les palonniers du métro par Acimex e1443186378767Officially opened in 2002 with just one line, 9.4 km long and encompassing 15 stations, the Rennes underground will be getting a second line, line B, in 2017.

Digging is currently under way at a speed of 10 cm per minute. At a depth of 25 metres, a north-east/south-west line (8 km long, encompassing 14 stations) is in the pipeline. ACIMEX has been committed to the project, as it supplied vacuum lifters for handling concrete segments. Concrete segments set up the tunnel structure after being assembled into a ring once the TBM has digged.

The segments are prepared in moulds in the same way as cakes, placed in the curing room at 40° and then taken out of the mould before being dried and stored. ACIMEX has supplied the vacuum suction pad handling equipment for taking the segments out of the moulds via the extrados side. The demoulding vacuum lifter has a load capacity of 8 tonnes. The segment is turned over and picked up again on the intrados side. ACIMEX equipment has a load capacity of 8 tonnes. Self-contained machinery (supplied by ACIMEX) takes the stack of segments to the storage area until the segments are completely dry. When ready, the segments will be taken to the head of the tunnel boring machine to be put in position.

In absolute terms, the tunnel boring machine would take four months to dig the 8 km long tunnel, but in reality the work is scheduled to last two years or more. The tunnel boring machine is progressing at snail’s pace. It is 82 metres long and weighs 1450 tons. It digs and digests the earth dug out (600,000 m3 overall) and then stops to build. The construction: concrete components called segments that are arranged in a ring. These will give the tunnel the structure that the boring machine will use for support as it progresses.

The segments were manufactured at the Bonna Sabla plant in Bruz, just like the segments used in the first underground line. The plant was built and delivered ready for use by CBE Group, which specialises in the design and delivery of segment precast plants.

ACIMEX, the expert in heavy handling, can work with you on your projects. Please contact us or ask us for a quote.

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