North Downs Tunnel
Today, the section of line sandwiched in-between the Medway Viaduct and the northern portal of the North Downs Tunnel is a non-descript site. It is bordered on one side by the M2 Motorway, and on the other by Nashenden Farm. However, during 1993, when potential sites for international stations were under review, the land at Nashenden became significant, if only briefly. The site was one of four considered for the placement of an intermediate park-and-ride international station facility; Ebbsfleet, Rainham (Essex), and Stratford were also in the frame. By October 1994, Ebbsfleet had been confirmed as the proposed site for the station, and Stratford only remained as a possibility, if a strong financial case could be made for it. The very fact that Nashenden was an isolated site, with no industry or local population in existence to support the CTRL scheme, sealed its fate. Although no station would be provided here, two interesting engineering feats would still reside in the immediate vicinity: the Medway Viaduct and the North Downs Tunnel.
On 13th October 1998, two major engineering contracts were awarded to consortium ''Eurolink JV'': those of the Medway Viaduct and North Downs Tunnel. Eurolink JV comprised three corporations:
Beton und Monierbau GmbH: An Austrian firm which specialises in tunnelling and building underground infrastructure (GMBH: Gesellschaft mit Beschränkter Haftung. This is the German translation of a limited liability company).
Morgan EST: A UK-based civil engineering firm specialising in numerous industry sectors: road and rail, in addition to electricity, gas, and water. This company was also later involved in the Thurrock Viaduct construction programme (EST: Early Solutions Together).
Vinci Construction Grands Projets: A French civil engineering firm which also later became part of the team constructing Thurrock Viaduct.
Beginning of construction work onsite was announced on 15th October 1998. The proposed location of the North Downs Tunnel, under Bluebell Hill, presented a couple of obstacles: firstly, the land which it would pass beneath was environmentally protected. This prevented the installation of pressure shafts, which meant that the tunnel diameter would need to be wider than usual to compensate for this. Secondly, it was initially unknown how solid the surrounding chalk was; this would determine how much reinforcement the tunnel walls would need. A two-mile long bore was required through the Kentish chalk, with a diameter spanning 42 feet. The boring operation was deemed complete on 8th June 2000, and on the 19th of the following month, lining the insides of the tunnel with concrete began. The excavated chalk was of greater solidity than initially thought, thus this had a positive bearing on timescale and costs. Consequently, the extent of the tunnel's wall reinforcement could be reduced, permitting thinner concrete layers. Tunnel construction work came to a conclusion on 7th August 2001, the hard chalk terrain ensuring that the quoted £75 million contract was completed two months ahead of the given deadline, with a total cost saving of over £5 million.
7th August 2007
The double-track CTRL line is seen plunging into the northern portal of the two-mile long North Downs Tunnel on 7th August 2007. In the foreground is the London-bound carriageway of the M2, which was upgraded to four lanes each way at the time of the adjacent railway works. © David Glasspool
7th August 2007
A view towards the tunnel portal on 7th August 2007 reveals the Nashenden site once outlined as the location for an international station. On the left of the line is the M2, whilst to the right of the tracks is Nashenden Farm. © David Glasspool
7th August 2007
A north westerly view on 7th August 2007 shows the line descending towards the Medway Viaduct. There are two crossovers here, situated no more than 160 yards apart. The first can just be seen, this being a ''facing'' crossover, whilst the ''trailing'' crossover is beyond it. © David Glasspool
Here is a feature which even a regular user of the line would not know exists. Approximately 10-metres inside the tunnel from the London-end portal sits a statue of "St. Barbara", patron saint of tunnellers and miners. At window level you can see where the cable troughs are routed around the cutout in the wall on the "down" side. © Paul Cooper-Hayden
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