Contiguous Piling & Pile Walls

Contiguous pile walls consist of piles set close to each other to retain soils and form a supporting structure. Contiguous piling is a cost effective technique which is widely used and ideally suited for construction projects in urban areas, especially on sites with dry, cohesive soil.

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We’re the trusted contiguous piled wall specialist in London and Sussex

We work on a range of domestic and commercial piling projects. Our professional and experienced team of piling contractors and civil engineers offer a range of piling services, including:

What is Contiguous Piling?

Contiguous piled walls consist of a continuous line of piles separated by a small space. We create the piles by using continuous flight augers or rotary augers to remove the soil and then fill the resulting cylindrical hole with concrete.

The size of the space between piles is determined by the nature and condition of the soil, and is typically between 50mm and 150mm. The space between piles allows each one to be drilled without disturbing the preceding pile. If needed the gaps are filled with grout to hold back loose, fine soil, or sealed to block off water seepage.

To aid the structural integrity of the piling, and to facilitate load-bearing, a capping beam can be laid across the tops of the piles. Ground anchors or props add further support for the piling if needed.

What are the differences between CFA and rotary piling?

CFA piling is generally a faster, smoother technique than rotary piling. However, CFA piles are limited to a smaller diameter with a lighter load-bearing capability. Rotary piles are larger and can support heavier loads, and rotary rigs are able to drill into harder rock than CFA rigs.

With a wealth of specialist piling experience behind us, we will advise on exactly the right type of piling for your project.

When do you need contiguous piles?

At Performance Foundations we use contiguous piling for various projects including:

  • Safe excavation of basements, especially in urban areas
  • Stabilisation of slopes and inclines
  • Rail and road cuttings
  • Underground tanks
  • Maintenance of ground of an adjoining property

Contiguous piles are used in a wide range of soil conditions including loose, granular soils, cohesive, clump-forming soils and soft layers of rock. The technique is less well-suited to hard clay and rocky ground.

What are the advantages of contiguous piling?

Contiguous pile walls are often used in built-up areas, or on projects close to neighbouring buildings, such as basement works and home extensions in cities and towns. The technique involves little vibration compared to pile driving, and it will not damage or destabilise buildings in close proximity. It also makes a lot less noise.

Contiguous piling is also very cost effective and quick to complete, especially in comparison to concrete retaining walls whether or not they are cast on site, or made from pre-cast sections. Only the drilled earth is removed as opposed to the major excavation needed for a retaining wall, and they do not require such large access areas. Contiguous piling is also much more flexible for sites involving many different shapes, not just large, straight sections.

What are the types of contiguous piling?

We use two construction methods for contiguous piled walls:

  • CFA (continuous flight auger) piling removes soil with an auger while at the same time concrete is pumped through the auger’s hollow centre.
  • Rotary piling removes soil with an auger, then a reinforcing structure is inserted followed by poured concrete.

Both methods are technically effective, and can be used when the available working area means that excavation must be vertical. They are a temporary or permanent means of retaining the sides of bulk excavations, even in water bearing strata, and use the same techniques as foundation bearing piles. In permanent installations, contiguous piles can be designed to bear horizontal as well as vertical loads.

CFA piling

In CFA (continuous flight auger) piling, the piles are drilled and filled with concrete in one continuous operation. As the auger screw lifts the soil out of the drilled hole, wet concrete is poured through the central core of the drill. A further technique is Cased CFA piling which uses a casing inserted into the drilled hole before filling with concrete. The casing adds strength and stability to the pile if required by ground conditions and load bearing requiring requirements. CFA piling and can be used in most types of ground including loose sandy soils, clay and softer rock.

Rotary piling

Rotary piling, or rotary bored piling, uses an auger to drill the piling hole. Rigs may include a range of auger drills and buckets for the removal of the excavated soil.  Steel casing is then inserted before filling with concrete. If the casing is temporary, it is removed and re-used.

How are contiguous piled walls made?

Our approach to contiguous piling projects features the following steps:

  • Specification defined for piling depth, diameter and number of piles
  • Decision made about using CFA or rotary piles
  • Piles excavated, piling cages installed if used
  • Concrete poured and given time to set
  • Capping beams to tie piles together and give piling structural strength
  • Put propping and supports in place (permanent or temporary) where required

Once finished, the site is ready for the next phase of project, including basement construction or above-ground building work.

This is one of the specialist services provided by Performance Foundations for construction projects in London, Surrey, Kent as well as Sussex and the rest of South East England. The expertise of our team and our specialist equipment and allow us to successfully complete projects on sites with restricted access due to low headroom, limited workspace and difficult ground conditions.

Contiguous pile walls for different ground conditions

With two different techniques available for contiguous piling, we have expertise ion working with soils of all kinds. For hard clay or rocky ground we will use our rotary piling rigs. For softer soils, we will use our CFA equipment. We can also construct contiguous piling on sloping sites where the piling needs to retain the ground.

Complete piling services

If contiguous piling is not the best solution for any site, we will use a different piling technique to meet the requirements and challenges of any construction project. Our expertise also covers bottom driven piling, piling walls and reinforced concrete retaining walls, as well as underpinning and ground beams and slabs.

We also have the equipment and know-how to work in restricted spaces with low headrooms and limited access. Our mini-piling rigs are designed to operate in small spaces, such as existing basements or narrow urban sites.

What is a contiguous piled wall?
Contiguous piling consists of a series of cylindrical piles with gaps of usually of 50mm to 150mm between them. The piles are made of concrete, with or without a casing for added strength.

What is an auger screw?
An auger screw is a flanged drill which penetrates the ground and lifts the soil up the screw on the flanges. The same principle is used in screw conveyors for industrial machinery.

What is a contiguous piling rig?
Piling machines are known as rigs. Contiguous piling rigs are based on an auger screw which drills down into the ground and removes soil to create a cylindrical cavity. Rigs may include buckets and conveyors to remove the soil from the immediate site.

What is a rotary piling rig?
A rotary piling rig is based on an auger screw and is suitable for drilling larger piles and working in hard ground and rock. Rotary piling will meet the challenges presented by almost any ground conditions.

What is a CFA rig?
A CFA (continuous flight auger) rig pumps in concrete through a central tube at the same time as it drills out soil with the auger screw. It is a highly efficient and cost effective piling technique for softer ground.

When is contiguous piling required?

Contiguous piling is the appropriate technique for multiple construction projects including:
• Basement extensions
• New basements
• Sloping sites
• Support and soil retention for neighbouring sites
• Cuttings for rail and road
• Below ground tanks and vessels


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