Jack-up platforms

How bridges get built · Caissons and marine foundations · Jack-up platforms

Also called: self-elevating platform, jack-up barge, SEP

Jack-up platforms — concept diagram — Concept diagram (TheBridgeEng)

How it is done

Carry out a site-specific assessment (ISO 19905-1): leg penetration and punch-through risk from CPTs or borings at each location, seabed obstructions, scour, and metocean limits for moving and for the elevated condition.
Tow or self-propel to location in a weather window and position with GNSS, anchors or tugs.
Lower the legs to touchdown and pre-load each footing, by ballast water or leg by leg, to at least the largest reaction expected in the design storm, watching for sudden penetration. Hold point.
Jack the hull to the working air gap above the design wave crest.
Work from the deck (drilling, piling, cap formwork) within the deck-load and crane charts; re-check leg penetration and scour around the footings periodically.
Jack down, extract the legs (jetting where they are deep in clay) and move to the next pier.

Key numbers

Water depthabout 5–40 m for construction jack-ups; larger units to 60 m or more
Pre-loadat least the maximum footing reaction expected in the design storm
Air gaphull above the design wave crest with a margin, commonly at least about 1.5 m
Leg penetrationfrom under 1 m in dense sand to over 20 m in soft clay
Movesabout one day between piers in good weather

Where it fits

Bored piles, drilling investigation, pile caps and pier construction at sea and in estuaries; water 5-40 m.

Where it does not

Very soft seabeds with punch-through risk, rock outcrops, strong currents beyond the leg capacity.

Choosing it

Choose a jack-up over a floating barge for bored piling, caps and pier work at sea: drilling and concreting need a steady platform for days at a time.
Prefer a temporary trestle in water up to about 5–6 m along long viaducts, where land plant can work from it continuously.
Prefer floating plant for short tasks, for water deeper than the legs allow, or on soft seabeds with high punch-through risk.
For long campaigns at one large pylon, compare a fixed platform carried on the permanent casings, as at Sutong, which frees the jack-up for other piers.

Plant, pace and money

PlantJack-up 30-90 m with 100-300 t crane, legs to 60 m.

ProductivityMoves take a day; the deck then works around the clock.

CostUSD 20,000-80,000 per day; the game's jack-up rate.

Risks and controls

What goes wrong

Punch-through of a leg during preload (the major jack-up accident), leg damage, collision.

Quality assurance

Site-specific leg penetration assessment, preload records, weather limits enforced.

Origins

Self-elevating platforms were developed for offshore drilling in the Gulf of Mexico in the 1950s; construction jack-ups derived from them became the standard platform for marine piling and, later, offshore wind installation.

Examples

All Gulf sea bridges, Hong Kong-Zhuhai-Macau, Incheon; the game assigns jack-ups to water piers deeper than 6 m.