April 21, 2008

METRO VANCOUVER

Crews move a large water main serving Richmond to make way for the Canada Line.

Relocation of utilities poses challenges for Canada Line’s Vancouver corridor team

Jean Sorensen

correspondent

Moving the water, sewer and other utilities along the Canada Line Vancouver corridor required ingenuity, innovation and “a lot of sleepless nights,” said a Metro Vancouver engineer involved with the project.

Les Ptak, P.Eng. was part of a team of Metro Vancouver, City of Vancouver, City of Richmond and Canada Line staff that worked in demanding and often tight time-frames to accomplish the task. Some of the larger pipes ranged in size from 42 inches to 72 inches and provided essential services to thousands of Richmond and Vancouver users.

One major move included relocation of two sections of a 42-inch water main that, on a typical winter day, supplies 90 per cent of Richmond’s potable water.

“We were really challenged in this operation and we had to use some innovative methods to ensure uninterrupted water supply to Richmond and South Vancouver,” said Ptak, Metro Vancouver’s senior project engineer.

Work on the main line could only be done on weekend nights, as service had to be back on line to sustain the heavy draw from Richmond’s awakening population.

Construction crews scrambled to get through a five-hour construction window to complete a new water-main tie-in or connection work. Ptak said that two new sections of water-main were first pre-constructed. Connecting these new sections and isolating the old main between the end points, required taking out of service and draining about 1.5 km of the existing watermain.

Completion of all connections required five nights of shutdowns. In the meantime, South Vancouver and City of Richmond had to be supplied using alternate means. It was decided to use the City of Vancouver’s water distribution system as a giant bypass in which water was re-introduced into the Metro main line downstream of the work section, so that the Richmond supply could be guaranteed.

The city’s water system is divided into distinct pressure zones.

“We had to introduce modifications to the city system and ‘break’ these zones to allow water flow between them in a controlled fashion,” Ptak said.

Extensive computer modeling of the Metro and the city water distribution systems was performed. A method of modifying the city system was devised, implemented and field tested to make sure it would work. Computer simulations allowed selection of the most practical solution and saved trial and error.

The utility relocation also included sewer lines.

“Some were very large,” Ptak said.

These relocations included construction of 1350 mm (54-inch) and 1650 mm (66-inch) diameter sewers as well as two 1,800 mm (72-inch) lines.

Similarly to water-main construction the new sewer sections were pre-constructed and end points connected into the existing system under low flow conditions.

Canada Line’s waterfront station also posed a challenge, said Canada Line’s Didier Samouilhan, as it was in the portion of the downtown area which was a bored tunnel not the cut-and-cover operation realized on Cambie Street. The waterfront station’s challenge, he said, came from the pedestrian level that had to be excavated from the west to east side connecting Canada Line passengers to SkyTrain and the West Coast Express. Several large utilities had to be relocated but because of underground location it was not possible to backfill. “We had to design a utility cavity (a concrete structure),” Samouilhan said, which would shelter the relocated utilities. It has also been one of the largest and most complex undertakings in the city.

Wayne Pledger P.Eng., retiring manager of the Canada Line project office, said he estimates that about one-third of the construction time was spent in relocating utility lines.

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