Construction methods · Driven piles

Driven cast-in-situ piles

A steel tube with a closed shoe or a gravel plug is driven, then withdrawn while concrete is placed, leaving a displacement pile with an enlarged base (Franki) or a straight shaft. The bearing capacity of a driven pile with the flexibility of casting the length to suit the ground.

How bridges get built · Driven piles · Driven cast-in-situ piles

Also called: Franki pile, Vibrex pile, displacement cast-in-place pile

How it is done

Drive a temporary tube to depth by hammering on a dry concrete plug inside the tube (Franki) or on a shoe.
Form an expanded base by hammering out batches of dry concrete at the toe.
Place the reinforcement cage, fill with concrete while withdrawing the tube in stages, compacting by hammer or vibration.

Where it fits

Variable ground where pile lengths change from pier to pier; medium-load abutments; sites where high base resistance in gravel is wanted.

Where it does not

Very soft soils where the withdrawal necks the shaft; noise-sensitive sites.

Plant, pace and money

PlantSpecialist rig with drop hammer and tube.

Productivity4-10 piles per shift.

CostUSD 100-200 per metre.

Risks and controls

What goes wrong

Necking during tube withdrawal, cage lifting, base quality unknown.

Quality assurance

Concrete volumes per pile against theoretical, integrity testing on every pile.

Examples

Belgian and South African practice; older European motorway bridges.