Construction methods · Driven piles

PHC spun concrete piles

Hollow prestressed concrete piles spun in a factory at 80 MPa or more, 350-1,200 mm in diameter, delivered in 10-15 m lengths and jointed with welded end plates. The economical pile of Korea, Japan, China and Southeast Asia wherever a dense sand or gravel layer sits within 10-40 m.

How bridges get built · Driven piles · PHC spun concrete piles

Also called: prestressed high-strength concrete pile, spun pile, PHC pile

rockhydraulic hammerleaderwelded joint platedriven to set in dense sand or gravelhollow spun pile350-1,200 mm, 80 MPaPHC spun concrete piles
Concept diagram (TheBridgeEng)

How it is done

  1. Set out and pitch the first segment in the leader of a piling rig; drive with a hydraulic hammer using a cushion to protect the head.
  2. Weld the next segment on at the joint plate with a full-penetration weld; continue driving to the design set or to a dense layer confirmed by the blow count.
  3. Cut the head to level, break down to expose the strands or insert a cage in the hollow for the cap connection.
  4. Restrike a sample of piles after a day or more and run PDA tests to confirm capacity.

Where it fits

  • Alluvial and coastal sites with a bearing layer of dense sand or gravel; viaduct approaches, low piers, wetland viaducts on trestles.
  • Loads of 1-4 MN per pile; groups of 4-20 under a cap.

Where it does not

  • Boulders, cobbles and shallow rock: the pile refuses, cracks or breaks (the game's boulder event).
  • Very stiff clay over the full length: hard driving damages the joints.
  • Urban sites with noise and vibration limits.

Plant, pace and money

PlantPiling rig with a 7-15 t hydraulic hammer, service crane, welding set; barge-mounted rigs for shallow water.
Productivity6-15 piles of 20-30 m per rig per shift.
CostUSD 60-140 per metre installed for 600 mm; the cheapest deep foundation where it works.

Risks and controls

What goes wrong

  • Tension cracking during easy driving in soft clay, joint failure, pile running off line, heave of neighbouring piles in clay.

Quality assurance

Driving records (blows per 250 mm), PDA on 5-10 % of piles, integrity tests after driving, verticality within 1:75.

Examples

Most Korean expressway viaducts on alluvium; the reference optimiser picks PHC where a dense layer is reachable.

Related methods

Driving control: sets, refusal, restrike and splicingImpact hammers: hydraulic, diesel and dropPrestressed concrete square pilesSteel pipe piles (open- and closed-ended)

Further reading

KS F 4306 · JIS A 5373 · PCI Bridge Design Manual

Prestressed concrete square piles →