Short squat piles are helping to transform an area of south-east London into a vibrant new residential development. Declan Lynch reports.
The complete redevelopment of Kidbrooke Park is a project one former resident of the south-east London suburb would applaud: Changing Rooms frontman Lawrence Llewelyn Bowen.
The work currently being carried out is part of a 20-year regeneration project consisting of more than 4,000 new homes and the demolition of the Ferriers estate, which was built in 1972.
Phase one is well under way and the first residents will begin moving into 449 homes, 229 of which will be affordable housing, over the summer.
Subcontractor May Gurney is installing the piles for blocks D and G, which will form the base for two four-storey buildings each consisting of 39 apartments. The piles are located over an artesian aquifer so have to be short and squat to withstand the high loads from the building whilst not penetrating it.
Continuous flight auger (CFA) piles were chosen for this site because they are quieter to install than other forms of piling. Noise is a concern because the site is within 30m of a residential area.
“It is a relatively straightforward job, but due to the size of the site it can be logistically quite difficult to get everyone in place,” says May Gurney site foreman Daniel Lansdowne.
The ground profile consists of 1m crushed concrete platform overlaying stiff clay and below that sits the aquifer.
“Clay is easier to work with because it is stiff and compact and there is less chance of one pile slumping into another,” adds Lansdowne.
The process involves drilling with a long, hollow stem auger to the required depth. Steel reinforcement bars are then inserted into the concrete while it cures.
Then C25/30 concrete is pumped into the hole through the stem, at the same time the auger is slowly withdrawn lifting the spoil out of the hole and forming the pile.
The ground is then levelled and the pile is checked to see it is in the right position.
“The levels are quite high in this job. Some of the piles need to be broken down by up to 3.8m. We put foam on the reinforcement 150mm above the depth of where the pile needs to broken down to help break the concrete,” says Lansdowne.
May Gurney is installing 191, 750mm diameter piles to a depth of 7.5m on block G. The steel reinforcing cage consists of 6T32 bars, some of which are fitted with steel collars to withstand horizontal loads.
“We are installing 12- 15 piles per day, but they are at different depths, and the cages are being assembled on site”
On block D, the firm is installing 81, 900mm diameter piles and 118, 1.05m diameter CFA piles to a depth of 10m. They are to cope with a compression load of between 900kN and 1,175kN. Work was completed last week and the contract value is £350,000.
“It is a tight timescale to site all the piles. We are installing 12-15 piles per day, but they are at different depths, and the cages are being assembled on site,” adds Lansdowne.
May Gurney has installed redundant and working test piles to ensure they are working properly and will not penetrate the artesian aquifer below. The piles are tested 24 hours after installation to ensure they are strong enough.
To complete the project on time the subcontractor has 10 people working on the project including steel fixer Lawrence and Son, who have been preparing all the cages on site.
Piling for blocks D and G is due to finish before the end of this month, but as the project will take up to 20 years to complete meaning there is plenty of groundwork still to do.
Piling special: Capital procedures in south-east London