Timber piles

How bridges get built · Driven piles · Timber piles

Also called: treated timber piling, wood piles

How it is done

Select piles to ASTM D25 or the local equivalent: straight, sound, with specified tip and butt diameters; pressure-treat with preservative to the retention required for the exposure.
Fit a steel shoe at the tip in gravelly ground and a steel driving ring at the butt; trim the head square.
Drive with a light hammer (drop, single-acting or small hydraulic), limiting energy so the head does not broom and the pile does not split.
Stop at the required set or penetration; restrike in clay; reject and replace any pile that splits, breaks or drifts badly.
Cut untreated piles off below the lowest permanent groundwater level; treat the cut surface of treated piles that stand above it.
Cap with a timber or concrete cap, and in seawater wrap or jacket the piles against marine borers.

Key numbers

Butt diameter250-450 mm; tip at least about 150-200 mm.
Length6-20 m common, up to about 25-30 m in Douglas fir or southern pine.
Working load100-400 kN per pile.
Lifeindefinite when permanently saturated; decades when treated above the water table; a few years in warm seawater with marine borers if unprotected.

Where it fits

Temporary trestles and falsework, small rural bridges, historic replacements, soft ground with 100-400 kN per pile.

Where it does not

Any exposure above the water table without treatment; marine borers; hard driving.

Choosing it

Choose timber for temporary trestles, falsework and light or short-lived structures in soft ground where timber is cheap and loads stay below about 400 kN per pile.
Prefer prestressed concrete or steel piles for permanent bridges where the heads stand above the water table, in seawater with borers, or where hard driving is expected.
Untreated timber is acceptable only if it stays permanently saturated; lowered groundwater from drainage or dewatering exposes the heads to decay.

Plant, pace and money

PlantLight crawler rig or crane-hung hammer.

Productivity15-30 piles per shift.

CostUSD 30-80 per metre.

Risks and controls

What goes wrong

Brooming of the head, decay at the water line, borer attack in the sea.

Quality assurance

Straightness and treatment certificates, driving records.

Origins

The oldest driven foundation: prehistoric lake dwellings in the Alps stood on timber piles, the Romans drove them under bridges and harbours, and Venice and Amsterdam stand on them; pressure treatment with creosote from the mid-19th century extended their use above the water table.

Examples

Temporary trestles for river bridges worldwide; Venetian foundations are the famous permanent case.

Case studies

Rialto Bridge, VeniceItaly · 1591The stone arch's abutments rest on about 12,000 timber piles driven into the lagoon clay, still sound because they remain saturated.

Old London BridgeUK · 1209Nineteen narrow masonry arches stood on starlings, boat-shaped enclosures of elm piles filled with rubble, which constricted the Thames and needed constant repair for six centuries.

Caesar's Rhine bridgeGermany · 55 BCA timber pile trestle across the Rhine built in about ten days, with paired piles driven at a rake and extra raking piles on the downstream side.