At 10.00 am on Saturday 9th June, after following Robert Broach’s excellent instructions some 27 ICE, IET, IMechE, IStructE and CNISF members and partners met at the site offices of EGIS Rail at Vélizy.

These site offices are located at the entrance portal to the 1.6 km tunnel section of the new 14 km tram line currently being built between Chatillon Montrouge and Viroflay - Rive Droite. Lucy Rew, Chairman of the ICE French LA, who is the site Works Director for Egis, the engineers responsible for the project, met us there and gave us a very interesting overview of the structure, funding, design and execution of the tunnel project.

There are five parties funding this project, the Île-de-France Région, the state, the Yvelines Département, the Hauts-de-Seine Département and RATP the eventual operator of this line. The total cost of the civil works is €384 million, of which the tunnel section accounts for €82 million and in addition €134 million will be spent on the tram rolling stock. The two Départements and RATP are the clients for the works, which means that Egis need a diplomatic approach to problem solving and decision making!

The tunnel section runs through two underground stations (Viroflay-Rive Gauche and Viroflay-Rive Droite) and a combined ventilation and emergency shaft. We visited all these sites during our site tour in the afternoon.

The entrance portal for the 9 m diameter TBM (tunnel boring machine) is located in an area of forest but then runs at 20 metre depth on average under the built up areas of Viroflay. The soil profile is mixed sands and marls with three separate water tables and the tunnel, which the TBM will bore in 2013, runs generally at or above water table with one deeper section where the line passes under a large diameter main sewer. The critical path for construction runs through the underground stations, which are being built in very congested and restricted sites adjacent to existing SNCF and RER stations. 

The station construction is top-down and the diaphragm walling is in progress at Viroflay-Rive Gauche in a complicated two stage process which requires considerable traffic management. The road through the site is restricted to a single lane for cars only in a very tight chicane, which has already caused problems due to large trucks ignoring the signs, Lucy informed us. Pedestrians are also inconvenienced but thanks to an extensive information policy for local inhabitants there are remarkably few complaints, showing that the provision of this tram service is generally welcomed. Environmental issues have revolved around the clearing of forest areas, but 9,500 saplings will be replanted when the working areas are cleared at the end of the project. 

Delays by utilities to service diversion works on the line of the drive are already putting strain on the overall programme of 43.5 months, starting from December 2011. Station possessions and restricted train speeds are necessary when the TBM runs under the existing rail lines and the dates for these have had to be agreed with SNCF two years in advance to meet SNCF’s timetable planning constraints. Delays due to service diversions will restrict the TBM’s progress and further delay could mean that the TBM will miss the agreed timeslots for the drive under the station areas.

The diaphragm walls for the ventilation shaft have been installed but the shaft will not be excavated until the TBM has driven through the base of the shaft. Fibre glass reinforcement has been used in these walls in the area of the tunnel drive to enable the TBM to cut through and continue driving. This saves time (the TBM does not need to be jacked through the empty shaft) and reduces the problems of waterproofing at the interface between shaft and tunnel.

The Herrenknecht TBM that the contractor Eiffage will use for the drive next year has already been in use on the Metro 12 line in Paris. The 82 meter TBM train is now lying at the tunnel portal area like a giant meccano kit waiting to be reassembled for the start of the drive early next year – “toys for boys” as Lucy said, but very interesting for us visitors to work out what goes where!

Thanks were also expressed to Robert Broatch for his organisation of the day’s events and to those in the party who came to site by car and generously ferried the others around the narrow streets of Viroflay during the visit.

Derek Gear CEng MICE, Secretary of French Local Association and ICE Member in France