Precast Concrete
St Mary’s Island, Chatham Maritime
Aarsleff Piling supplied and installed nearly 6000 precast concrete piles through soft ground at St Mary’s Island, Chatham Maritime in north Kent for what is believed to be one of the largest residential developments in the southeast of England. The fully reinforced piles, between 16m and 26m long, were ideally suited to the adverse ground conditions and provided foundation support for flats, two and three storey town houses and detached homes on the vast flood protected site on the River Medway.
House builder Countryside Maritime Ltd, a joint venture between Countryside Properties and the South East England Development Agency, designed and built about 1200 of the approximate 1700 properties on the former Brownfield site. The joint venture company, through its housing contractor, Countryside Properties, developed the vast majority of the St Mary’s Island site, which, with its great basins, was built on former wet marshland by convicts between 1862 and 1875. St Mary’s Island formed part of the Royal Navy’s Chatham Dockyard where more than 400 of the Navy’s ships were built over a period of four centuries, including Lord Nelson’s famous flagship Victory, which took part in the Battle of Trafalgar, and is now moored in Plymouth, Devon.
The Royal Navy left Chatham Dockyard in the late 1980s and developer English Partnerships moved onto the site in the early 1990s and carried out an extensive environmental cleanup. The sea defences were also raised to cater for a 1 in 1000-year flood, prior to Countryside Maritime Ltd making a start on the vast housing development in 1996.
Aarsleff has made numerous visits supplying and driving nearly 100,000 linear metres of mainly 250mm square section precast concrete piles for a combined value approaching £2M. “We have a good working relationship with Aarsleff and are very happy with them and the integrity of their precast piling system,” says Countryside’s project manager Bob Rees. “We’ve been using Aarsleff for many years and never had any problems with them. They always turn up on time, are pretty much self-sufficient, and have done all our piling on this site.
Piling for house builders represents about 40% of Aarsleff precast concrete piling business. “We pride ourselves on our reputation for providing high quality precast concrete piles, which we make in single continuously reinforced sections up to 17m long,” said Aarsleff Piling Managing Director Terry Bolsher, who has 26 years experience in the UK precast pile manufacturing and contracting industry. “The sections can also be quickly and easily joined together onsite using our rigid pretension mechanical steel joints maintaining the integrity of our fully reinforced piles, which have been installed up to 26m long at St Mary’s Island. During work on this site Aarsleff Piling developed and used single length piles up to 17m long, utilising the strength of the company’s rigid fully welded reinforcing cage. Our piles, which have been driven to toe into the underlying very dense sand and gravel, are particularly suited to perform in the site’s very soft overlying waterlogged alluvial clays, which have an undrained shear strength less than 20kNm2. Aarsleff precast piles are ideally suited to this site. They have the in built structural integrity to deal with the site’s unique conditions, the continuity to stay in one piece during installation through up to 12m of very soft alluvial clays and the strength to deal with the loads imposed, both designed and naturally generated. All of this has alleviated the client’s fears for their foundations as opposed to piling systems which are inherently more susceptible to the lack of lateral restraint from the saturated and highly compressible surrounding soils.”
