CFA Vs SFA. Whats The Difference?

Continuous Flight Auger (CFA) and Sectional Flight Auger (SFA) piling are both bored, cast-in-place piling methods used to create deep foundations. With both systems, an auger excavates the ground before concrete or grout is placed into the bore and reinforcement is installed. The principal difference is the way the auger is configured and how the pile is installed. CFA piling uses one continuous auger and is generally suited to open sites with sufficient access and headroom. SFA piling uses shorter auger sections that are progressively connected, making it suitable for restricted-access and low-headroom projects. Understanding the differences between CFA and SFA piling helps determine which method may provide the safest, most practical and most cost-effective solution for a particular site.

CFA vs SFA Piling at a Glance

Consideration	CFA Piling	SFA Piling
Auger arrangement	Uses one continuous auger to reach the complete pile depth.	Uses shorter auger sections that are progressively added and removed.
Rig size	Generally requires a larger and taller piling rig.	Can be installed using smaller and more compact piling equipment.
Headroom	Best suited to open sites with unrestricted working height.	Suitable for low-headroom, internal and confined working areas.
Access	Requires access suitable for the rig, concrete pump and supporting equipment.	Can be selected where narrow access routes or difficult site logistics prevent a larger rig from operating.
Installation speed	Generally faster because drilling and concreting take place in one continuous operation.	Normally slower because auger sections must be connected and removed individually.
Concrete placement	Concrete or grout is pumped through the hollow auger stem as it is withdrawn.	May use either a hollow-stem or solid-stem installation method, depending on the ground conditions.
Typical application	Open, higher-output and larger-volume piling projects.	Restricted-access, low-headroom, internal and smaller-volume projects.
Noise and vibration	Low-noise and almost vibrationless bored installation.	Low-noise and almost vibrationless bored installation.
Retaining walls	Can be used to install contiguous bored pile walls.	Can also form contiguous bored pile walls where access or headroom is restricted.

What Do CFA and SFA Piling Have in Common?

CFA and SFA piles are both formed by boring into the ground using a rotating auger. Both methods can provide:

Bored, cast-in-place reinforced concrete piles
Low-noise installation
Minimal vibration compared with many driven piling methods
Support for compressive, tensile and shear loads
A range of pile diameters and depths
Foundation solutions close to existing buildings and sensitive infrastructure
Bearing piles for buildings and structures
Contiguous bored pile retaining walls

With both systems, the pile design must reflect the structural loads, ground conditions, required depth, pile diameter and practical constraints of the site. The most suitable method cannot therefore be selected from access or programme considerations alone.

How Does CFA Piling Work?

Continuous Flight Auger piling uses a hollow-stem auger long enough to reach the complete pile depth in one continuous drilling operation. The auger is rotated into the ground until the required depth is achieved. Concrete or grout is then pumped through the hollow centre of the auger as it is steadily withdrawn. This replaces the excavated soil with a continuous column of wet concrete. The required reinforcement is then plunged into the completed pile. The process generally involves:

Positioning the CFA rig over the pile location
Drilling to the required design depth in one continuous stroke
Pumping concrete or grout through the auger stem
Withdrawing the auger at a controlled rate
Plunging reinforcement into the wet concrete
Preparing the completed pile for its structural connection

Because the pile is drilled and concreted in one continuous process, CFA piling can achieve a high rate of production where the site has sufficient space and headroom. For more detailed information, read What Is CFA Piling and When Is It Used?

How Does SFA Piling Work?

Sectional Flight Auger piling uses shorter, individual auger sections rather than one continuous auger. Installation begins with a lead auger, also known as the boring head. Additional auger sections are then progressively connected as drilling advances. Once the design depth has been reached, the sections are withdrawn and removed individually. SFA piles can be installed using either:

A hollow-stem method, where concrete or grout is pumped through the auger as it is withdrawn
A solid-stem method, where the augers are removed before concrete is placed into a stable, open bore

The reinforcement is then installed in accordance with the pile design and installation sequence. Using shorter auger sections allows the equipment to operate beneath roofs, floors, bridges, power lines and other overhead restrictions. Smaller SFA rigs can also access sites where the route is too narrow or complex for larger CFA equipment. Read the full guide: What Is Sectional Flight Auger Piling and When Is It Used?

What Is the Main Difference Between CFA and SFA?

The main difference is whether the auger is continuous or assembled in shorter sections. A CFA rig carries the full auger length vertically on its mast. This makes the installation process fast, but it requires sufficient headroom and a suitable access route for a relatively large rig. An SFA rig only needs to accommodate one shorter auger section at a time. This reduces the working height and allows more compact machinery to be used. The choice can therefore be summarised as:

CFA piling: generally preferred where there is sufficient space, access and headroom and a high installation output is required
SFA piling: generally preferred where access, headroom, rig weight or site logistics prevent CFA equipment from operating

This does not mean that one method is inherently better than the other. Each provides advantages under different project conditions.

Access and Headroom Requirements

Access and headroom are often the first practical considerations when comparing CFA and SFA piling.

CFA Access Requirements

A CFA project must provide sufficient access for:

The CFA piling rig
The rig mast and complete auger length
Concrete pumping equipment
Reinforcement deliveries and storage
Spoil handling and removal
Supporting plant and site personnel

CFA piling is therefore usually selected for open construction sites where the rig can travel, manoeuvre and operate without significant overhead restrictions.

SFA Access Requirements

SFA piling can be carried out using more compact and lightweight equipment. It may be considered where the site has:

Low headroom
Narrow access routes
Standard doorway openings
Internal working areas
Basement-level pile positions
Weak or low access bridges
Narrow country lanes
Overhead power lines or structural restrictions
Limited space for plant manoeuvring

On some projects, compact SFA equipment can also be craned into an otherwise inaccessible working area. Learn more about restricted access piling.

Which Method Is Faster?

CFA piling is generally faster than SFA piling because the complete pile is drilled and concreted in one continuous operation. There is no need to stop repeatedly to connect or remove individual auger sections. This can make CFA piling particularly efficient for projects involving:

Large numbers of piles
Commercial and industrial developments
Open sites with good access
Programmes where installation output is a major consideration

SFA installation usually takes longer because each auger section must be connected during drilling and disconnected during withdrawal. However, installation speed must be considered alongside mobilisation, access and site preparation. A faster CFA method provides little benefit where the CFA rig cannot safely or practically reach the pile positions.

Does SFA Piling Mean a Lower-Capacity Pile?

Using a smaller SFA rig does not automatically mean that the completed pile will have a low structural capacity. SFA piles can be designed to support considerable compressive, tensile and shear loads. The capacity will depend on:

The pile diameter
The pile depth
The ground conditions
The reinforcement design
The structural loading
The capabilities of the selected piling rig

Smaller rigs are generally used for the lower range of pile diameters, while larger-diameter or deeper SFA piles require more powerful equipment. The pile system should therefore be designed around the project requirements rather than assuming CFA is always needed for substantial loads.

How Do Ground Conditions Affect the Choice?

Both CFA and SFA piling can be used in a wide range of soils, but the ground investigation findings remain essential when selecting the installation method. The assessment should consider:

The soil type, strength and consistency
The depth of suitable bearing strata
Made ground or variable fill
The level of groundwater
The stability of the pile bore
The presence of buried concrete, cobbles or boulders
The risk of encountering rock or other obstructions

CFA piles use a hollow-stem installation process, with concrete pumped from the base of the pile upwards as the auger is withdrawn. SFA installation can use either hollow-stem or solid-stem augers. The solid-stem method is limited to unsaturated, self-supporting soils where the bore can remain stable after the augers have been removed. Where the ground contains substantial obstructions, dense overburden or rock, neither CFA nor conventional SFA piling may be the most appropriate solution. A specialist method such as overburden drill and case piling may be required. Read more about why site investigation is important for pile design.

Noise and Vibration

CFA and SFA piles are both bored rather than impact-driven into the ground. Their installation creates little noise and is almost vibrationless compared with many driven piling systems. This can make either method suitable for work near:

Existing buildings
Occupied commercial premises
Railways
Substations
Utilities and buried services
Other sensitive structures or infrastructure

The smaller equipment available for SFA piling can provide an additional practical advantage where the site is particularly confined or where reducing the size and weight of plant is important.

CFA vs SFA for Commercial Projects

CFA piling is commonly considered for open commercial developments where a relatively large number of piles must be installed efficiently. Typical considerations include:

Sufficient access for larger equipment
Unrestricted working height
A suitable working platform
High pile quantities
Programme and productivity requirements
Space for concrete deliveries, reinforcement and spoil handling

SFA piling may be more appropriate for commercial projects involving:

Existing operational buildings
Internal structural alterations
Plant or machinery bases
Mezzanine foundations
Basements
Sites close to sensitive infrastructure
Extensions with restricted access or headroom

Visit our Commercial Piling page for more information about the available methods.

Can CFA and SFA Piles Form Retaining Walls?

Both CFA and SFA piling can be used to install contiguous bored pile retaining walls. A contiguous bored pile wall consists of a row of closely spaced reinforced concrete piles, normally connected at the top by a reinforced concrete capping beam. The selection between CFA and SFA will depend largely on:

Available access
Working headroom
Pile diameter and depth
Required installation output
Site layout
Ground conditions

CFA may be selected for larger open sites, while SFA can provide a solution where the retaining wall must be installed inside a building or beneath a headroom restriction. Learn more in our guide: What Is a Contiguous Bored Pile Wall?

Working Platform and Site Preparation

Both CFA and SFA equipment require a safe and stable operating area. The working-area assessment should consider:

The weight and dimensions of the selected rig
Track dimensions and bearing pressures
The strength and consistency of the underlying ground
Concrete-pump and delivery access
Reinforcement storage
Spoil handling and removal
Nearby excavations, services and structures
Drainage and changing weather conditions

A larger CFA rig will generally require a more substantial working area than compact SFA equipment. However, the use of a smaller rig does not remove the requirement for the ground to safely support the equipment. Read our guide to working platforms for piling rigs.

Which Method Is More Cost-Effective?

Neither CFA nor SFA piling is automatically the lowest-cost option for every project. CFA piling can offer programme and productivity savings where a high number of piles can be installed from an open and accessible working platform. SFA piling can avoid the practical cost and disruption associated with trying to accommodate a large CFA rig on a confined site. The total cost may be affected by:

The number of piles
Pile diameter and depth
Structural loading
Ground conditions
Rig mobilisation
Access and headroom restrictions
Working-platform requirements
Concrete and reinforcement quantities
Spoil handling and disposal
The required installation programme
Associated ground beams, pile caps or retaining structures

On a large open site, the faster CFA installation process may provide the more efficient solution. On a smaller or restricted project, mobilising a compact SFA rig may be more practical and economical. For further information, read our guide to CFA piling costs in the UK.

When Is CFA Piling Usually the Better Choice?

CFA piling may be the preferred solution where:

The site is open and unrestricted
There is sufficient vertical headroom
The access route can accommodate a larger rig
A relatively large number of piles is required
High installation output is important
The ground conditions suit the CFA method
Low-noise and low-vibration installation is required

It is commonly used for larger residential developments, commercial buildings, industrial projects and retaining-wall schemes.

When Is SFA Piling Usually the Better Choice?

SFA piling may be the preferred solution where:

Headroom is restricted
Piling must be completed inside an existing building
The site can only be reached through a narrow opening
A larger CFA rig cannot travel safely to the working area
The equipment must be craned into position
The project is beneath a bridge, roof, floor or overhead service
A smaller number of bored piles is required
Mobilising a larger CFA rig would not be practical
Work is close to sensitive infrastructure

Dawson Foundation Engineering has used SFA equipment to install 300mm diameter piles to depths of 10 metres in headroom as low as 3 metres. View the project: Restricted Headroom SFA Piling Works in Wilmslow.

Frequently Asked Questions

Are CFA and SFA piles the same?

No. They are both bored, cast-in-place piles, but CFA uses one continuous auger while SFA uses shorter auger sections that are progressively connected and removed.

Which method is faster?

CFA piling is normally faster because each pile is drilled and concreted in one continuous operation. SFA installation takes longer because the individual auger sections must be connected and removed.

Which method is suitable for restricted headroom?

SFA piling is normally the more appropriate option where working height is restricted. Its shorter auger sections can be installed using compact rigs inside buildings and beneath overhead structures.

Is SFA piling only used for small loads?

No. SFA piles can support substantial compressive, tensile and shear loads. Capacity depends on the pile diameter, depth, reinforcement and ground conditions rather than the name of the method alone.

Do CFA and SFA piles cause vibration?

Both are bored piling methods that create little noise and are almost vibrationless compared with many driven systems.

Can CFA and SFA piling be used for retaining walls?

Yes. Both methods can install closely spaced piles to form contiguous bored pile retaining walls. The choice will depend on access, headroom, pile requirements and site conditions.

Which method is cheaper?

The most cost-effective method depends on pile quantities, ground conditions, access, rig mobilisation, working-platform requirements and the project programme. CFA can provide high productivity on open sites, while SFA can be more practical for smaller or constrained projects.

Choosing Between CFA and SFA Piling

The decision between CFA and SFA piling should be based on the complete project requirements rather than one factor in isolation. Dawson Foundation Engineering will consider:

Ground investigation information
Structural loads
Pile diameter and depth
Access dimensions
Available headroom
Rig and working-platform requirements
Noise and vibration constraints
Pile quantities and programme
Concrete, reinforcement and spoil logistics
Nearby buildings and infrastructure

Where the site is open and a high-output installation is required, CFA may provide the most efficient solution. Where access or headroom prevents a full-height CFA rig from operating, SFA can provide a versatile alternative. To discuss your project, call 0333 224 5196 or contact our team to arrange a free site visit and no-obligation quotation.

FOUNDATION ENGINEERING

CFA vs. SFA Piling: What’s the Difference?