What Are Contiguous Pile Walls?
Table of Contents
- About Contiguous Pile Walls
- Common Uses of Contiguous Pile Walls
- How Are Contiguous Pile Walls Constructed?
- Advantages of Contiguous Pile Walls
Last updated
17 February 2025
About Contiguous Pile Walls
A contiguous pile wall, also known as contig piles or contig wall, is a retaining wall system, mainly constructed using the CFA technology. It consists of adjacent reinforced piles, which can include soft reinforcement (such as a cage) or firm reinforcement (such as a steel section). [1]
Contiguous piled walls are utilised when groundwater ingress is not an issue. This method is suitable in a variety of soils where groundwater lies below the maximum excavation depth. The dimension of the gap between the piles typically ranges between 50 and 150mm. A permanent wall can be created, taking the form of a structural concrete facing wall tied to the piles or sprayed concrete.
Contiguous piling, or contig piling, is the ideal choice for earth retention systems in crowded urban areas, where alternative retaining methods would not be applicable and where development space is limited.
Common Uses of Contiguous Pile Walls
Contiguous pile walls are employed across a range of engineering projects, including:
- Basement Construction – Providing lateral support during excavation to prevent ground movement and structural failure.
- Underground Car Parks – Ensuring structural integrity for large-scale underground parking facilities.
- Rail and Highway Infrastructure – Retaining earth in cuttings and embankments to maintain stability.
- Slope Stabilisation – Preventing soil erosion and landslides in areas with steep terrain.
- Flood Defenses – Supporting water management structures to mitigate flooding risks.
- Urban Excavations – Essential for deep excavations in cities with restricted space for alternative retaining solutions.
How Are Contiguous Pile Walls Constructed?
Contig walls are mainly installed using suitable piling techniques. The construction process generally goes as follows:
- Site Investigation & Design – A thorough geotechnical survey is conducted to assess ground conditions. The appropriate pile diameter, spacing, and depth are determined based on structural and environmental factors.
- Pile Installation – Using drilling rigs, retaining wall posts are installed in a predetermined sequence. Piles are typically reinforced with steel cages for additional strength and durability.
- Excavation & Ground Support – As excavation progresses, additional temporary support measures, such as props or anchors, may be installed. In certain cases, shotcrete is applied to exposed sections for extra reinforcement.
- Finishing Works – Depending on project requirements, the wall can be finished with a facing material, waterproofing, or additional structural elements. Drainage measures, such as weep holes, may be integrated to manage water pressure effectively.
Advantages of Contiguous Pile Walls
The main advantages of contiguous walls are:
- Easier to build in load variations, with no requirement for a guidewall
- It’s a cost-effective bored pile solution, compared to Diaphragm walls
- They can be used for more flexible geometry than a diaphragm wall
- Provides load-bearing capacity
- Can be installed in difficult ground conditions
- Ideal for metropolitan cities (Urbanisation makes the cost of land high and so it is increasingly common to go deeper into the ground)
- CFA piles are considered more economical than diaphragm walls in small to medium-scale excavations due to the reduction in cost and time of site operations
- Suitable in crowded urban areas, where traditional retaining methods would otherwise encroach the adjoining properties
- The presence of footings of adjacent buildings and underground utilities on a site make contiguous walls the ideal choice for supporting an excavation
- Have a faster speed of installation when compared with secant piled walls
Written by Aarsleff UK
17 February 2025
Aarsleff Ground Engineering is a leading sheet piling supplier and contractor. We specialise in designing and delivering sheet piling solutions across the UK.
Reviewed by John Storry, Retaining Walls Director
17 February 2025
John Storry is our Operations Director for Specialist Retaining Walls, having amassed a wealth of experience and knowledge in the construction market. John has held senior positions within several companies already well-established in the sheet piling sector and has been with Aarsleff since 2016. John operates on a practical, estimating, commercial and development level to capitalise and gain the traction needed to take Aarsleff’s sheet piling arm of the business to the next level.
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