Exhibition Station: sealing and reopening drains in a live culvert

Building Exhibition Station on the Shatin to Central Link meant diverting permanent storm drains into a box culvert while they were still carrying water. Every seal and every bulkhead had to be fitted, and later removed, by divers working inside the culvert.

Survey (July 2021)

Working in pairs with a standby diver, the team entered through the manholes, measured the Ø900 mm branch drain for its seal plate, found the leaks at the existing temporary plate by knocking from one side while a diver on the other watched under positive pressure, and searched more than 100 m up the culvert for a Ø1,200 mm branch, found as a 1,300 × 900 mm opening.

Seal plates

We measured each opening and designed a segmented steel seal for it: Ø900, Ø1,030, Ø1,200 and Ø1,500 mm branches, and the 2,100 mm shaft at Leighton Road. Each seal is a 10 mm angle frame anchored with expansion bolts, 20 mm locking plates and bolted closing panels, sized so a diver can carry and fit every piece.

Removing the bulkheads (May 2022)

When the diversion was complete, two temporary bulkheads of 1.3 × 1.3 m and 2.3 × 2.8 m, both 20 mm plate, came out:
1. Drill the culvert roof and fix lifting eyes; hang a 1.5-tonne chain block on each plate.
2. Cut all the nuts with a pneumatic saw and pull the plates free.
3. Fit floats to the plates to take their weight, and pull them by rope to the manhole.
4. Lift them out by crane.
5. Cut off the remaining bolts and fill the holes with cement mortar.

Earlier, in 2019, we also planned the clearing of settled grout from the culvert.

From the drawings

The same seal design was used at Kai Tak River for Ø1,200 and Ø1,350 mm pipes. In February and March 2021 a diver also broke out about 30 m³ of hardened cement grout from inside a Ø1,030 mm sewer with a pneumatic breaker, before the 12 m and 28 m runs were sealed.