Tai Po Water Treatment Works: pumping sand from a deep culvert
Divers working from a man-cage at the bottom of a 2 m caisson removed 50–70 m³ of sand from a water culvert with a 3-inch sand pump.
- Year
- 2014
- Location
- Tai Po, New Territories
- Status
- Completed
- Category
- Hydraulic
Sand had settled in a culvert deep below Tai Po Water Treatment Works, 70–220 mm thick along the section from CH62 to CH70. The only way in was down a Ø2,000 mm caisson shaft.
We planned it in three stages over about 16 working days:
1. Sandbag bunds (3 days): divers build two 400 mm high bunds, about 320 bags, to isolate the working section.
2. Pumping (8–10 days): a diver-handled 3-inch sand pump (about 50 m³ an hour at 20 m head) moves an estimated 50–70 m³ of sand, with about 600 m³ of water, to a settlement tank at the surface.
3. Clearing up (3 days): the bunds and equipment are removed.
The set-up included a man-cage, a mobile control centre, surface air supply with a stage decompression station, and a continuous ventilation fan. Each shift ran with three or four divers, a supervisor, a tender and a signaller.
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