AARSLEFF PILING, the UK subsidiary of Danish contractor Per Aarsleff, has made what are believed to be the largest square section continuously reinforced precast concrete piles in Western Europe.
The 600mm by 600mm piles have been cast in 5m,7m, and 8m long sections at the firm's factory in Newark, Nottinghamshire.
Aarsleffwill install the piles as part of an extensive pile testing programme being carried out at the point where the second section of the Channel Tunnel Rail Link crosses the West Thames marshes area at Havering and Thurrock, Essex.
Aarsleff is working in joint venture with contractor AMEC for Union Railways (North), the firm responsible for building phase two of the high-speed rail link.
The 23 test piles, designed by CTRL project manager and designer Rail Link Engineering, will be installed by one ofAarsleff's Banut 700 hydraulic piling rigs through soft marshy ground and founding on underlying gravel beds in two areas.
The rig will drive 13 of the 8m long piles in one location and 10, 12m long piles in the other. Each of the longer piles will be made up of 5m and 7m sections, rigidly joined with Stabalator joints.
The test piles are being fitted with strain gauges for vertical load tests and inclinometers for lateral load tests. Some of the piles have been cast with internal steel and PVC tubes so that strain gauges, accelerometers and inclinometers can be installed to monitor the piles during the testing programme.
This will include a dynamic test straight after driving which will be repeated one week later. The piles have been designed to accommodate a combination of compressive and lateral loads applied cyclically. RLE will test and monitor pile behaviour in the soft ground and the results will be used to determine the final foundation design for the high-speed rail line.
The piles have been cast in special moulds using a new self-compacting concrete mix recently introduced in the manufacture of the firm's smaller and standard square section continuously reinforced precast concrete piles.
The large section test piles for CTRL are heavily reinforced with eight longitudinal T20 bars and 10mm links. Self-compacting C50 concrete is taken from the batching plant to the casting area by a 1. 5m3 skip running on a monorail and transferred to a delivery hopper for discharge directly into the moulds.
The special high slump, fluid concrete, which Aarsleff has developed in partnership with RMC, flows into the moulds and around the reinforcing without the need to use poker vibrators. Piles are struck 16 to 18 hours after casting and allowed to cure for two weeks before driving.
The CTRL will link the Channel Tunnel with St Pancras station in north London. The 74km long section one through Kent is 45% complete and preliminary works on section two, the 39km stretch between north Kent and central London via new stations at Ebbsfleet and Stratford, have begun. Main construction is due to start in mid-2001.