How bridges get built · Bored piles and deep foundations · Reverse circulation drilling (RCD)
Also called: RCD pile, reverse circulation bored pile, large-diameter marine bored pile
How it is done
- Install a standpipe casing through water and soft seabed; fill it with water or slurry to keep a positive head.
- Lower the drill string with a roller or PDC bit; rotate slowly and pump up the return flow through the string to a settling tank.
- Reach the socket depth, clean the base by continuing circulation, lower the cage and tremie the concrete.
Where it fits
- Sea and river pylon foundations, deep piles through soft sediments into rock, 2-3 m diameters, heavy loads.
Where it does not
- Small piles where a Kelly rig is far cheaper; loose gravel that keeps flowing into the hole.
Plant, pace and money
PlantRCD rig on a platform or jack-up, standpipes, high-capacity pumps, settling tanks, cranes, tremie plant.
ProductivityA 2.5 m pile of 60-80 m in a week including socketing; several rigs work in parallel at a pylon.
CostUSD 1,500-4,000 per metre from marine platforms.
Risks and controls
What goes wrong
- Loss of circulation in fissured rock, hole collapse if the head is lost, long cage lifts in weather.
Quality assurance
Slurry head kept above sea level, base cleanliness by sounding and sediment measurement, CSL and O-cell tests.
Examples
Sutong, Stonecutters, Incheon, Russky and most modern sea cable-stayed pylons; the game assigns RCD to pylons in deep water.
Related methods
Drilled shafts (bored piles) with casing or slurryBi-directional (Osterberg cell) load testJack-up platformsRock sockets and base treatment
Further reading
JGS 1531 · project papers on Sutong and Incheon Bridge foundations