Rotary screw (helical) piles

How bridges get built · Driven piles · Rotary screw (helical) piles

Also called: helical pile, screw-in steel pipe pile, rotary penetration pile

How it is done

Design the helix or toe wing (single or multiple helices, or a wing at the toe of a steel pipe) for the bearing layer and the installation torque, and check the pipe for torsion.
Set the pile in the rotary head of a crawler rig and start it plumb; advance by rotation with crowd force, keeping the advance per revolution close to the helix pitch so the soil is displaced, not augered out.
Add sections by welding or bolted couplers and inspect each joint.
Record torque and depth continuously; stop at the target torque with the minimum embedment in the bearing layer.
Calibrate the torque-capacity correlation for the site with static or dynamic tests on the first piles.
Cut off and connect to the cap with a head plate or concrete plug.

Key numbers

Light helical pilesshafts about 70-300 mm with helices 200-600 mm.
Rotary-penetration steel pipe piles (Japan)pipes to over 1 m with toe wings about 1.5-2 times the pipe diameter.
Spoil and vibrationpractically none.
Productivityabout 5-15 piles per shift.

Where it fits

Urban sites with noise limits, quick foundations for temporary works and small bridges, retrofit under existing structures with limited headroom.

Where it does not

Gravels and cobbles that stop the helix; large loads.

Choosing it

Choose screw piles over driven piles where noise, vibration and spoil are not allowed and loads are light to moderate.
Choose them for temporary works and falsework that must be removed: they can be unscrewed.
Prefer bored or driven piles in gravel, cobbles and rock, or where large lateral loads demand large-diameter, thick-walled sections.

Plant, pace and money

PlantRotary rig with torque monitoring.

Productivity5-15 piles per shift.

CostUSD 150-300 per metre for 600-800 mm.

Risks and controls

What goes wrong

Helix damage, torque-capacity correlation drifting with soil type.

Quality assurance

Torque logs per pile, load tests on a sample.

Origins

Alexander Mitchell patented the screw pile in 1833 and used it for the Maplin Sands lighthouse (1838-41); Victorian piers and colonial bridges followed. Large rotary-penetration steel pipe piles with toe wings were developed in Japan in the late 20th century as low-noise, spoil-free bearing piles.

Examples

Japanese highway viaducts near housing; falsework foundations.

Case studies

Maplin Sands Lighthouse, Thames estuaryUK · 1838-1841Mitchell's first major use of screw piles: a lighthouse on iron screw piles in soft estuary sand.

West Pier, BrightonUK · 1866Eugenius Birch's pier stood on cast-iron columns screwed into the seabed, the method used for many Victorian seaside piers.