Boring is scheduled to re-start in the middle of this month on the 10km long A86 road tunnel near Paris following the major fire on March 3rd that halted production and lead to the evacuation of 19 workers from the tunnel.
As T&TI went to press investigations were still underway to confirm the cause of the fire that started 1.5km from the tunnel entrance at Rueil-Malmaisonin and 400m behind the 11.6m diameter Herrenknecht EPBM constructing the tunnel. The fire is known to have started in the leading loco of the train supplying the TBM with precast segments and mortar needed to build the 8 element rings. The train was passing under the bottom slab of the future double deck tunnel and was right underneath the shuttering prepared for the next section of the slab.
As French fire fighters fought to control the blaze, the 19 tunnel workers sheltered in the TBM using the emergency air supply until they were rescued some four hours later and taken back down the tunnel via the median slab. There were no fatalities, one fireman was seriously affected by smoke inhalation although he had fully recovered the following day.
The fire has highlighted the importance of adequate safety precautions during tunnel construction. The emergency procedures at the A86 have received high praise and been credited for preventing the accident turning to tragedy. From as early as the design stage of the TBM, Socatop launched a special working team to optimise safety and fire fighting devices and initiatives. These included a water curtain at the rear of the TBM to reduce smoke ingress, a spare water tank on the TBM, the use of fire resistant hydraulic oil and a 10-hour air supply to the air locks.
Regular drills had been carried out based on various scenarios that included a fire breaking out under the slab, over the slab, between the end slab and the TBM and on the TBM itself. Mr A. Verdier, project manager of design and build JV Socatop, told T&TI, "Several safety exercises were organised in situ with Socatop personnel and firemen, this training greatly helped our TBM team to react with calm and in total compliance with safety procedures."
Initial inspections of the damaged area show the damage to be limited, Verdier confirmed, "Roughly 150m of the tunnel vault has been affected by the fire. There’s been maximum spalling depth of about 5-6cm on the 42cm thick segments, all the lining remains and there is no rock exposed."
A costing exercise is currently underway although the contractor is insured for fire damages.
