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Contractors World 2010 Volume 1 Issue 10
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 PANORAMA

Sections passing over soft ground and flood plains require support on a grid of driven displacement concrete piles. About 1,500 precast concrete piles support these sections of the embankment and transfer the load to the underlying sands and gravels. England
Piling as part of congestion relief of major town

Authorities in the county of Kent, UK are building a new section of road on the northeastern outskirts of Sittingbourne to ease congestion in the town centre and considerably improve access to the an existing Eurolink Business Park.

Consulting engineer, Jacobs, designed the scheme and is also supervising the construction. The $20 million civil works contract went to Jackson Civil Engineering.

The new 1.4 km single carriageway - the Sittingbourne Northern Relief Road - includes a three span steel and concrete composite bridge over a tidal creek and on to an embankment. It also crosses a disused landfill site to another shorter, but similar, composite steel and concrete bridge with a single span of 41 m over a narrow gauge light railway. The project also requires an embankment to cross the low-lying Kemsley Marsh flood plain.

Sections passing over soft ground and flood plains require support on a grid of driven displacement concrete piles. About 1,500 precast concrete piles support these sections of the embankment and transfer the load to the underlying sands and gravels.

Jackson, which started on its two-year contract towards the end of 2009, awarded Aarsleff Piling an approximate over $1 million contract to supply and install the 350 mm square section piles. The piling contract also included some trial piling and static and dynamic load testing to confirm and corroborate Jacobs’ design.

The testing revealed that some longer piles up to 17.5 m were needed across part of the landfill area to achieve the required 800 kN compressive working load. These longer than originally anticipated piles incorporate mechanical joints and are made up of under piles with pin jointed over piles to the required length at each location.

These were supplied by Aarsleff’s subsidiary, Centrum Pile, which supplied all the contract’s precast concrete piles Centrum Pile is probably the only pile manufacturer in the UK able to produce precast concrete piles over 15 m long with mechanical joints to the highest Class A, in compliance with the harmonised European Standard, BS EN12794:2005 Precast concrete products (Foundation piles).

Aarsleff used two of its own piling rigs on the project with the smaller Banut 700, equipped with a free fall drop weight, working on part of the northern section of the embankment.      Aarsleff used two of its own piling rigs on the project with the smaller Banut 700, equipped with a free fall drop weight, working on part of the northern section of the embankment.

It had to drive about 240 of the shorter piles, all 11.5 m long and predominantly in rows of 23 on an approximate 2 m grid. The company’s largest Junttan PM26 LC worked on the southern section installing around 1,250 of the longer piles up to 17.5 m.

These are in rows of seven and on a larger 3 m grid pattern. The PM26LC, with accelerated impact hammer, has an adjustable stroke of up to 1.2 m. It is operated from the rig’s hydraulic system and hydraulically accelerates the drop weight during the fall, boosting the impact energy and increasing by up to 20% the efficiency at full stroke over a conventional free fall drop hammer of the same weight.

The hammer with its heaviest 9 t weight produces maximum impact energy of 106 kNm at full stroke. Impact energy, stroke and blow rate can be infinitely adjusted by the rig operator to suit ground conditions and pile type, as the accelerated hammer is suitable for driving all types of precast concrete, steel tube, sheet and timber piles.

“Aarsleff’s 21 week duration piling contract has gone very well and they finished about two weeks ahead of programme,” says Jackson contracts manager Andy Nailor. On completion of Aarsleff’s piling contract, Jackson followed on trimming the piles to length and tying them into individual 900 mm and 600 mm square, 300 mm deep cast insitu pile caps. These will then be overlaid and linked with a bidirectional geotextile blanket to accommodate the initial load platform, prior to building up and completing the embankments in a series of layers to road level.

Aarsleff
Banut
Junttan

 

 

 

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