A cased piling rig thought to be the UK’s largest has been in action in London. NCE reports
Miller Piling has raised the bar for continuous flight auger (CFA) piling in the UK with the introduction of a 140t machine from Italian manufacturer Casagrande. The new C850 DH rig can install piles up to 1,000mm in diameter to a depth of more than 21m, and is believed to be the largest cased CFA rig in the UK.
Miller ordered the new rig to satisfy a number of large piling contracts due to come on stream this year, and it was delivered in November 2012.
It has already completed its first task: installing a secant piled retaining wall for the basement of a new residential development in Stratford, east London.
“Lots of developers now want deep basements and, in tight urban sites, cased CFA piling really comes into its own”
James Hayward, Miller Piling
This project, for housing developer Telford Homes, involves constructing a two storey basement beneath what will be a 26-storey luxury development of one, two and three-bedroom apartments.
Miller won the contract on the basis of its capability to deliver a full package that included installing the pile capping beam, designing the temporary works and bulk excavation of the basement, in addition to the piling itself.
Cased CFA piling is a fast growing sector of the foundation industry. It involves drilling to the required depth with a continuous casing and hollow stemmed flight auger, and then pumping liquid concrete down the hollow stem while the casing and auger is slowly withdrawn, conveying the soil upward along the flights. Reinforcement can then be lowered into the column of liquid concrete
Miller’s new Casagrande rig is a cased CFA machine, which means it can drive both the auger and a full length steel pile casing simultaneously.
The auger runs inside a 21m casing, which is spun into the ground along with the auger,” explains Miller technical manager James Hayward.
The method is particularly useful for constructing deep basements in poor ground conditions, as it prevents the auger from deviating from the intended path. This is especially important when constructing a secant piled wall, where accurate alignment is essential.
“These types of rigs are typically larger than conventional piling machines because of the force needed to twist the casing and auger into the ground. This machine has two rotary motors, which have a drilling torque capacity of 360kNm and 421kNm,” says Hayward.
Cased CFA piling was chosen for the Stratford project because the ground is too wet, variable and unstable for normal bored piles. Using traditional piling techniques would have also been painfully slow in these conditions.
Using the new C850 rig, Miller installed 130 piles, each 900mm in diameter, in little more than a month, achieving up to eight per day. “You’d be lucky to install one a day with traditional piling,” says Hayward.
This method of piling is becoming increasingly popular in the UK, especially in cities, because it causes minimal noise and vibration. “Lots of developers now want deep basements and, as projects such as this one are often in tight urban sites, cased CFA piling really comes into its own,” says Hayward.
Having spent most of December on the Telford Homes site, the C850 is now working on another commercial development in London. Meanwhile, Miller remains on site in Stratford where bulk excavation and installation of the pile capping beam is now underway.