When T&T International was invited, as the only non-French journal, to view NFM‘s big new ‘baby’, workers were adding the finishing touches, including an unusual back-up crawler undercarriage, to the monster TBM. It was then to be disassembled for transport by land and sea to the Netherlands (News February and September ’00).
The project
The Groene Hart tunnel is part of the international ‘Thalys’ high-speed train link being constructed between Amsterdam, Rotterdam and on to Antwerp in Belgium. Its inclusion in the Amsterdam-Rotterdam section which includes viaducts, cut-and-cover tunnels and track at grade, is environmental. Country areas are now rare in the western part of the Netherlands, and the HSL route cuts straight through the largest chunk, the Randstad. The area has special conservation interest, with rare bird species.
The environment is also the main reason for adopting a twin-track design for the tunnelled route as opposed to the two 9.3 diameter bores of the original design. Excavation of a single large tube produces less material for disposal and, in the process, requires the world’s largest TBM at 14.87m od. It is also set to save a reported FFr500M ($69.8M) on the cost of construction.
The single bore eliminates the need for excavated cross-passages which would have required time consuming and expensive ground-freezing. Instead the single tube is partitioned with reinforced concrete slabs which have escape doors for passengers in the event of a fire or other incident. The design also allows construction of more frequent escape passages – recent fire incidents have shown that 300m is too great a spacing between cross-passages. Three emergency escape shafts, down to 43m depth, are positioned 2km apart, each incorporating “technical rooms” for transformers, pumps, switchgear and similar equipment.
The tunnel construction also includes a technical gallery to carry cables for the trains’ catenary supply. Ramps at each end of the main tunnel will be constructed in cut-and-cover.
The TBM system
Bouygues selected the NFM design from a “wide variety” of TBM options, costing the joint venture FFr200M ($27.9M).
NFM, 50% of whose income comes from TBM design and construction, has previously built TBMs for Bouygues for projects in Milan and China. Manufacture of the Groene Hart TBM at its Creusot works in Burgundy has presented considerable logistical challenges. The cavernous assembly hall, part of the 80-year-old works, is one of the few in Europe suitable for such a task. The cutterhead alone holds a claimed world size record for machined parts, for which the work’s large oven is used to ease post welding stresses; another feature claimed to be unique. The shortness of time taken for designing and constructing the machine is another record claim, but with such an unusual development, comparisons are difficult.
Many casual observers are concerned by the 3,520t total weight of the TBM (1,800t for the cutterhead), and predict that it will sink in the soft ground. While admitting potential stability problems, which have been overcome, NFM and Bouygues say that extra weight of 500t was added to prevent flotation from ground pressures at depths of as much as 45m. The natural level of water in the area is 4m above the ground level but is, of course, lowered by the Dutch national drainage system. The water also contains marine salts which have to be compensated for by additives in the pressurised slurry lines. Salt water drainage must not mix with fresh water in the rivers and must be treated before re-use or discharge.
When asked about procedures for cutter changing, bearing in mind the difficulties experienced on the Westerschelde project, Bouygues engineers were dismissive of the need for special measures. Cutter wear is not expected to be significant in the soft, sandy ground anticipated. NFM engineers, however, say that pressures of 3-3.5bar will have to be counterbalanced at the face for any cutter changing, and that two teams of divers are being allocated to the project. It should be possible to change peripheral cutters within the air bubble, which is part of the TBM’s operating system.
But the distinctive element of the TBM promoted by NFM is the extensive monitoring systems, producing data in 2000 parameters in “real time” for automatic or manual control functions. Monitoring routes also run by fibre-optic cables to the surface control centre. All noise-producing equipment, such as compressors and power packs, are housed in acoustic enclosures.
The lining for Groene Hart, erected within the TBM shield, comprised of a 10-piece, 2m-wide precast concrete segment ring. Bouygues Groene Hart project operations director Joseph Henois told T&TI that the client had accepted Bouygues’ own design for the lining, although TU Delft had been testing a smaller series of segment rings as used for the Botlek tunnel. Data from these tests, primarily on the performance of the joint interfaces and bolted connections, were made available from the Dutch ministry of transport.
The TBM is due to be shipped this month to arrive on site during June, and construction is scheduled for completion during summer 2004. Handover for operation is expected the following summer.
The contractor
Bouygues is the major, 90% partner in the Groene Hart contracting joint venture with Koop Holdings. The only other final bidder was a joint venture of Hochtief, GTM and Campenon Bernard.
As the world’s largest construction contractor, with 40,000 salaried employees, Bouygues is setting about raising its international profile with particular emphasis on “grand” projects with strong
“value added”. Recent tunnelling contracts have included the Sydney Metro, the Kwai Tsing tunnel on Hong Kong’s West Rail project, the Murgenthal in Switzerland, the Cairo Metro and the Channel Tunnel.
Currently 75% of work is already outside France, but Michel Cote, Bouygues Travaux Publics’ managing director said, “We want to be considered as a global contractor”. The company is aiming at 70% of its growth to be outside France by 2005 and its financial size will be a major advantage in a competitive market.
Jean-Pierre Combot, president of the Bouygues Construction parent company, reported that the company had FFr41.5bn ($5.8M) worth of work on order during 2000, compared to FFr40bn the previous year. Strong progress was aided by the ‘dollar effect’, he said, as well as “good market orientation”.
Related Files
The Groene Hart tunnel forms part of the Nord-Zuid HSL line
Cross-section through the Groene Hart tunnel
