Pui O sewage outfall: diffuser installation method
A nine-step method, prepared at tender stage, for installing a diffuser on the Pui O outfall inside a sheet-pile cofferdam built from a temporary jetty.
- Year
- 2020
- Client
- Union King Engineering Limited
- Location
- Pui O, Lantau Island
- Status
- Method design (tender stage)
- Category
- Underwater & marine
A sewage outfall ends in a diffuser that spreads the treated effluent into the sea. For the pre-bid on the Pui O outfall works in 2020 we worked out how to build it.
A temporary steel jetty on piles carries a crawler crane out from the shore. From there the diffuser site is enclosed in a cofferdam of 12 m sheet piles, about 280 pieces, braced with 305 × 305 mm walings, and about 1,350 m³ of seabed is dredged and later backfilled.
Nine steps
- Drive the sheet piles.
- Install the walings.
- Dredge inside a silt curtain.
- Inspect the existing pipe.
- Cut the pipe and fit the bend.
- Place the diffuser and the weighted pipe section.
- Fit the diffuser risers.
- Backfill and complete the diffuser.
- Extract the sheet piles and install the marker buoy.
Drawings
