Diving 40 m down a flooded caisson shaft
Confined-space diving inside a Ø2,000 mm steel caisson about 40 m below ground: clearing sediment and cutting out the reinforcement underwater.
- Year
- 2012 · 2016
- Client
- Gammon Construction
- Location
- Caine Road, Mid-Levels; MTR pump house
- Status
- Completed
- Category
- Underwater & marine
A flooded caisson is one of the tightest places a diver can work: a steel tube 2 m across, 25 mm thick, with the working level about 40 m below the ground.
The water was pumped down to +69 mPD. Divers went down by man-cage to work at about +39 mPD, with a first decompression stop set inside the shaft. They cleared about 45 m³ of sediment and cut 114 Ø32 mm bars, each about 2.8 m long, which came out in 12 pieces of 5.5 to 7 tonnes by crawler crane. The caisson ring also held 14 Ø50 mm grout pipes and 20 Y40 bars that had to be cut.
At the surface: a mobile control centre, air supply, cutting system, continuous ventilation down the shaft, a signalman, a standby diver and a decompression station.
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