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Construction of the A86 motorway tunnel on the outskirts of Paris is expected to restart later this month, after contractors spent four months repairing fire damage to the tunnelling machine.

Around 100m of the concrete tunnel lining was also seriously damaged. It has still to be broken out and replaced following the blaze in March (NCE 14 March).

No-one was killed although tunnel workers had to take refuge in the tunnel boring machine (TBM) for several hours until they could be rescued.

Burning hydraulic oil from a materials delivery locomotive destroyed tunnel fitting equipment and some of the concrete segments of the tunnel lining during the fire.

The 11.24m external diameter TBM which is driving the tunnel was not directly affected by the fire but suffered smoke damage when the tunnel space filled with fumes. Cleaning work and restoration of on board electronics has been part of the work needed to bring the German Herrenknecht machine back to full use.

Tunnel repair work will continue behind the re-started drive. The 100m or so of heavily damaged concrete tunnel lining is being broken out and cut back to sound material before it is replaced.

A similar method was used to repair the Channel Tunnel after its fire in 1996.

Engineers at the joint venture contractor Socatop said the work was helped by the fact that the damaged section of tunnel is in relatively sound limestone and danger from lack of support for the tunnel is minimal. Even the water table is low at this point.

Adrian Greeman in Paris INFOPLUS www. a86ouest. com

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