The document discusses continuous flight auger (CFA) piles, which are formed by drilling and pumping concrete through a hollow stem auger. Key points include: - CFA piling is quiet and vibration-free, making it suitable for sensitive areas. It can form piles in water-bearing soils without casings. - Pile diameters typically range from 300mm to 1200mm, with depths up to 29 meters. Reinforcing cages up to 12 meters are inserted during concreting. - Instrumentation monitors and records the installation process for quality control. Parameters like depth, rotation speed, and concrete pressure are displayed.

1. Piling
Datasheets
Continuous flight auger (CFA)
Driven
Rotary

2. Continuous
Flight Auger
Piles (CFA)
Technical Data The Continuous Flight Auger (CFA)
process is virtually vibration free and one
Application of the quietest forms of piling, making it
Well suited to soft and/or water ideal for environmentally sensitive areas.
bearing ground where deep The method enables piles to be formed in
casings or bentonite suspension
would otherwise be required. water-bearing strata, without the need for
casing or bentonite. It is suitable for
Diameters generally within the constructing piles in most strata: gravels,
range of 300mm to 1200mm with
maximum depths normally up to
sands, silts, clays and soft rocks and in
29 metres. Used for bearing piles mixtures of strata.
and contiguous, interlocking and The original CFA technique allowed
secant piled walls.
for placing a mortar fill. In 1981
Integral enlarged heads Cementation Skanska was the first to
can be formed. extend the process to allow for structural
concrete provision, "CONCORE", and
Advantages
• Quietest known form of piling introduced this to the UK in that same
• Virtually vibration free year.
• All rigs fully instrumented
• Quick and economical
• Limited headroom rigs available Construction Process
CFA piles are formed by drilling to the
Patents required depth using a hollow stem
UK Patent No. 2303868
UK (Div) Patent No. 2328700
continuous flight auger. After reaching the
UK Patent No. 2362665 designed depth, a high slump concrete is
UK Patent No. 2358211 then pumped through the hollow stem.
UK Patent No. 2355750
UK Patent No. 2362912
While the concrete is being pumped, the
UK Patent No. 2356659 auger is withdrawn at a controlled rate,
UK Patent No. 2334543 removing the soil and forming a shaft of
Australia Patent No. 714365 fluid concrete extending to ground level.
USA Patent No. 6116819
USA Patent No. 6168350 A reinforcing cage is then inserted into the
Canada Patent No. 2228518 fluid concrete. Reinforcing cages with
Europe Pub No. 0937825 lengths up to 12 metres are common;
Europe Patent No. 0842329
(Belgium, France, Germany, greater lengths can be installed with the
Ireland, Netherlands, Spain) assistance of cage vibrators.
The Company has a large fleet of CFA
Trademarks rigs. Pile diameters range from 300mm to
AUTO-CFA®
1200mm, and depths of 30 metres or more continuously displays the boring and
CFA-TC®
CFA-PL® are possible giving load capacities up to concreting parameters. During the drilling
CFA-LC® 7500kN. Several patented refinements are phase, the depth of the auger, speed of rotation
CCFA® available related to the use of casings and penetration rate are displayed.
CEM®
(CFA-TC®, CFA-PL® and use in low cut- Subsequently, during the concreting phase a
off piles (CFA-LC®). continuous record of concrete pressure and
rate of pumping is shown; the display is
Instrumentation presented in a manner that highlights under-
To maintain the highest standard of pile supply and over-supply of concrete, compared
construction, Foundations Skanska has with the target value.
undertaken considerable research and On completion of a pile, a computer
development into instrumentation. This printout can be generated for viewing. The full
has resulted in sophisticated computerised data of pile construction details are stored in a
equipment, "AUTO-CFA®", to monitor, data logger module, which is returned at
control and record the CFA pile regular intervals to our Head Office. The data
installation. A computer, positioned in the is then analysed by a separate program, as a
cab directly in front of the operator, further check on the integrity of each pile.
10/07/08
Rev 3

3. Continuous
Flight Auger
Piles (CFA)
Further information Low Headroom
Some rigs in the fleet can be converted to
Cementation Skanska operate in low headroom modes, of 8m,
Maple Cross House 11.5m and 14m clearance. The depths and
Denham Way
diameters which can be achieved in low
Maple Cross
Rickmansworth headroom vary, and require discussion of
Hertfordshire the Client's individual requirements.
WD3 9SW
United Kingdom
Tel: +44 (0)1923 423100 Bored Pile Wall
Fax: +44 (0)1923 423681 Temporary and permanent bored pile
walls can be constructed using the CFA
cementation@skanska.co.uk
www.skanska.co.uk technique. They can be designed to
function as a simple or a propped
Offices cantilever and also to support vertical
Head Office +44 (0)1923 423100
loads.
North +44 (0)1302 821100
The three main types of bored pile
South West, Midlands & Wales
+44 (0)1454 453200
walls which are commonly constructed
Scotland +44 (0)1698 735899
are: Contiguous, Interlocking and Secant.
Northern Ireland +44 (0)28 9024 2746
The selection of a particular type of bored
Republic of Ireland +353 (0)1296 0790
pile wall will depend on the soil and
loading conditions. †
10/07/08
Rev 3

4. Instrumentation
and Automation
of CFA Piling
Technical Data
Application
Monitoring and Control of CFA Pile
construction process.
Provides a permanent record of the
installation process.
Improvement of contract
management through analysis of
pile records.
Suitable for use constructing
Contiguous and Secant walls,
and with Low Headroom rigs.
Advantages
• Operators no longer have to
constantly control the rig,
minimising fatigue
• Operators have additional
freedom to monitor other activities
around the rig, adding to site safety
and efficiency
• The concreting phase is more
reliable when automated, reducing
over supply
of concrete
• Productivity can be increased to a
level where the rig characteristics
determine the limiting elements
• The automatic system provides Automation of CFA Piling assurance of the quality of each installation.
consistency in pile installation and The process of constructing Continuous Computer based systems display and record
reduces the potential for
differential settlement, resulting in Flight Auger (CFA) piles has progressed the significant actions that affect the successful
a more cost effective design, with substantially in recent years and now installation of every pile.
savings for the client represents a major technique in the piling The challenge has been to develop these
Patents
market. systems from a role of recording the pile
UK Patent No 2303 868 Piles are constructed by drilling with a execution details to controlling the process.
UK Patent No 2328 700 continuous flight auger to the required The more advanced instrumentation
International Patent No systems employed record all the relevant data
depth and pumping the concrete through
PCT/GB96/01855
the hollow stem of the auger during its for subsequent examination. It is then possible
Trademarks extraction. Use of this technique, as with to check the installation of every pile either
AUTO-CFA® all piling solutions, is not without risk. manually or automatically and to present the
Construction risks can be minimised once results statistically to evaluate rig-driver
the process is understood and the hazards performance.
addressed. When such a management tool became
Cementation believes that quality available it was apparent that the installation
should never be sacrificed for expediency of CFA piles could be more reliably performed
and has developed CFA piling into a cost using less concrete and in a more cost effective
effective, reliable and efficient method of manner. This promoted the use of real time
installing piles in most ground conditions. displays showing how the installation is
Reliable installation of the pile requires progressing so that the operator can take any
that sufficient concrete is delivered to the necessary corrective action.
auger tip to prevent any ingress of spoil Despite the presentation of real-time
from the walls of the bore which may graphical and numeric displays as guide,
contaminate the cross section of the pile. drivers have been unable to maintain concrete
Reliance is placed on instrumentation injection volumes within 10% of the
to ensure a high level of control and give requirements. As a result, an electronic control
10/07/08
Rev 1

5. Instrumentation
and Automation
of CFA Piling
Further information system has been developed. AUTO-
CFA® replaces the manual operation so
Cementation Skanska that pile installation can be controlled
Maple Cross House automatically by the monitoring
Denham Way computer.
Maple Cross
Rickmansworth To achieve automation, the recipe for
Hertfordshire CFA pile installation has been carefully
WD3 9SW developed by assessing statistically the
United Kingdom
Tel: +44 (0)1923 423100 significant aspects of the process and
Fax: +44 (0)1923 423681 instructing corrective action to be taken
where needed to both increase
cementation@skanska.co.uk
www.skanska.co.uk productivity and enhance pile
performance.
Offices Research has been conducted on both
Head Office +44 (0)1923 423100
the theoretical and practical aspects of
North +44 (0)1302 821100
excavation with a focus on determining
South West, Midlands & Wales
+44 (0)1454 453200
the best boring technique. This has
Scotland +44 (0)1698 735899
culminated in the development of a
process which can consistently maintain
Northern Ireland +44 (0)28 9024 2746
the load bearing capacity of CFA piles.
Republic of Ireland +353 (0)1296 0790
Having proven the success of the
enhanced installation technique which
may be generally adapted to most ground
conditions, the requirements have been
programmed into the control systems on
the piling rig computers to control the
boring and the lifting of the auger.
Automated concreting allows the
progress of the pile installation to match
the speed of auger withdrawal. The target The operators now have additional freedom to
delivery can be adjusted at any time monitor other activities around the rig, adding
during the concreting phase to suit the to site safety and efficiency.
ground conditions.
In addition, any interruptions to the The main benefit of automation of the
concrete delivery, for example when concreting phase is that the process can be
awaiting the next load of concrete, can be carried out reliably. This allows a reduction in
detected automatically and the concreting the over supply of concrete. Productivity can
phase paused until the supply is resumed. be increased to a level where the rig
The key benefit is the speed with which characteristics determine the limiting
the system can react in contrast to elements. These factors are greatly appreciated
operator reaction times. by the piling contractor.
After full evaluation and
commissioning of the first automated rig, The automatic system provides consistency in
the success has been outstanding and a pile installation and reduces the potential for
program of equipping the entire differential settlement, an aspect welcomed by
Cementation fleet of CFA piling rigs is clients. This consistency in pile performance
now in progress. results in a more cost effective design, with
savings for the client
Benefits of Automation
Operators no longer have the strenuous
task of constantly controlling the rig and
are delighted with this simple innovation
which minimises fatigue.
10/07/08
Rev 1

6. Enlarged
Pile Heads
Technical Data
Application
Floor slabs with or without
load transfer platforms or
reinforced granular blankets
Raft foundations with
or without load transfer
platforms or reinforced
granular blankets
Hardstanding areas and road
embankment supports with
load transfer platforms or
reinforced granular blankets
Advantages
• Slab construction
more economical
• Reduces punching shear
• Eliminates expensive
pile trimming
• Barriers and membranes
can be laid over pile heads
• Eliminates expensive
trimming and sealing
Patents
UK Patent No 2334543
UK Patent No 2363152
UK Patent No 2378471
Ireland Patent No 2001/0545
Europe Patent No 0937825
Europe Patent No 1283307
US Patent No 6168350
US Patent No 6168350
US Patent No 6641333
The requirement for integral enlarged pile During the concreting operation a sufficient
heads has increased greatly as a result of head of concrete is maintained, to ensure the
engineers and main contractors looking integrity of the integral enlarged pile head
for the most efficient and economical during the extraction of the head former.
foundation solutions for their clients. Pile reinforcement can project through the
Cementation Skanska has developed a enlarged pile head if required or be terminated
range of specially adapted head formers below the finished head level to meet
for use with DCIS, precast driven or bored particular design requirements.
piling techniques.
Typical Site Applications
The Process Piles are installed on a square or triangular
Specially adapted head formers are driven grid pattern to support the following:
or drilled into the ground at the start of the
piling operation depending on the piling a) Floor slabs with or without load transfer
process in use and the site ground platforms or reinforced granular blankets.
conditions. Formers are generally conical b) Raft foundations with or without load
in shape and up to 900mm in diameter, transfer platforms or reinforced granular
however square heads can also be blankets.
accommodated with certain processes.
10/07/08
Rev 1

7. Enlarged
Pile Heads
Further information c) Hardstanding areas and road As heads are an integral part of the pile
embankment supports with load construction and are finished at ground level,
Cementation Skanska transfer platforms or reinforced expensive pile trimming is eliminated. Under
Maple Cross House granular blankets. slab barrier and/or waterproofing membranes
Denham Way can be laid directly over pile heads so that
Maple Cross
Rickmansworth Advantages expensive cutting and sealing around pile
Hertfordshire The enlarged pile heads reduce the effects shafts is not necessary. †
WD3 9SW of punching shear and therefore more
United Kingdom
Tel: +44 (0)1923 423100 economical slab constructions can be
Fax: +44 (0)1923 423681 used.
cementation@skanska.co.uk
www.skanska.co.uk
Offices Cast-in-Situ Piles with Enlarged Heads
Head Office +44 (0)1923 423100
North +44 (0)1302 821100
Typical Applications
South West, Midlands & Wales Load Transfer Platform or
+44 (0)1454 453200 Reinforced Granular Blanket
Scotland +44 (0)1698 735899
Northern Ireland +44 (0)28 9024 2746
Reinforced
Republic of Ireland +353 (0)1296 0790 Concrete Slab Raft
Foundations
Piles with Enlarged Heads
Load Transfer Platform or
Reinforced Granular Blanket
Embankment
Hardstanding Embankment
Construction Drainage
and Sub-Base Layer
Piles with Enlarged Heads
10/07/08
Rev 1

8. CFA-LC®
Continuous Flight
Auger Piling with
Low Cut-off
Technical Data
Application
Well suited to soft and/or
water bearing ground where
deep casings or bentonite
suspension would otherwise
be required.
Diameters generally within
the range of 600mm to
1200mm with maximum
depths normally up to
27.5 metres.
Used for bearing piles and
contiguous, interlocking
and secant piled walls.
Particularly suitable for
basement construction where
bearing piles are required to
terminate below ground.
Advantages
• Quietest known
form of piling
• Virtually vibration free
• All rigs fully instrumented CFA-LC®
• Quick and economical Low Cut-off CFA Technique
The term “low cut-off” describes piles
Patents
UK Patent No. 2303868 where the finished concrete and
UK (Div) Patent No. 2328700 reinforcing cage levels are several metres
UK Patent No. 2362665 below existing ground. Low cut-off piles
UK Patent No. 2358211
UK Patent No. 2355750 are often specified when the proposed by manually bailing-out the concrete, but the
UK Patent No. 2362912 basement slab level is several metres practical limit is 1-2 metres. Moreover it is
UK Patent No. 2356659 below pile installation level.
Australia Patent No. 714365 generally impractical for the reinforcing cage
USA Patent No. 6116819
The standard CFA piling technique to be pushed down below ground to the
Canada Patent No. 2228518 does not lend itself to achieving low cut- required level.
Europe Patent No. 0842329 offs. Conventionally the full-length
(Belgium, France, Germany,
Cementation Skanska has developed a
hollow stem flight auger is first advanced unique technique which extends the range of
Ireland, Netherlands, Spain)
to founding depth. Concrete is then CFA piling to include true low cut-off levels,
Trademarks pumped through the stem to the base of i.e. concrete and reinforcement. The technique
AUTO-CFA® the pile. The flight auger is slowly
CFA-TC® has been assigned the designation CFA-LC®.
CFA-PL®
withdrawn whilst concrete pumping For this technique a unique casing drive
CFA-LC® continues. The soil carried on the auger is system is used to allow a non-rotating casing
CCFA® removed from the pile head position. to be inserted into the ground at the same time
CEM® After the auger has been completely as the auger is advanced.
removed it is normal to clear the pile head The CFA rig installs the casing, usually to
with a 360º excavator to reveal the below the concrete cut-off level. The auger
concrete at the head of the pile. A then continues to bore to the founding depth.
reinforcing cage is then inserted into the At this stage concrete is pumped through the
concrete. hollow stem to the base of the auger in the
Exceptionally, contractors are normal manner. When the tip of the auger is
sometimes asked to reduce the cast level an agreed distance above the cut-off level, no
of the concrete. This can be carried out further concrete is pumped. The low cut-off
10/07/08
Rev 2

9. CFA-LCTM
Continuous Flight
Auger Piling with
Low Cut-off
Further information can then be achieved by several means, water or bentonite, while the auger is removed.
depending on site conditions. The reinforcing cage is placed as above. The
Cementation Skanska With the simplest method, when the fluid may be pumped through the auger stem,
Maple Cross House concrete has risen to the desired level the or alternatively, down a double-flight
Denham Way auger is removed from the casing by a “bentonite” auger.
Maple Cross
Rickmansworth direct lift. The auger boring head is fitted In yet another variation of the technique,
Hertfordshire with a special flap which retains the soil the concrete can first be placed up to ground
WD3 9SW on the auger, leaving an open cased bore level. The CFA auger is then used to remove
United Kingdom
Tel: +44 (0)1923 423100 above the concrete. The reinforcing cage concrete down to the required depth and the
Fax: +44 (0)1923 423681 can be placed into the casing and if reinforcing cage installed as previously
necessary, pushed down to the required described.
cementation@skanska.co.uk
www.skanska.co.uk level by means of a special attachment Whichever of the three methods is used,
fitted to the flight auger. the rig is then used to withdraw the casing
Offices Alternatively, depending on the nature of which it then transports to another pile
Head Office +44 (0)1923 423100
the underlying strata and the water table, position. With the unique casing drive system
North +44 (0)1302 821100
it may be imprudent to attempt to create there is no need for an attendant service crane
South West, Midlands & Wales
+44 (0)1454 453200
an empty bore in the casing. In these to handle the temporary casing. †
Scotland +44 (0)1698 735899
instances the casing can be flooded with
Northern Ireland +44 (0)28 9024 2746
Republic of Ireland +353 (0)1296 0790
10/07/08
Rev 2

10. CFA-TC®& CFA-PL®
New Continuous
Flight Auger
Piling Techniques
Technical Data
Application
Well suited to soft and/or
water bearing ground where
there is a high risk of bore
instability during construction.
CFA-TCTM particularly suitable
close to structures which may
be affected by standard CFA,
because of loose soil
over hard strata.
CFA-PLTM particularly suitable
to prevent negative skin
friction, and/or provide
protection to concrete
in hard environments.
Diameters generally within
the range of 600mm to
1200mm with maximum
depths normally
up to 27.5 metres.
Used for bearing piles and
contiguous, interlocking
and secant piled walls.
Particularly suitable for CFA-TC® & CFA-PL®
basement construction where
bearing piles are required to
Two New CFA Techniques
terminate below ground. Cementation Skanska has developed two
new techniques which extend the range of
Advantages from the sides of the bore. This phenomenon
• Quietest known
CFA application. The techniques have
been assigned the designations CFA-TC® can cause damage to adjacent structures,
form of piling
• Virtually vibration free and CFA-PL®. whether above or below ground.
• All rigs fully instrumented Both techniques are patented and both The CFA-TC® technique installs a casing,
• Quick and economical to a suitable depth, during the advance of the
make use of a unique casing installation
Patents system. This allows a non-rotating casing flight auger and this prevents the auger from
UK Patent No. 2303868 to be inserted into the ground at the same flighting the softer overlying strata.
UK (Div) Patent No. 2328700 The CFA rig installs the casing, completes the
UK Patent No. 2362665 time as the auger is advanced.
UK Patent No. 2358211
bore to founding depth and then removes the
UK Patent No. 2355750 CFA-TC® casing at the end of the concreting phase. It
UK Patent No. 2362912 then moves to another pile position. There is
UK Patent No. 2356659
This refers to the use of a temporary
casing during CFA pile construction, and no need for an attendant service crane to
Australia Patent No. 714365
USA Patent No. 6116819 virtually eliminates settlement of the handle the temporary casing.
Canada Patent No. 2228518
surrounding soil. The effectiveness of the new CFA-TC®
Europe Patent No. 0842329 technique is demonstrated overleaf, showing
(Belgium, France, Germany, A well-known problem, sometimes
Ireland, Netherlands, Spain) called 'flighting' can occur when the upper the measured settlement of the ground
strata is relatively loose or soft compared surrounding CFA piles, at two sites with
Trademarks similar ground conditions, in Glasgow.
AUTO-CFA® with the underlying founding strata. In
Where no casing was used, settlement at a
CFA-TC® these conditions the rate of advance of the
CFA-PL® auger (per revolution) can be much less in distance of 1m from the piles was 13.8 mm.
CFA-LC® the underlying strata than in the 'softer' Settlement decreased further away from the
CCFA® piles, but could still be detected up to a
CEM® overlying strata. The auger, which acts as
a vertical conveyor, tends to draw soil distance of approximately 14 metres.
10/07/08
Rev 2

11. CFA-TCTM & CFA-PLTM
New Continuous
Flight Auger
Piling Techniques
Further information In contrast, when a casing was installed CFA-PL®
by the CFA-TC® technique, settlement at This technique refers to the installation of a
Cementation Skanska four points each a distance of 1m behind a permanent liner during the construction of a
Maple Cross House piled wall. It gave an average of 1mm, CFA pile.
Denham Way
over a period of eight days of piling. Permanent liners may be required for one
Maple Cross
Rickmansworth Further advantage of the CFA-TC® of several reasons, as follows:
Hertfordshire
WD3 9SW technique is the ability to position piles
more accurately than without casing. At • to protect the concrete in aggressive ground
United Kingdom
Tel: +44 (0)1923 423100 the Glasgow contract the average plan conditions
Fax: +44 (0)1923 423681
deviation at ground level, of the 75 wall • to avoid the effects of 'downdrag' caused
piles installed, was 24mm from true by ground settlement.
cementation@skanska.co.uk
www.skanska.co.uk position. Verticality was also better than • to avoid loading adjacent structures and
for uncased piles. services, often below ground.
Offices
Head Office +44 (0)1923 423100
The wall thickness of the permanent liner will
North +44 (0)1302 821100 UNCASED CFA PIL E, CADOG AN STREET, GL ASG OW be determined by the specific site conditions.
South West, Midlands & Wales
+44 (0)1454 453200
0
The use of a steel liner coated with a
-2
bituminous layer, often called a 'slip layer', can
G RO UND SETTLEMENT (m m)
Scotland +44 (0)1698 735899 -4
Northern Ireland +44 (0)28 9024 2746 -6
prevent all three of the above problems.
Alternatively a plastic liner can be used in
Republic of Ireland +353 (0)1296 0790
-8
-10 place of the coated steel liner.
With the CFA-PL® technique these
-12
-14
-16 permanent liners can be installed by the CFA
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
DISTANCE F ROM PILE (m ) rig during pile construction. The casing drive
system (referred to earlier) requires little
3
2 modification to be used for installation of
1
0
-1
permanent liners. Because the liners are
-2
-3
installed at the same time as the pile is bored,
-4
-5 there is no annular gap around the liner, i.e. it
is in intimate contact with the soil. †
1 2 3 4 5 6 7 8
D AY S
C A SED C FA PILIN G, A TLA N TIC QU A Y , GLA SGOW
10/07/08
Rev 2

12. Cementation Skanska
Maple Cross House
Denham Way
Maple Cross
Rickmansworth
Hertfordshire
WD3 9SW
Tel: 01923 423100
www.skanska.co.uk