what is a secant anchored pile wall?

The anchored secant pile wall consists of primary (soft piles) and secondary (Hard piles) bored piles connected by a capping beam on the top. This secant pile wall is a permanent retaining wall system for ground retention prior to excavation.

The primary bored piles were constructed of plain concrete, while the secondary bored piles were constructed of reinforced concrete. The reinforced piles are then installed and the reinforcement can be either cage, I-beams, or H-beams. The secant pile walls Formed by intersecting reinforced and unreinforced concrete piles.

According to the soil condition and site requirements, a secant pile wall design will be carried out. This wall needs to be tied at certain intervals to ensure the stability of that wall against the combined earth and water pressures. This is achieved by providing back ties to the secant pile wall using ground anchoring. A prestressed grouted ground anchor will be installed in soil or rock that is used to transmit applied tensile loads into the ground.

Main components of a ground anchor

Bond length: Transfers the forces to the load-bearing soil via skin friction between grout and soil interface.
Free length/Unbonded length: This allows for elongation of the strands during tensioning and transmission of forces to the bond length.
Anchor head: The mechanical link between the anchor body and the structure.

Ground Anchor design

  1. Ground Anchor specification and allowable forces will be reviewed to check the structural capacity of anchors or anchor strands.
  2. Design free length of ground anchor will be calculated.
  3. Design bonded length of the ground anchor will be calculated.
  4. Ground Anchor jacking force calculation will be done.

Finally, an analysis of progressive collapse mechanism check will be done. It is analyzed to check the consequence of loss of a single anchor in the secant pile wall, for whatever reason this should happen. In this case, two adjacent anchors have to be able to sustain an increased load, without leading to a collapse of the whole system.

Author Credit: Mohamed Vistash Civil Engineer MICE|Chartered Civil Engineer | ICE Mentor

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