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Massive piling contract gets under way on CTRL

UK FOUNDATION contractor Aarsleff Piling has begun its largest ever contract - the £4.25M supply and installation of 600mm square section precast concrete piles on Contract 310 of the Channel Tunnel Rail Link.

The 18-month contract follows earlier test pile work, when Aarsleff installed similar piles at two sites in Rainham and Purfleet, Essex (GE March 2000).

Testing, monitoring and analysis of pile behaviour during and after driving in the soft ground was carried out by Rail Link Engineering, and the data used to produce final foundation design and pile configuration for Contract 310 which began last month.

Working for joint venture main contractor Morgan-Vinci, Aarsleff will install about 3000, 9.5m to 18m long piles, typically in rows of four and six at 5m centres.

The piles will support sections of the 7km long, 10m wide reinforced concrete track slab that will carry the high-speed line over soft ground on the West Thames marshes at Havering and Thurrock.

Ground conditions are mostly 4m to 10m of alluvium over flood plain deposits, tertiary clays and sands or chalk.

Aarsleff's fleet will be bolstered by equipment from Danish parent group Per Aarsleff, including a Hitachi self-erecting rig, modified to handle the large piles.

Casting of the continuously reinforced concrete piles began at the firm's factory at Newark, Nottinghamshire in June.

They are being cast using Aarsleff's free-flowing, self-compacting concrete mix. The mix, which does not need any vibration and flows like thin custard into the moulds and around the rebar, has been used for more than two years to manufacture smaller and standard square section piles.

The CTRL piles are being cast in maximum 14.2m long segments weighing 12.5t. Rigid mechanical joints will be cast into the ends of some piles to achieve the maximum 18m required on site. The piles usually reach a strength of 24-28N/mm 2at 21 hours. The moulds are then stripped.

The CTRL piles also incorporate full length chamfered corners and a domed head, which means the normal reinforcement bands needed for driving conventional flat-topped piles can be dispensed with.

The £178M, 11.4km long Contract 310 runs between the tunnel portals at Ripple Lane and the tunnel approaches at West Thurrock Marshes. The section includes the 520m long Rainham Viaduct, the 1km Aveley Viaduct and the 1.2km Thurrock Viaduct passing over the Dartford Tunnel approaches and under the Queen Elizabeth II Bridge.

lAarsleff Piling and Stent Foundations have merged their concrete pile manufacturing operations in England and Wales to form Centrum Pile.

The 50/50 jointly owned firm is based in Newark, Nottinghamshire. It will use its expanded capacity to 'substantially' increase production of precast piles. It will supply them at 'competitive prices' to Aarsleff and Stent, which will continue to individually supply piles to foundation companies in the UK.

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