Secant Piling
DAWSON-WAM is a leading specialist in the design and installation of secant piled retaining walls for basements and deep excavations. Secant piles are formed by a sequence of interlocking bored concrete piles, creating a strong, continuous retaining structure. This method is particularly effective in poor ground conditions and sites with a high water table, where alternative systems may not be suitable.
What is a Secant Piled Wall?
A secant piled wall is a retaining wall formed by a series of overlapping concrete piles. The wall is constructed by first installing primary (typically unreinforced) piles, followed by secondary reinforced piles that are drilled between and cut into the primary piles.
The reinforced secondary piles provide the structural strength of the secant wall, resisting the earth and water pressures acting on the excavation. The primary piles act as gap fillers between the structural piles.
The overlap between adjacent piles creates a continuous wall with excellent structural strength and groundwater control. Secant piled walls are commonly used for deep excavations, basements, shafts, railway infrastructure, highways, and other projects where ground retention and water exclusion are required.
Market-Leading Cased CFA Capability
As the largest Cased CFA (Continuous Flight Auger) piling specialist in the UK and Ireland, DAWSON-WAM delivers secant walls with unmatched precision and reliability. Our Cased CFA system provides:
- The speed of CFA, combined with the precision and capability of rotary techniques
- Flighting risk elimination for improved bore stability
- The ability to bore through obstructions, mass concrete, and medium-strong rock
- Enhanced verticality and accuracy for optimised pile spacing and reduced programme time
This system is particularly well-suited for secant wall construction in sensitive environments, offering low-noise, vibration-free installation ideal for city centres and constrained sites.
Secant Wall Options with Our Cased CFA System
We offer multiple secant wall configurations to suit different project needs:
- HARD/HARD Secant Walls – Both primary and secondary piles are constructed from structural-grade reinforced concrete
- HARD/FIRM & HARD/SOFT Secant Walls – Primary piles use a lower-grade concrete while secondary piles are structural grade
While all types have their applications, DAWSON-WAM specialises in HARD/HARD secant walls, which provide significant advantages:
- Maximum strength and stiffness – All piles are structural concrete, and both primary and secondary piles can be reinforced
- Superior water retention – Enhanced bond between piles improves watertight performance
- Efficient load distribution – Axial loads can be spread through the piles, reducing capping beam requirements
- Optimised pile spacing – Greater vertical accuracy and concrete strength allow for fewer piles, lowering cost and installation time
Overcoming Ground Challenges & Obstructions
Using our Cased CFA (Continuous Flight Auger) piling system, we can negate flighting risk and maintain precise bore stability, even in variable or difficult ground conditions. Our equipment is capable of boring through:
- Natural obstructions
- Mass concrete and brick structures
- Medium strong rock (<50MPa)
This capability allows us to maintain programme certainty and minimise the risk of delays when unforeseen ground conditions are encountered.
Low-Noise, Vibration-Free Installation
Our relatively silent and vibration-free piling techniques make secant piled walls ideal for use near existing buildings, roads, and sensitive structures. For tight urban environments, we can also deliver virtually zero-tolerance secant pile installation, maximising usable space without compromising safety or quality.
Applications in Basements & Underground Construction
Secant walls can form a continuous watertight barrier, making them an excellent choice for basement construction and underground car parks. DAWSON-WAM offers complete basement and foundation packages, including:
- Piling design and setting out
- Circumference piling
- Capping beams
- Bulk excavation
- Temporary load anchoring and propping
- Foundation piling, pile caps, and reinforced concrete works
- Structural steel installation from basement to ground level
We also provide full pile testing, along with vibration and noise monitoring, ensuring compliance with industry standards and local environmental requirements.
What is a Guide Wall?
A guide wall is a temporary structure installed before piling works begin. It provides alignment and positional control for piling rigs, helping ensure piles are installed accurately and to the required tolerances. DAWSON-WAM always use guidewalls on secant and contiguous piled walls to ensure precision is achieved.
DAWSON-WAM Sustainable Guide Wall
DAWSON-WAM’s Sustainable Guide Wall is an innovative reusable alternative to traditional polystyrene guidewall formers. Designed to deliver the same level of accuracy and performance, the system significantly reduces plastic waste and embodied carbon.
By replacing polystyrene with a biodegradable solution, projects benefit from faster installation, improved sustainability and a reduced environmental footprint without compromising quality or safety.
Get in touch with our team
Featured Projects
Visit our Projects Section to see examples of our secant piled retaining wall and basement construction works, or contact us to discuss your project-specific requirements.
