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Concrete for female secant piles

The  low  strength  concrete for the “female” piles  has  a  number  of  functions  but first  and  foremost  it needs  to  retain  the  ground  and  groundwater  from  passing  between  the  reinforced  concrete “male” piles. However, to achieve this and facilitate construction the concrete requires the following properties:

 

1. Sufficient  strength  to  support and distribute the earth pressures to the “male” piles. In reality these piles are spanning less than a pile diameter and the forces are distributed by arching  with  the  material  in  compression. 

 

2.Low permeability to minimise the seepage of groundwater through either the piles or secant wall as a whole.

 

3.Low  early  strength  gain  to facilitate the boring of the “male” piles. The difference in strength between the adjacent “female” piles is likely to affect the drilling tolerances of the male piles and thus verticality and overlap achieved.

 

4.Suitable for pumping without segregation and maintaining stability during and after the placing.

 

5.Suitably  durable for the intended life of the material. The “female” pile is typically unreinforced  and  effectively  temporary  if  a  permanent  lining  wall  is  constructed  on  the inside face of the piles. For this reason durability is not normally a concern and a design chemical class does not need to be specified.

 

The relatively weak concrete in the female piles can lead to long term durability problems and the secant pile wall can only be considered to be water resistant in the short term.

Secant pile wall
 
Acknowledgement: The Concrete Society
 

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Contiguous and secant piled walls