Piling Explained…

What is ‘CFA piling?’ CFA is an abbreviation of ‘Continuous Flight Auger’, this method of piling involves drilling the pile, and upon extraction pumping concrete under pressure, meaning there is never an ‘open bore’. The specified reinforcement cage can then be installed into the concrete. No hammer is utilised with this method, so it produces little noise and next to no vibration, appeasing many planning conditions.

What is ‘rotary bored piling?’ Rotary bored piling is similar to CFA, however the auger is removed in its entirety, and casings or drilling fluid are utilised for ground support. The cage is then installed prior to pouring the concrete. This method usually involves larger diameter piles and has a slower production rate, due to there being a greater number of processes.

What productions can be achieved with CFA piling? There are many factors that can affect production rate, the main ones being, depth, diameter, strata, obstructions, foundation layout and concrete availability. On the smaller diameters such as 300-400mm with good ground conditions and concrete availability, 300 linear metres plus per day should be achievable.

What are the limitations of a CFA pile? This will depend on the rig being utilised, however at GM Piling we can install diameters from 300mm up to 1200mm. Achieving depths up to 28.5m, CFA piling is suitable for a multitude of different projects across many sectors.

When should CFA piling be used? CFA piling provides a low noise and low vibration foundation solution, which is attractive to many planning committees as well as utility companies and Network Rail. It has the benefit of being quick to install and can be utilised 1100mm from any existing structure. This solution can be installed in the form of a load bearing pile, or a retaining wall into most strata for many different projects within many different sectors.

The piling dictionary

Attendances – A list of items to be provided by our clients to complete the piling works.
For example: full time 13t excavator and driver, water supply, washout skip, background lighting, etc.

Auger – A large drilling tool with a hollow stem, encompassed by helical flights that are used
to drill into the ground, and create the bore for the pile.

Cased Piling – A steel sleeve is oscillated into the ground, the pile is drilled and then formed through the centre of the casing. The casing is utilised to control pile position and verticality,
or as a method of supporting unstable soil types, and can be permanent or temporary. The pile is then installed as per ‘What is CFA piling’. This method can enable all piling to be done from one level, where the cages can be hung and the concrete left low, resulting in substantial cost and carbon savings.

CFA Banksman – Duties include monitoring the pile locations, depths and ensuring that the specified reinforcement is installed, whilst maintaining a tally of all piles completed on the project to date.

Concrete Cube Testing – A sample of concrete is taken, formed in a 100mm cube shaped mould and left to cure. The cube is then crushed to make sure it conforms to the specified concrete strength.

Concrete Pump – The plant used to move liquid concrete from an agitator or holding drum to the rig, where it is transported through the hollow stem of the auger, and into the bore to form the pile.

Contiguous (Contig) Wall – A wall consisting of a series of piles, typically installed with a spacing of 150-300mm. This type of wall is normally utilised in a cohesive soil type.

Dead Load – A permanent load applied to a pile and is not subject to regular change,
for example the weight of the building itself.

Driven Piling – A preformed pile, that is either hammered, vibrated or pushed into the ground. This is both noisy and causes vibrations, so tends to be used in unbuilt up areas.

Dynamic Load Testing – Testing by dropping a load on to the top of the pile. The speed that the load is dropped, and the strain caused by this process is recorded. This method of testing is not generally practised with Continuous Flight Auger piling.

End Bearing – Where the load of a pile is transferred through the base of the pile into the ground.

Eurocode 7 – The standard design approach for geotechnical engineering, which is recognised across the European Union (and the UK).

Geotechnical Engineering – A discipline of civil engineering which focusses on the behaviour of geological materials. GMP have a team of in-house design engineers who undertake the geotechnical assessment of site ground conditions, to ensure a stable foundation is achieved.

Groundwater – Water that is found within the soils.

Holding Drum – Also referred to as an agitator. This plant is utilised to store concrete,
and keep it live in the short term, to minimise standing time and facilitate a consistent
supply in busy areas.

Horizontal Load – A force that is applied against a structure from a lateral direction
such as wind.

Integrity Testing – The pile is struck with a hammer, generating a ‘compression wave’.
This travels down the pile and informs the tester of any issues with the pile, like cracks
and voids etc.

Kingpost Wall – A series of piles installed at approximately three metre intervals, with a steel ‘H’ beam inserted into the concrete pile. Concrete sections are then slid down the grooves of the ‘H’ beam to retain the ground behind.

Live Load – The imposed load transferred to a superstructure. The loads are transferred into the substructure through the structural skeleton of the building. These loads are dependent on the use of the building, but typically include the weight of furniture, people, machinery etc.

Pile Reinforcement – The steel bars and rings that are tied or welded together, to form a cage and strengthen the pile, as per the specified loadings.

Piling Supervisor – Whose duties are to supervise the crew and maintain communication between the Sub-Contractor, Main Contractor and other relevant parties.

Plate Load Testing – A jack is installed between an excavator and the ground. It is extended
to measure the amount of load or force that the ground can withstand.

Pump Operative – The person who operates and maintains the concrete pump and holding drum, controlling the flow of concrete from the drum to the pile itself.

Rig – The plant that is used to drill and form the pile.

Rig Operator – The driver of the rig, who monitors the rig telemetry and records the pile depths.

Secant Wall – Typically used for basements, and withholding sands and gravels, a secant wall, is a series of piles that overlap or interlock forming a barrier to help retain groundwater.

Shaft Friction – The interaction between the pile shaft and the ground. Shaft friction serves
an important purpose when limiting foundation settlement.

Sheet Piling – Interlocking steel sheets, that are driven into the ground to retain ground and form waterproof barriers. This method of ground retention can be utilised for both the temporary or permanent state.

Static Load Testing – A test that pushes against the pile, to generate 100%, 150% and or 200% of the anticipated loadings that the pile will be expected to withstand when the building is completed.

Strata – The layers of the varying soil types that make up the ground.

Vibration Monitoring – Recording the vibrations caused at various distances from the source.