Secant Pile Wall

A piled secant wall is formed by installing interlocking vertical bored piles which form a solid barrier free of gaps, capable of retaining the ground without loss of fines and limiting the passage of water to minor seepage. 

Construction Sequence

1. Form a 'guidewall' with predetermined spacing to accurately position the secant pile prior to drilling operations.
2. Drill and cast a series of female (unreinforced) piles formed in soft or firm concrete.
3. Drill the corresponding series of male piles through the previously cast female piles utilising the casing or heavy duty augers to cut the required secant male pile to design depth. 
male piles through the previously cast female piles with the required design intersect utilising the casing to cut the required secant
4. Cast the male piles with full reinforcement cage (and withdraw the casing, if used) to allow the concrete in the male piles to flow and bond with the existing concrete of the previously cast female piles.
5. Install a capping beam to tie piles together; ensuring the wall acts as a monolithic structure.
6. Excavate soil in from in front of the wall to allow the secant wall to retain the soil behind.
7. Install temporary and/or permanent propping where design requires.  

Fields of application

(Similar to Contiguous Piled Walls, with the added benefit of temporary water and fines retention)  

  •  New basement structures, especially in urban areas.
  • Additional support for highways subject to embankment slippage (slope stability).
  • Implemented as permanent earth retaining structures along road and railway lines in excavations.
  • Bridge abutments carrying horizontal.
  • Embankment cuttings

Secant walls are ideal for new basement construction, particularly in built up areas where noise and vibration would be a problem, and where soil and water retention are required.

Environmental Impact

Secant walls can be installed without the noise and vibration associated with driven sheet piles enabling high capacity retaining structures to be constructed adjacent to existing buildings which may be sensitive to noise and vibration. 

Technical Specifications

  • Temporary or permanent earth-retaining structure: restricting movements of the soil on the retained side.
  • Suitable for temporary retaining of water or groundwater ingress and able to retain fines (unlike a contiguous wall) 
  • Due to rotary drilling techniques, this system is applicable in a wide range of soil conditions: granular soils, most cohesive soils, soft layers of rock. 
  • Unsuitable in hard clay and hard rocks
  • Piles are usually constructed with a nominal overlap between the piles to ensure 'secanting' remains to depth or to impermeable clay layer; dependent on site requirements.
  • The piles are designed to carry lateral bending forces, and are normally tied together at the top with a capping beam to ensure they act monolithically. 
  • Depth of excavation is limited by the length of the piles cage reinforcement introduced in to the piles (maximum 18.0m for CFA and may become more economical for diaphragm wall systems at depth).
  • Apart from retaining walls to resist lateral earth pressure supplementary strutting systems are also required.
  • Ability to support an axial loading (point load and/or line load distributed through capping beam). 

Related projects for this technique

Franki Foundations UK

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Martello Piling

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