence of recent tunnel fires, planning for emergencies has gained great importance, and all tunnels have been upgraded to the standard of the EBA-guideline, published in July 1997: ‘Requirements on fire and catastrophe prevention for the construction and operation of railway tunnels’12.
On both sides of the tunnel there are escape routes with a minimum width of 1.2m, which lead to emergency exits, each placed a maximum of 1,000m apart. In this way the tunnels are suitable for both self- rescue and rescue from outside.
The tracks outside the tunnels are accessible for rescue teams at every 1,000m. These are described in rescue plans published to meet the requirements of German standard DIN 14 095.
The rescue teams and the railway personnel have to undergo a training programme before the new railway line is put into operation. These programmes have to be repeated every year so that everyone is prepared for any emergency that may occur.
Geology
The route of the new line Cologne-Rhine/Main in the section north and south runs in Quarternary strata, and in the intermediate section it crosses the low mountain ranges of the Rhenish Massif. The Devonian slates found within this structure have been greatly stressed tectonically.
During the Mesozoic period the rock surface was exposed to a long weathering in a subtropical climate. Volcanic activity in the early Tertiary disturbed the formation even more, and this has consequences for tunnel driving, eg the problem of close proximity of basalt pipes. In historic times, mining and other human intervention has loosened the ground further.
The water table is usually close to the surface.
Tunnel construction
Some of the tunnel structures are particularly interesting, including tunnels with little cover, those in settlement-sensitive areas, and those which, due to their length, have to be qualified as critical in the time schedule13.
The 1,555m-long Fernthal tunnel passes under a closed rubbish dump within its 400m-long middle section. In the course of hydrogeologic investigations slight contamination of the groundwater beneath the dump was discovered.
Prior to starting mining operations in this area, a groundwater cleaning device had to be installed to purify the groundwater until permanent purification is proven. The surface of the dump is being sealed by a combined mineral and plastic cover. The polluted water from the dump is being pumped out thoroughly in advance.
The 2,502m-long Siegaue tunnel, in its 370m-long middle section, passes under a cultural community centre, leads closely past a Romanesque church and passes under a cemetery to the north.
Due to these local conditions the surface is inaccessible and so the tunnel must be built by mining in very adverse ground conditions. These comprise water-bearing loose Quarternary and Tertiary layers of gravel, quicksand, and clay, which connect into the nearby Sieg River. The 220m southern part of the tunnel was mined under protection of a groundwater lowering system consisting of deep bored wells, drilled out of a 3.4m o.d. pilot tunnel, driven by pipe jacking above the planned crown of the main tunnel.
In the last 150m of the northern section the water ingress was so strong that the quicksand and gravel layers became unstable. Therefore a jet-grouted roof was formed from the pilot tunnel with the aim of guarding the crown from water ingress from the over lying gravel. Mining continued after installation of compressed air equipment for pressures of 0.7-1.1bar. In this way, advance rates of 1m per day are being achieved, so that breakthrough can be expected this month (October).
Reinforced inner concrete linings
Reinforced concrete linings form the final structure, and have to meet highest demands in respect of water tightness and durability. The automatic control devices for the signalling alone do not allow wet conditions in the tunnels, all of which are situated below groundwater. This is allowed to be lowered temporarily only during construction, and must recover to its original level after completion. The inner linings are therefore designed for full groundwater pressures.
Water tightness can be achieved at:
Currently no less than 22 steel travelling formwork structures are in operation along the whole route, concreting one block each day. Logistical problems encountered on the supply of material, equipment and qualified personnel are immense, but generally are being satisfactorily solved.
Trackwork
On a length of 192.8km, where the design speed exceeds 200km/h, slab track is being installed instead of conventional ballasted track.
This entails forming a monolithic block whereby the sleeper/rail grid is supported inside a concrete trough and subsequently cast in situ, thus creating a sound rail permanent way known as the Rheda system, named after the town where it was first installed some 30 years ago. Works for this operation started in April this year and have to be completed by the end of September 2001.
Experiences
Mining operations on this project are nearly finished. The motorway BAB A 3 Frankfurt-Cologne has been successfully crossed under 14 times in difficult conditions and without traffic disruption, using mining methods.
Besides this, many additional traffic routes, industrial plants, buildings for supermarkets and leisure centres have been passed under without disturbances to business or residential buildings in Ammerich, Aegidienberg and Ittenbach. All these challenges have been mastered brilliantly.
Hopefully, the experience gained on this project can be implemented on further large-size projects in the near future.
Conclusion
Construction methods in heavy civil engineering have reached an astonishingly high level of development. Today tunnels can be built under preconditions which could not be considered just 20-30 years ago.
This should not lead engineers to believe that natural circumstances can be ignored when choosing the alignment for a new infrastructure project. It is during this early stage that future delays and increases in costs can become, as it were, pre-programmed by the decisions made.
But the main problems with the realisation of new projects today lie, on the one hand, in the area of permission procedures – meaning the persuasion of all those concerned with the project – and, on the other, in keeping costs within the preliminary set budget.
At the beginning of railway construction in Germany the euphoria for this new technology was high. In 1835, the initial public share offer totalled 1.5M thaler (predecessor to the DM) for the first 110km of long-distance railway line from Leipzig to Dresden.
This was oversubscribed in just two days, but it soon became obvious that the actual profits were significantly below expect-ations.
This, coupled with the difficulties encountered during the planning and construction phases, and in the preparatory phase for the operation of other lines, led to a noted fall of enthusiasm to invest in this sector15.
Unfortunately we have learnt little about this matter during the past 135 years.
Related Files
Collection and treatment system
Important projects
Siegaue tunnel
Tunnels on the new NBS Cologne-Rhine/Main route
