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Etched across the landscape

France High speed rail

France is into its third decade of high speed railway construction. Andrew Bolton reports on the new Ligne a Grande Vitesse between Paris and Strasbourg.

Out in the fields of eastern France, slivers of chalk embankment have begun to appear across the seemingly endless farmland. These and the occasional roar of an earthmoving truck are the first signs that work on SNCF's 300km high speed Ligne a Grande Vitesse (LGV) railway between Paris and Strasbourg is gathering pace.

Work on a 45km section north of Chalons-en-Champagne began in earnest last year, with Belgian project manager Tractebel overseeing the work of French contractor Roger Martin.

Chalk exposed by the work now marks the trace of the line over long stretches of the flat countryside east of Reims.

On Tractebel's section of the route, embankments and cuttings have started to take shape and contractors are building the first of 45 viaducts which will carry the route over or under motorways, local roads local railway lines and farm tracks.

'We have a bridge almost every kilometre, ' says Tractebel structures manager Dominique Friot. 'They will re-establish all the routes which have been cut by the line'.

The 300km route includes 327 structures ranging from a 1,100m crossing of the Moselle flood plain to those taking farm tracks across the line.

St Hilaire du Temple, a sleepy village north of Chalons, is soon to be transformed into one of the project's main hubs. A railhead now under construction close to the village will supply materials to sites to the east and west and will feed tracklaying work when it begins next year.

The village is on one of two neighbouring sections of the route being project managed by Tractebel and built by contractor Roger Martin. At St Hilaire the contractor has already completed earthworks for the railhead and for a temporary village to house 200 track workers.

Work on Tractebel's section been fairly straightforward, as this part of the line cuts across relatively flat farmland, which requires only the excavation of shallow cuttings and low level embankments.

The porous chalk that lies along most of this section presents a more difficult challenge however, because in wet conditions reworked chalk fill becomes soft and malleable and prone to settlement.

To prevent this, the chalk has been excavated, broken and then mixed with 3% to 5% cement during dry weather. On embankments, treatment is applied to a 5m base layer and then to each 350mm layer as they are built up.

The resulting chemical reaction creates heat, which evaporates water and leaves a more stable material on which to build the line.

Two major viaducts are part of this section, where the line crosses the A4 Paris-Strasbourg motorway and local railway lines.

Both are 100m long composite structures, supported on abutments in embankments running next to the motorway and a pier located in the central reservation.

The motorway crossing spans are especially long because the high speed line crosses at a particularly acute angle, and there are plans for future addition of extra lanes to the two lane dual carriageway.

Both viaduct decks will be prefabricated on the approach embankments and jacked across the motorway over a period of two days.

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