Piling Datasheets. Continuous flight auger (CFA) Driven Rotary

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Piling

Datasheets

Continuous flight auger (CFA)

Driven

Rotary

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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 300mm to 1200mm with maximum depths normally up to 29 metres. Used for bearing piles and contiguous, interlocking and secant piled walls. Integral enlarged heads can be formed.

Advantages

• Quietest known form of piling • Virtually vibration free • All rigs fully instrumented • Quick and economical • Limited headroom rigs available

Patents

UK Patent No. 2303868 UK (Div) Patent No. 2328700 UK Patent No. 2362665 UK Patent No. 2358211 UK Patent No. 2355750 UK Patent No. 2362912 UK Patent No. 2356659 UK Patent No. 2334543 Australia Patent No. 714365

USA Patent No. 6116819 USA Patent No. 6168350 Canada Patent No. 2228518

Europe Pub No. 0937825 Europe Patent No. 0842329 (Belgium, France, Germany, Ireland, Netherlands, Spain)

Trademarks AUTO-CFA® CFA-TC® CFA-PL® CFA-LC® CCFA® CEM®

continuously displays the boring and concreting parameters. During the drilling phase, the depth of the auger, 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-supply and over-under-supply of concrete, compared with the target value.

On completion of a pile, a computer printout can be generated for viewing. The full data of pile construction details are stored in a data logger module, which is returned at regular intervals to our Head Office. The data is then analysed by a separate program, as a further check on the integrity of each pile.

The Continuous Flight Auger (CFA) process 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 casing or bentonite. It is suitable for constructing piles in most strata: gravels, sands, silts, clays and soft rocks and in mixtures of strata.

The original CFA technique allowed for placing a mortar fill. In 1981 Cementation Skanska was the first to extend the process to allow for structural concrete provision, "CONCORE", and introduced this to the UK in that same year.

Construction Process

CFA piles are formed by drilling to the required depth using a hollow stem continuous flight auger. After reaching the designed depth, a high slump concrete is then pumped through the hollow stem. While the concrete is being pumped, the auger is withdrawn at a controlled rate, removing the soil and forming a shaft of fluid concrete extending to ground level. A reinforcing cage is then inserted into the fluid concrete. Reinforcing cages with lengths up to 12 metres are common; greater lengths can be installed with the assistance of cage vibrators.

The Company has a large fleet of CFA rigs. Pile diameters range from 300mm to 1200mm, and depths of 30 metres or more are possible giving load capacities up to 7500kN. Several patented refinements are available related to the use of casings (CFA-TC®_{, CFA-PL}®_{and use in low} cut-off piles (CFA-LC®_).

Instrumentation

To maintain the highest standard of pile construction, Foundations Skanska has undertaken considerable research and development into instrumentation. This has resulted in sophisticated computerised equipment, "AUTO-CFA®", to monitor, control and record the CFA pile

installation. A computer, positioned in the cab directly in front of the operator,

Continuous

Flight Auger

Piles (CFA)

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Further information

Cementation Skanska

Maple Cross House Denham Way Maple Cross Rickmansworth Hertfordshire WD3 9SW United Kingdom Tel: +44 (0)1923 423100 Fax: +44 (0)1923 423681 cementation@skanska.co.uk www.skanska.co.uk Offices Head Office +44 (0)1923 423100 North +44 (0)1302 821100 South West, Midlands & Wales +44 (0)1454 453200 Scotland +44 (0)1698 735899 Northern Ireland +44 (0)28 9024 2746 Republic of Ireland +353 (0)1296 0790

Low Headroom

Some rigs in the fleet can be converted to operate in low headroom modes, of 8m, 11.5m and 14m clearance. The depths and diameters which can be achieved in low headroom vary, and require discussion of the Client's individual requirements. Bored Pile Wall

Temporary and permanent bored pile walls can be constructed using the CFA technique. They can be designed to function as a simple or a propped cantilever and also to support vertical loads.

The three main types of bored pile walls which are commonly constructed are: Contiguous, Interlocking and Secant. The selection of a particular type of bored pile wall will depend on the soil and loading conditions. †

Continuous

Flight Auger

Piles (CFA)

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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 consistency in pile installation and reduces the potential for differential settlement, resulting in a more cost effective design, with savings for the client

Patents UK Patent No 2303 868 UK Patent No 2328 700 International Patent No PCT/GB96/01855 Trademarks AUTO-CFA®

assurance of the quality of each installation. Computer based systems display and record the significant actions that affect the successful installation of every pile.

The challenge has been to develop these systems from a role of recording the pile execution details to controlling the process.

The more advanced instrumentation systems employed record all the relevant data for subsequent examination. It is then possible to check the installation of every pile either manually or automatically and to present the results statistically to evaluate rig-driver performance.

When such a management tool became available it was apparent that the installation of CFA piles could be more reliably performed using less concrete and in a more cost effective manner. This promoted the use of real time displays showing how the installation is progressing so that the operator can take any necessary corrective action.

Despite the presentation of real-time graphical and numeric displays as guide, drivers have been unable to maintain concrete injection volumes within 10% of the

requirements. As a result, an electronic control Automation of CFA Piling

The process of constructing Continuous Flight Auger (CFA) piles has progressed substantially in recent years and now represents a major technique in the piling market.

Piles are constructed by drilling with a continuous flight auger to the required depth and pumping the concrete through the hollow stem of the auger during its extraction. Use of this technique, as with all piling solutions, is not without risk. Construction risks can be minimised once the process is understood and the hazards addressed.

Cementation believes that quality should never be sacrificed for expediency and has developed CFA piling into a cost effective, reliable and efficient method of installing piles in most ground conditions. Reliable installation of the pile requires that sufficient concrete is delivered to the auger tip to prevent any ingress of spoil from the walls of the bore which may contaminate the cross section of the pile.

Reliance is placed on instrumentation to ensure a high level of control and give

Instrumentation

and Automation

of CFA Piling

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Further information

The operators now have additional freedom to monitor other activities around the rig, adding to site safety and efficiency.

The main benefit of automation of the concreting phase is that the process can be carried out reliably. This allows a reduction in the over supply of concrete. Productivity can be increased to a level where the rig

characteristics determine the limiting

elements. These factors are greatly appreciated by the piling contractor.

The automatic system provides consistency in pile installation and reduces the potential for differential settlement, an aspect welcomed by clients. This consistency in pile performance results in a more cost effective design, with savings for the client

system has been developed. AUTO-CFA® replaces the manual operation so that pile installation can be controlled automatically by the monitoring computer.

To achieve automation, the recipe for CFA pile installation has been carefully developed by assessing statistically the significant aspects of the process and instructing corrective action to be taken where needed to both increase

productivity and enhance pile performance.

Research has been conducted on both the theoretical and practical aspects of excavation with a focus on determining the best boring technique. This has culminated in the development of a process which can consistently maintain the load bearing capacity of CFA piles.

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 delivery can be adjusted at any time during the concreting phase to suit the ground conditions.

In addition, any interruptions to the concrete delivery, for example when awaiting the next load of concrete, can be detected automatically and the concreting phase paused until the supply is resumed. The key benefit is the speed with which the system can react in contrast to operator reaction times.

After full evaluation and

commissioning of the first automated rig, the success has been outstanding and a program of equipping the entire Cementation fleet of CFA piling rigs is now in progress.

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.

Instrumentation

and Automation

of CFA Piling

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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

During the concreting operation a sufficient head of concrete is maintained, to ensure the integrity of the integral enlarged pile head during the extraction of the head former.

Pile reinforcement can project through the enlarged pile head if required or be terminated below the finished head level to meet

particular design requirements.

Typical Site Applications

Piles are installed on a square or triangular grid pattern to support the following:

a) Floor slabs with or without load transfer platforms or reinforced granular blankets. b) Raft foundations with or without load

transfer platforms or reinforced granular blankets.

The requirement for integral enlarged pile heads has increased greatly as a result of engineers and main contractors looking for the most efficient and economical foundation solutions for their clients. Cementation Skanska has developed a range of specially adapted head formers for use with DCIS, precast driven or bored piling techniques.

The Process

Specially adapted head formers are driven or drilled into the ground at the start of the piling operation depending on the piling process in use and the site ground conditions. Formers are generally conical in shape and up to 900mm in diameter, however square heads can also be accommodated with certain processes.

Enlarged

Pile Heads

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Embankment Drainage Layer Hardstanding Construction and Sub-Base Embankment

Piles with Enlarged Heads Load Transfer Platform or Reinforced Granular Blanket

Cast-in-Situ Piles with Enlarged Heads Typical Applications

Piles with Enlarged Heads Reinforced

Concrete Slab

Load Transfer Platform or Reinforced Granular Blanket

Raft Foundations c) Hardstanding areas and road

embankment supports with load transfer platforms or reinforced granular blankets.

Advantages

The enlarged pile heads reduce the effects of punching shear and therefore more economical slab constructions can be used.

Further information

As heads are an integral part of the pile construction and are finished at ground level, expensive pile trimming is eliminated. Under slab barrier and/or waterproofing membranes can be laid directly over pile heads so that expensive cutting and sealing around pile shafts is not necessary.†

Enlarged

Pile Heads

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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 • Quick and economical

Patents

UK Patent No. 2303868 UK (Div) Patent No. 2328700 UK Patent No. 2362665 UK Patent No. 2358211 UK Patent No. 2355750 UK Patent No. 2362912 UK Patent No. 2356659 Australia Patent No. 714365

USA Patent No. 6116819 Canada Patent No. 2228518 Europe Patent No. 0842329 (Belgium, France, Germany, Ireland, Netherlands, Spain)

by manually bailing-out the concrete, but the practical limit is 1-2 metres. Moreover it is generally impractical for the reinforcing cage to be pushed down below ground to the required level.

Cementation Skanska has developed a unique technique which extends the range of CFA piling to include true low cut-off levels, i.e. concrete and reinforcement. The technique has been assigned the designation CFA-LC®. For this technique a unique casing drive system is used to allow a non-rotating casing to be inserted into the ground at the same time as the auger is advanced.

The CFA rig installs the casing, usually to below the concrete cut-off level. The auger then continues to bore to the founding depth. At this stage concrete is pumped through the hollow stem to the base of the auger in the normal manner. When the tip of the auger is an agreed distance above the cut-off level, no further concrete is pumped. The low cut-off CFA-LC®

Low Cut-off CFA Technique

The term “low cut-off” describes piles where the finished concrete and

reinforcing cage levels are several metres below existing ground. Low cut-off piles are often specified when the proposed basement slab level is several metres below pile installation level.

The standard CFA piling technique does not lend itself to achieving low cut-offs. Conventionally the full-length hollow stem flight auger is first advanced to founding depth. Concrete is then pumped through the stem to the base of the pile. The flight auger is slowly withdrawn whilst concrete pumping continues. The soil carried on the auger is removed from the pile head position. After the auger has been completely removed it is normal to clear the pile head with a 360º excavator to reveal the concrete at the head of the pile. A reinforcing cage is then inserted into the concrete.

Exceptionally, contractors are sometimes asked to reduce the cast level of the concrete. This can be carried out

CFA-LC

®

Continuous Flight

Auger Piling with

Low Cut-off

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Further information

water or bentonite, while the auger is removed. The reinforcing cage is placed as above. The fluid may be pumped through the auger stem, or alternatively, down a double-flight “bentonite” auger.

In yet another variation of the technique, the concrete can first be placed up to ground level. The CFA auger is then used to remove concrete down to the required depth and the reinforcing cage installed as previously described.

Whichever of the three methods is used, the rig is then used to withdraw the casing which it then transports to another pile position. With the unique casing drive system there is no need for an attendant service crane to handle the temporary casing. †

can then be achieved by several means, depending on site conditions.

With the simplest method, when the concrete has risen to the desired level the auger is removed from the casing by a direct lift. The auger boring head is fitted with a special flap which retains the soil on the auger, leaving an open cased bore above the concrete. The reinforcing cage can be placed into the casing and if necessary, pushed down to the required level by means of a special attachment fitted to the flight auger.

Alternatively, depending on the nature of the underlying strata and the water table, it may be imprudent to attempt to create an empty bore in the casing. In these instances the casing can be flooded with

CFA-LC

TM

Continuous Flight

Auger Piling with

Low Cut-off

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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 basement construction where bearing piles are required to terminate below ground.

Advantages

• Quietest known form of piling • Virtually vibration free • All rigs fully instrumented • Quick and economical

Patents

UK Patent No. 2303868 UK (Div) Patent No. 2328700 UK Patent No. 2362665 UK Patent No. 2358211 UK Patent No. 2355750 UK Patent No. 2362912 UK Patent No. 2356659 Australia Patent No. 714365

USA Patent No. 6116819 Canada Patent No. 2228518 Europe Patent No. 0842329 (Belgium, France, Germany, Ireland, Netherlands, Spain)

from the sides of the bore. This phenomenon can cause damage to adjacent structures, whether above or below ground.

The CFA-TC® technique installs a casing, to a suitable depth, during the advance of the flight auger and this prevents the auger from flighting the softer overlying strata.

The CFA rig installs the casing, completes the bore to founding depth and then removes the casing at the end of the concreting phase. It then moves to another pile position. There is no need for an attendant service crane to handle the temporary casing.

The effectiveness of the new CFA-TC® technique is demonstrated overleaf, showing the measured settlement of the ground surrounding CFA piles, at two sites with similar ground conditions, in Glasgow.

Where no casing was used, settlement at a distance of 1m from the piles was 13.8 mm. Settlement decreased further away from the piles, but could still be detected up to a distance of approximately 14 metres. CFA-TC®_{& CFA-PL}®

Two New CFA Techniques

Cementation Skanska has developed two new techniques which extend the range of CFA application. The techniques have been assigned the designations CFA-TC® and CFA-PL®.

Both techniques are patented and both make use of a unique casing installation system. This allows a non-rotating casing to be inserted into the ground at the same time as the auger is advanced.

CFA-TC®

This refers to the use of a temporary casing during CFA pile construction, and virtually eliminates settlement of the surrounding soil.

A well-known problem, sometimes called 'flighting' can occur when the upper strata is relatively loose or soft compared with the underlying founding strata. In these conditions the rate of advance of the auger (per revolution) can be much less in the underlying strata than in the 'softer' overlying strata. The auger, which acts as a vertical conveyor, tends to draw soil

CFA-TC

®

& CFA-PL

®

New Continuous

Flight Auger

Piling Techniques

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Further information

CFA-PL®

This technique refers to the installation of a permanent liner during the construction of a CFA pile.

Permanent liners may be required for one of several reasons, as follows:

• to protect the concrete in aggressive ground conditions

• to avoid the effects of 'downdrag' caused by ground settlement.

• to avoid loading adjacent structures and services, often below ground.

The wall thickness of the permanent liner will be determined by the specific site conditions.

The use of a steel liner coated with a bituminous layer, often called a 'slip layer', can prevent all three of the above problems.

Alternatively a plastic liner can be used in place of the coated steel liner.

With the CFA-PL® technique these permanent liners can be installed by the CFA rig during pile construction. The casing drive system (referred to earlier) requires little modification to be used for installation of permanent liners. Because the liners are installed at the same time as the pile is bored, there is no annular gap around the liner, i.e. it is in intimate contact with the soil. †

In contrast, when a casing was installed by the CFA-TC® technique, settlement at four points each a distance of 1m behind a piled wall. It gave an average of 1mm, over a period of eight days of piling.

Further advantage of the CFA-TC® technique is the ability to position piles more accurately than without casing. At the Glasgow contract the average plan deviation at ground level, of the 75 wall piles installed, was 24mm from true position. Verticality was also better than for uncased piles.

CFA-TC

TM

& CFA-PL

TM

New Continuous

Flight Auger

Piling Techniques

UNCASED CFA PIL E, CADOG AN STREET, GL ASG OW

-16 -14 -12 -10 -8 -6 -4 -2 0 1 2 3 4 5 6 7 8 9 10 11 12 1 3 14 15 DISTANCE F ROM PILE (m )

G R O U N D SET T L EM EN T (m m )

C A SED C FA PI LI N G, A TLA N TI C QU A Y , GLA SGOW

-5 -4 -3 -2 -1 0 1 2 3 1 2 3 4 5 6 7 8 D A Y S

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Cementation Skanska

Maple Cross House

Denham

Way

Maple

Cross

Rickmansworth