What Are Secant Pile Walls?
Table of Contents
- About Secant Pile Walls
- What Are Secant Pile Walls Used For?
- How Are Secant Pile Walls Constructed?
- What Is the Difference Between Cantilever Pile Walls and Secant Pile Walls?
- Advantages of Secant Pile Walls
Last updated
17 February 2025
About Secant Pile Walls
Secant pile walls are formed by constructing intersecting reinforced concrete piles. The secant piles are reinforced with either steel rebar or steel beams and are constructed by augering. Primary piles are installed first with secondary piles constructed in between primary piles once the latter gain sufficient strength. [1]
Pile overlap is typically in the order of 8cm. They are constructed when resistance to groundwater is required using the CFA technique or the cased CFA technology.
What Are Secant Pile Walls Used For?
Secant pile walls are usually installed as retaining structures and support systems for deep foundations, retaining elements and at the same time load-bearing walls and deep foundations for engineering constructions (e.g. walls and foundations of underground storeys, stand-alone and framed bridgeheads, etc.).
How Are Secant Pile Walls Constructed?
Secant pile walls can be constructed using the CFA or the Cased CFA technology, consisting of reinforced piles with the gaps between them filled with:
- Columns made of low-strength material of 1-3 MPa (concrete or mortar, usually with bentonite), spaced approx. 620-670mm for a drilling diameter of 470-500mm. This solution ensures resistance to groundwater (temporary support), but does not guarantee permanent water resistance. In order to ensure permanent water resistance, additional liners or sealing agents are required.
- Columns having a compressive strength of 10-20 MPa and prolonged binding time (56-day strength instead of 28-day strength), spaced 700-750mm for a drilling diameter of 470-500mm. This solution ensures long-term water resistance, provided that a minimum overlap of 25mm is provided.
- Full-strength concrete piles with prolonged binding time, spaced approx. 400mm for a drilling diameter of 500mm. This solution also ensures long-term water resistance and is widely used as a support system for deep excavations with a pile wall constructed on a circular plane, since waling beams and/or struts are not required.
This video demonstrates the secant piling method, which involves the installation of a secant pile wall & Vor der Wand:
What Are Male and Female Piles?
The primary piles/columns cast first are called female or soft. The reinforced load-bearing piles are drilled to intersect the female piles/columns and are called male or hard.
What Is the Difference Between Cantilever Pile Walls and Secant Pile Walls?
Cantilever pile walls can be used for protecting land faults up to 5m high or, if using anchors or struts, up to 20m high. Secant pile walls allow for protecting land faults up to 5-6m or, if using anchors or struts, up to 25m high. The standard rake of the installed pile wall does not exceed 1:75, however, under special monitoring, the rake can be reduced to 1:125 and, in some cases, even to 1:200 for secant walls made of hard piles and installed using the CCFA technology.
Advantages of Secant Pile Walls
The main advantages of secant pile walls are:
- Provide increased wall stiffness compared to sheet piles
- Can be installed on difficult ground (cobbles/boulders)
- Vibration-free and low noise construction
- Greater retained heights than piling alternatives
- Water-resistant
- Can bear axial loads
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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