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Secant Pile Walls

Secant pile walls are formed by constructing intersecting circular reinforced concrete piles. They may be constructed either by using segmental temporary casing and conventional heavy duty rotary drilling tools or by continuous flight auger (CFA) techniques. A reinforced concrete guidewall is constructed at piling platform level to aid positional and verticality tolerances.

Primary (or Female) piles are installed first. Once the Primary piles have gained sufficient strength, Secondary (Male) piles are constructed in between them and cutting into the Primary piles. Pile overlap (cut) typically ranges from 100mm to 250mm. Primary piles are usually unreinforced. Secondary piles are usually reinforced with full length steel reinforcement cages or, less commonly, with steel sections. After construction, piles are broken down and usually incorporated into a reinforced concrete capping beam.

The main advantages of secant pile walls are:

  • Plan footprint flexibility
  • Increased wall stiffness
  • Load bearing capacity
  • Can be installed in difficult ground
  • Grade 1 Basement water-tightness