Tseung Kwan O submarine cable: relocating the beach manhole
Moving the beach manhole where an international submarine cable comes ashore, using precast units, underwater pipework and grout placed from a floating platform.
- Year
- 2012
- Client
- NEC
- Location
- Tseung Kwan O, New Territories
- Status
- Completed
- Category
- Underwater & marine
Where a submarine cable comes ashore it runs into a beach manhole, half in and half out of the sea. At Tseung Kwan O the manhole had to be moved, which meant building a new one in the tidal zone.
Five stages
- Remove the armour rock and excavate.
- Level the bed and place precast units of 9 and 13 tonnes.
- Install galvanised-iron cable pipes underwater.
- Fix steel formwork.
- Grout with concrete pumped from a truck on shore through pipes laid across a floating platform.
A silt curtain on floating buoys, weighted with geotextile, kept sediment inside the works area. We also prepared the hoarding design report for the shore side.
From the drawings
The client was NEC. The new beach manhole and duct went through the rock-armoured seawall from +5.5 down to −4.5 mPD: armour rock lifted by crane lorry, a 3 m open cut by backhoe on land and grab barge offshore, HDPE ducts, precast units and steel formwork, concrete pumped through pipes on a floating platform, then the formwork cut away underwater. About 1,575 m³ and 1,950 m³ of rock fill were reinstated.
Drawings
