Construction methods · Cast-in-place concrete decks

Falsework on temporary piles (shallow water)

Cast-in-place on falsework carried by temporary steel piles driven into the riverbed, so the method survives 1-3 m of slow water outside the flood season. The classic construction of small river and canal bridges before precast girders took over.

How bridges get built · Cast-in-place concrete decks · Falsework on temporary piles (shallow water)

Also called: piled falsework, trestle falsework, falsework in water

How it is done

  1. Drive temporary steel pipe or H piles in bents under the falsework beams; brace them against current and debris.
  2. Set the falsework beams and soffit on the bents above the flood-season water level; the rest as for ground falsework.
  3. Strike and extract the piles before the wet season.

Where it fits

  • Slow rivers and canals up to about 3 m deep, spans 20-45 m, dry-season programmes.

Where it does not

  • Water beyond 3-5 m, velocities over 2 m/s, navigable routes, flood seasons.

Plant, pace and money

PlantPiling rig or barge with vibro-hammer, temporary piles, falsework, formwork.
ProductivitySlower than ground falsework: allow 45-60 days per span.
CostAdds USD 100-250 per m2 for the piles and bracing.

Risks and controls

What goes wrong

  • Flood taking the falsework, debris loading, scour of the temporary piles, boat impact.

Quality assurance

Flood watch and evacuation plan, pile driving records, bracing inspection.

Examples

Small river bridges in Korea, Japan and Europe until the 1980s; still used for canals and irrigation crossings.

In the bridge game

What Bridge Master applies when you pick it

Deck types: RC slab, Voided slab, RC T-beam, RC box, PSC box (cast in place), Rigid frame, Concrete arch, PSC box, balanced cantilever, Extradosed, Network tied arch. Spans 20-45 m, up to 60 m.

  • +25: Shallow, slow water: piled falsework is the cheap answer.
  • -40: Too deep for piled falsework.
  • -30: Fast water loads the temporary piles and debris piles up.
  • -15: Only in the dry season; the falsework must be out before the floods.
  • -30: Blocks the navigation route.
  • not allowed: Piled falsework in 5 m+ of water is not a temporary works design, it is a bridge.

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Related methods

Full staging method (ground falsework)Temporary trestles and access bridgesLaunching girder (beam launcher) for precast girders

Further reading

BS 5975 · Japan Road Association temporary works

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