Construction methods · Caissons and marine foundations

Steel pipe sheet pile (SPSP) well foundation

Interlocking steel pipe piles are driven in a ring; the interlocks are grouted so the ring works as a rigid well, and a top slab ties it together. The ring is first the cofferdam and then the permanent foundation: a Japanese method that cut river and coastal pier construction time dramatically.

How bridges get built · Caissons and marine foundations · Steel pipe sheet pile (SPSP) well foundation

Also called: SPSP foundation, steel pipe sheet pile cofferdam foundation, koukan yaita

Concept diagram (TheBridgeEng)

How it is done

Drive 800-1,500 mm pipe piles with interlocks from a template into the bearing layer; the ring is 10-30 m across.
Clean and grout the interlocks so they transfer shear; dewater the inside with a tremie seal if needed.
Cast the top slab inside the ring, cut the piles to level, build the pier; the upper part of the ring can be cut off or left as protection.

Where it fits

River and coastal piers in 5-20 m of water with sandy or clayey beds, high lateral loads (ships, earthquakes), sites where a separate cofferdam would double the time.

Where it does not

Rock at shallow depth (piles cannot embed), very small piers (uneconomic).

Plant, pace and money

PlantBarge with template, vibro and hydraulic hammers, interlock grouting plant.

ProductivityA ring of 60-100 piles in one to two months; then the slab and pier.

CostUSD 3-12 million per pier; cheaper than caisson plus cofferdam where it fits.

Risks and controls

What goes wrong

Interlock leakage and grout quality, driving refusal on obstructions, corrosion.

Quality assurance

Interlock grout tests, ring verticality, dewatering watch.

Examples

Tokyo Bay Aqualine and many Japanese river bridges; increasingly used in Korea and Southeast Asia.