Construction methods · Caissons and marine foundations

Large-diameter monopiles

One steel tube 3-6 m in diameter, driven or drilled to 40-70 m, carries a pier alone, borrowed from offshore wind. It removes the cap and the group: one pile, one pier, one lift. In bridge work it suits sea viaducts with many identical piers in sand.

How bridges get built · Caissons and marine foundations · Large-diameter monopiles

Also called: monopile foundation, single large pile pier

Large-diameter monopiles — concept diagram — Concept diagram (TheBridgeEng)

How it is done

Fabricate cans in a yard; transport on a barge; upend with a crane.
Drive with a very large hydraulic hammer through a gripper frame, or drill and grout where rock is shallow.
Weld or bolt a transition piece and cast the pier or set a precast pier on top.

Where it fits

Sea viaducts in 5-25 m of water with sand beds, repetitive piers, sites where marine crane time is the constraint.

Where it does not

Boulders and rock without drilling, very soft clay to depth, ship-impact piers where a group is stiffer.

Plant, pace and money

PlantJack-up or heavy-lift vessel with 1,000-2,500 kJ hammer, gripper, upending tool.

ProductivityOne pile per one to three days.

CostUSD 2-6 million per pier including the pile.

Risks and controls

What goes wrong

Pile run in soft layers, refusal, buckling of the tip on boulders, fatigue in the transition piece.

Quality assurance

Driving records, verticality (within 0.25 degrees), weld inspection.

Examples

Offshore wind farms worldwide; a handful of sea viaducts in northern Europe and China.