Secant Piling

Principles Of Construction

  • Often known as "Benoto" piling, which is a type of trade name.  Usually replaced by diaphragm walling methods.
  • Essentially typical bored piles, or down-the hold type bored piles, are constructed with a spacing slightly smaller than the chosen diameter of the piles.  Once a suitable length of piling has been completed, the "holes" are filled with a similar bored pile which intersects and "bites" into the two previously constructed piles.
  • Usuall these piles are strengthened with a steel "H" pile, rather than the typical reinforcement cages used in standard bored piling.

As-Built Examples

  • Large diameter circular secant pile cofferdam.
  • Structure consisting of 1,200 mm diameter secant piles to a depth of 20 which then stepped into 900 mm contiguous piles for a further 20 m depth.  Each pile was probed to 10 m depth in advance.  A total of 255 number piles were constructed.
  • The "cofferdam" had a 1.4 m deep concrete base slab with a concrete lining to the walls.
  • An intermediate concrete roof slab was placed to form an underground box structure.
  • Overall construction time  12 weeks (Heathrow Express).

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