The A86 West-Eastern tunnel is being built to alleviate traffic congestion and improve traffic links between Parisian suburbs. The completion of an outer ring road will greatly relieve pressure on the existing road infrastructure and guarantee moving traffic. The A86, when finally completed in 2010, will allow the journey from Malmaison to Versailles to take only ten minutes, rather than 45. The A86 West tunnel will be formed of two toll tunnels at a cost of 2.23bn euros; one will be an innovative 10km double-deck tunnel (duplex motorway) for light vehicles, the other at 7.5km, with just a single deck designed for all vehicles including HGVs. The proposed route for the A86 includes a stretch through the west of Paris, a problem area where road building is concerned. A mainly residential area, Versailles features some important historical monuments and protected woodland areas. After rejecting 22 proposals, the A86 West underground solution was accepted as viable.
Tunnel boring for the first section was completed in October 2003. Fittings of the tunnel and remodelling the A13 toll plaza started in April 2004. Digging was started for the second section of the tunnel in June 2005 and completed in August 2007; a fitting out of the dual deck tunnel was started with an opening scheduled for 2010. The final part of the TBM operation concerned the installation of arch segments to provide the structural finish to each tunnel, seven of which comprise to make a ring together with one keystone. The segments were fabricated from prefabricated reinforced concrete and weighed 11t each. A joint was fitted over the whole circumference to guarantee water tightness.
The tunnels were constructed using an all-terrain, made-to-measure TBM, fabricated and supplied by Herrenknecht AG, Germany. The TBM used had three operating functions, being able to simultaneously drill underground, remove excavated materials and perform progressive structural finishing through arch segments. As the TBM was adaptable, it could be changed in diameter to meet the different bore requirements of each tunnel. The TBM could be configured to operate through different geological layers with a Mixshield, ranging from hard layers such as limestone to soft layers comprising water and clay. In addition, it followed a precise boring course utilising a laser guiding system, progressing at an average daily rate of 30m.
This construction technique provides an extremely strong and rigid structure that can easily handle the stresses placed upon it. The tunnel tube consists of a series of vertical slabs fixed to corbels embedded in the tube lining walls; these form the structure to support the road and are made from reinforced concrete. Ventilation systems (31 in this 4.5km section) have been installed above and below traffic lanes, which will ensure that there is a permanently renewed atmosphere in the tunnel with highly efficient smoke extraction in case of fire. In the East tunnel, these will be split by a vertical partition to provide extraction on one side and fresh air ventilation on the other. With just one level of traffic, the West Tunnel will have an extraction system in the top of the tunnel and a fresh air ventilation system at the bottom. The west tunnel has 31 emergency refuge areas (ERAs), 13 of which are also smoke evacuation ERAs. Furthermore, there are 18 interconnecting stairways for emergency use in the tunnel. Emergency systems also include four emergency shafts including Hauts Bénards and Bois de l'Etat emergency shafts in Rueil Malmaison and Place Berthet and Le Butard emergency shafts in La Celle Saint Cloud. Both tunnels will also use HI-FOG fire protection technology, which is a high pressure sprinkler system that produces a fine mist of water (droplets 50–120µm) to damp down smoke or extinguish and cool fires. The system only uses non toxic water, which was developed and marketed by the Marioff Corporation. The East tunnel will have 13 ERAs with smoke evacuation vents and interconnecting stairways. There will also be five emergency shafts: Prieuré in Marnes la Coquette, Carrousel in Versailles, Viroflay railway station in Viroflay and Porchefontaine in Versailles (here there will also be an ERA). The French State granted concession to Cofiroute for A86 construction. Cofiroute appointed Socatop, an association that brings together three of the biggest construction and road industry companies in France, VINCI, Eiffage Construction and Colas, as consultant engineers and contractors, as their remit includes construction work. SENDIN provided reinforcing steel and Formwork has been provided by several companies, including Bernold-Ceresola AG, PERI S.A.S. France, RB-PIM and Simpra. Bonnard & Gardel provided consultant engineering services for the project (geotechnics and hydraulics) and multi-service vehicles were provided by TECHNIMETAL.
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