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CTRL pile tests seek to stabilise marsh crossing

FEARS OVER track stability on section 2 of the Channel Tunnel Rail Link through the west Thames marshlands are behind a major pile testing programme which started last week.

Results from the tests will be used by Rail Link Engineering to provide the basis for a stable foundation design.

A series of static and dynamic tests will be carried out by RLE on 23 huge 600mm square section driven piles, which were manufactured by Aarslef and driven down to 12m by Amey. These tests will be used to assess the suitability of piles to support the CTRL across 7km of the west Thames marshes, ahead of the start of construction, which is expected next year.

In these sections the track passes over between 4m and 10m of very soft marshy ground, overlying alluvial deposits. 'We are dealing with live to dead load ratio of around two, which is high, and very tight tolerances for ride quality, ' Nick O'Riordan, RLE's ground engineering manager told NCE. 'The large piles will resist the high lateral forces imposed by the trains'.

Piling is required in this section because embankments - the favoured solution for high speed rail lines across marshlands in Europe - have been rejected as too visually obtrusive for the CTRL alignment. This means that up to 7,000 driven piles will be required to provide stability for the track.

As well as high lateral forces created during braking, high speed trains are known to produce a 'bow wave' effect in front of a train. This can create bumps in the track, preventing trains from running at high speed.

The tests are expected to be completed by Christmas, and the information will be made available to bidders for contract 310, which includes the west Thames marshes, when the tender is let next year.

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