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TECHNOLOGY MANAGEMENT |
During the 1970s, SNCF and BR had developed the "mousehole" project - rail only with one 6m running tunnel. This was rejected by the British Parliament in 1981 on the grounds that it did not provide for vehicles, and that its sponsorship by the two nationalised railway systems meant that it would not be able to raise the finance required. A UK/French Study Group commissioned by the two governments reported in early 1982 that a twin bored rail tunnel capable of carrying vehicle shuttles was the most appropriate solution. Bridges, immersed tubes, artificial islands, and ventilation shafts were all seen as having unpredictable consequences on the hydrology of the Channel and posing a threat to shipping. Moreover, a drive across route posed a threat to the continuance of the ferries which would still be required to carry dangerous loads and to provide competition for the new facility (Hunt 1994 p 164). A Franco/British Channel Link Financing Group, mounted at the initiative of the banks reported in May 1984 that the only option that offered commercial viability was the CTG's proposal, but with a six year construction period it offered no chance of being financially viable without government guarantees. A reanalysis of the project by the CTG established that the programme could be reduced to 4.5 years with a 10% increase in construction costs (Hunt p 167). This reduction was critical in establishing the feasibility of the project. On this basis, the invitation to tender was prepared by an Anglo/French Working Party The invitation to tender in 1985 received four responses, two of which can be considered to have been serious - the successful one and Euroroute which was a drive-through bridge/tunnel combination promoted by, amongst others, GTM and Usinor on the French side, and Trafalgar House and British Steel on the British. The concept involved two bridges leading to artificial islands which were then connected by a 25km tunnel. The CTG/FM proposal was accepted on the grounds that it:
The proposal consisted of twin 7.6m running bores capable of carrying shuttle vehicles with a 4.8m service tunnel running between them with a vehicular facility provided by a "rolling road" shuttle service. Technically, it was virtually identical to the 1973 attempt, except that the running bores had been enlarged; indeed the concept had been fully developed in 1960 by the Channel Tunnel Study Group (Lemoine 1994 p 93).
The details of the enormous engineering and logistical effort can be found in (Harris et al 1996; Kirkland1996; and Penny 1996). While the overall principles of engineering design were necessarily the same on both sides, different engineering choices were made according to differences in practices between the two sides, and differences in the geological conditions. An example of this is the differences in the tunnelliers. 11 tunnelliers (tunnel boring machines) were required to bore the three 50km tunnels, as shown in table 1. The French-based machines were of the more sophisticated and expensive closed face (c/f) type rather than open face (o/f) due to the more difficult ground on the French side, particularly a fault just off the French coast. The original intention of procuring these tunelliers within France was frustrated when France's sole manufacturer went into liquidation (Financial Times 6/4/88). Due to the much shorter length of the French landward drives, only one machine was required to bore both main tunnels. Another example is the choice of the innovative New Austrian Tunnelling Method (NATM) for the construction of the two British cross-overs where TML drew heavily on the expertise of the Austrian firm of Ingenieurgemeinschaft Lasser-Feizlemayer. This technique, while cheaper, poses greater risks, and was rejected by the French engineering team who chose a more traditional method because of the greater uncertainties regarding the geology on the French side. A third example is in the engineering of the over-bridges for loading at the two terminals. As TML's Chief Executive explained,
The terminal works were not especially challenging, although the constrained size of the UK terminal at Cheriton meant that extensive land stabilisation was required. The mechanical and electrical services, however, posed a variety of challenges. The catenary systems within the concession area are built to TGV specification, although achieving this in the context of the tunnels meant considerable innovation. The track beds, destined to become the most intensively used in the world, use an American ballast-free system. The tunnels are artificially cooled and ventilated, although the ram action of the trains provides significant ventilation as well. The shuttle trains themselves pose few technical problems, although the overall system may be described as one of the most sophisticated transport systems in the world. The Eurostar trains which take the through train services through the tunnel have to cope with the systems of France, Belgium, and BR's erstwhile Southern Region. The French TGVs normally have synchronous motors, but it was decided to use instead GEC's new asynchronous motor on the grounds that its lighter weight allowed the installation of the equipment necessary to cope with the three different railway systems. The main environmental problem posed by this project - as opposed to the associated high speed rail link projects - was the disposal of the 8m m3 of spoil from the tunnels. Although there had been considerable opposition to the use of the Cheriton site as a terminal in the early 1970s, this was no longer a major issue. The 5m m3 spoil from the UK side was used to reclaim land from the sea at the foot of Shakespeare Cliff, while the French tipped their 3m m3 behind a dam in a dry valley at Fond Pignon.
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