Essex-based specialist Central Piling is placing more than 80 piles in a tight basement while demolition contractors work above. Paul Thompson reports.
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The Kilburn High Road in north-west London is one of the capital’s busier road routes. Regularly rigid with traffic this particular part of the A5 helps ferry commuters from some of London’s leafiest suburbs.
Some way along the busy radial route specialist contractor Central Piling is crammed into the basement of numbers 146- 162, installing piles as part of a contract with main contractor Kind & Company.
“We needed to reinforce and prop the stairwell as well as ramp it with crushed material to be able to squeeze the rig down there”
In a bid to cut back on the overall construction period on the scheme Central Piling is carrying out its contract to install 88 of these piles with diameters of 300mm to 400mm in the basement of the building while demolition work continues.
But with the final piles required to take loads of up to 1,000kN structural engineer Kirk Saunders Associates had indicated that piles of 400mm diameter at a depth of almost 24m through the underlying London Clay would be required at the mixed use development - way beyond the capability of most mini piling rigs, according to Central Piling managing director Steve Hadley.
“There are smaller rigs available but we needed to maximise the rig size to give ourselves a chance of installing piles of that sort of scale,” he says.
The team selected a 5t Hutte 203 rig capable of delivering 2.5 tonne metres coupled with a 3.1m mast height to install the open hole auger piles at the site.
Even by removing the head at the top of the mast the team were working tight up against the soffit of the reinforced concrete floor slab during installation ensuring that auger sections were kept to a maximum of 1m.
The team also had to carry out some rudimentary structural alterations to the basement as the Hutte piling rig was shoe-horned down the concrete stairwell.
“We needed to reinforce and prop the stairwell as well as ramp it with crushed material to be able to squeeze the rig down there. We even needed to break out some of the render on the walls to just gain an extra few millimetres,” says Hadley.
As part of the design by structural engineer Kirk Saunders Associates some of the piles had been located tight against existing adjacent and party walls.
But thanks to a recent clarification of the Provision and Use of Work Equipment Regulations by the Health and Safety Executive, which requires a shield to be used at 1.1m around the auger, some of these pile locations had to be revised.
“In some places we had to rotate pile cap positions so that the piles themselves were far enough away from walls to allow the rig guarding to open for the placement of auger sections,” Hadley says, adding: “The latest interpretation of the regulations mean we can’t get quite as tight to walls as we could before but there was never any need to rake any piles over.”
Fitted with a stationary power pack the Hutte rig is being used alongside an excavator and dumper which in such a confined space has caused the site team problems in venting the exhaust fumes.
A bespoke fume extraction system fitted to the power pack coupled with two, 350mm air vents makes sure that the site installation team can continue to work in a bid to meet its six-week project completion timetable.