cased cfa rev1
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Cased CFAFirst to use this technique in the UK
22/10/13 Rev 1
Further information:Cementation Skanskaskanska.co.uk/cementation
The Cased Continuous Flight Auger (Trade Name:
DKS) is a modied version of the traditional
Continuous Flight Auger (CFA) process. It
commands superior cutting power and can achieve
better construction tolerances and better pile
surface appearance, compared to the standard CFA
process.
It is virtually vibration free and one of the
quietest forms of piling, making it ideal for
environmentally sensitive areas. The method
enables piles to be formed in water-bearing strata,
without the need for bentonite support.
Cementation Skanska was the rst in the UK to
operate a 1m diameter Bauer BG40-DKS system
in 2011. This system can install piles up to 16.5m
deep.
Construction ProcessCased CFA piles are formed by drilling to the
required depth using a string of hollow stem
continuous ight auger drill string, encased within
a string of segmental casing of equal length. They
rotate independently and in opposite directions to
assist spoil transport upwards. The spoil exits the
top of the drill string and is guided by a spoil chute
to ground level.
The business end of the casing is armoured with
tungsten tipped cutting teeth. Similarly the boring
head of the auger is equipped with bullet-shaped
ApplicationCan be used on various walltypes, either contiguous,interlocking or secant,on deep or load bearing
foundations
Advantages Construction tolerances
and surface appearancebetter than conventionalCFA piling
Fast installation Virtually vibration free Used without bentonite
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rock cutting teeth. These allow the system to
cut into hard soil stratum or un-reinforced rmconcrete.
After reaching the designed depth, a high slump
concrete is pumped through the hollow stem of
the drill string. The drill string and casing are
withdrawn together at a controlled rate as concrete
pumping continues until ground level to form a
shaft of uid concrete.
A reinforcement cage is then inserted into the
uid concrete. Cages of length up to 12 metres are
common. However cages of up to 16m length can
be installed with the aid of mechanical vibration.
InstrumentationTo maintain the highest standard of pile quality
control, the drilling and concreting process is
monitored and recorded continuously with an
on-board computer control system, B-Tronics.
Quality critical information is continuously
displayed in real time onto a touch screen directly
in front of the operator in the cab. During the
drilling phase, the current depth, speed of rotation
and penetration rate are displayed. Subsequently,during the concreting phase a continuous record of
concrete pressure and rate of pumping is shown;
the display is presented in a manner that highlights
under / over-supply of concrete, compared with a
target value.
On completion of a pile, a computer record of the
drilling / concreting process can be generated for
viewing. The raw data can be transferred from the
rig to a personal computer for detailed analysis as
part of the QA process.
Piled Retaining WallOne common application of the Cased CFA system
is in the construction of piled retaining walls. The
wall types can be either contiguous, interlocking or
secant. They can be designed to function to retain
deep excavations and also to support vertical loads.
The Cased CFA system can match the product
quality of a traditional bored pile wall, whilst
offering higher productivity.