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Working with piles


As the CTRL tunnels crunch into the ground at Ripple Lane one of the first things they meet 10m below the surface will be the piled foundations of a building in the Freightliner Terminal.

Fortunately the building is redundant, which means it can be demolished. Unfortunately there is not much in the way of structural records.

So Team 250's first task is to find out what the piles are made of. The TBMs would be able to deal with unreinforced piles, but they are not designed to cut through reinforced concrete and this risk has to be removed.

The plan is to trepan the soil out from around the piles using a toothed casing, and attempt to extract them from the surface before tunnelling starts.

Whatever the final solution, it is a classic example of CTRL's collaborative approach to problem solving. 'The joint venture will get paid the actual cost of the work plus a fee, ' emphasises RLE contract manager Phil Hockley. The result is that a difficult physical obstruction to construction will not develop into a contractual battle.

Later on the tunnels will meet an even more difficult piling problem when they pass under the A13 railway bridge at Alfred's Way. The bridge was built in the1970s and construction records are limited but eight piles are expected to obstruct the tunnel line.

Whether reinforced or not, the piles are vital supports to a prime and heavily used highway. There is no question of simply tunnelling through them. Instead, plans are being formulated for a delicate operation to tunnel around the piles and transfer their loads to new foundations burrowed out above the line of the CTRL running tunnels.

The general concept is to hand dig a shaft beside the bridge abutment and drive a pair of 2m diameter tunnels either side of the existing foundations. Cross tubes will then be excavated to intersect the piles and create new pad footings. Once the loads are transferred further adits will be opened up at a lower level to intersect with the pile bases so these can be demolished before the TBMs arrive.

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