Construction methods · Caissons and marine foundations

Temporary trestles and access bridges

A steel-piled bridge for cranes and trucks built out over shallow water alongside the alignment, so the permanent piers can be built with land plant. It costs a bridge of its own but removes barges, tides and weather from the pier works.

How bridges get built · Caissons and marine foundations · Temporary trestles and access bridges

Also called: work trestle, temporary access bridge, piled trestle

Concept diagram (TheBridgeEng)

How it is done

Drive steel pipe piles in bents at 10-15 m from the trestle's own head; add capping beams and main girders, then a deck of precast panels or steel plates.
Extend bent by bent; add working platforms at each pier.
Remove in reverse after the deck is built, or leave piles cut below the bed where permitted.

Where it fits

Rivers, wetlands, estuaries and coasts with water to about 5-6 m, viaducts with many piers, sites where barges cannot operate at low tide.

Where it does not

Deep water, navigable channels, flood seasons that would carry the trestle away, environmentally protected wetlands (use top-down instead).

Plant, pace and money

PlantCrawler crane with vibro-hammer working from the trestle head, pipe piles, steel girders, deck panels.

Productivity20-40 m of trestle per day.

CostUSD 8,000-20,000 per metre; the game charges this as the access line.

Risks and controls

What goes wrong

Flood damage, pile scour, overloading by unplanned plant, collision from vessels.

Quality assurance

Load rating posted, pile driving records, inspection after floods.

Examples

Sea viaducts in the Gulf, wetland viaducts in Florida, most Korean river bridges during construction.