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Vancouver digs deep to reduce earthquake risks

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by Richard Gilbert

Metro Vancouver is planning on building water tunnels beneath the Fraser River and Burrard Inlet to ensure the region’s key water supply infrastructure can withstand a major earthquake.
Vancouver digs deep to reduce earthquake risks

Water Supply Infrastructure

Metro Vancouver is planning on building water tunnels beneath the Fraser River and Burrard Inlet to ensure the region’s key water supply infrastructure can withstand a major earthquake.

“Right now we are just at the stage of detailed design, which includes finishing contract documents, specifications and drawings,” said Frank Huber, division manager of engineering support and technical services with Metro Vancouver.

“We are within a month of completing this and are also trying to get a team together for the construction stage. We are just about there after four to five years of investigations and design.”

The Port Mann tunnel is expected to be one kilometre long and 3.2 metres in diameter, with a pipe inside hauling water from Coquitlam to North Surrey.

“Within Metro Vancouver, we have a program to build a water supply system to survive a major earthquake and provide water immediately after an earthquake,” he said.

“The new Port Mann tunnel is a key component in a system that will allow the provision of water after an earthquake.”

According to Huber, tunnels are designed to withstand the worst possible earthquake scenario.

That would be a quake of about an eight or a nine on the Richter scale that would hit 200 or 300 miles away off the coast of Vancouver Island or a closer earthquake with a magnitude of about seven on the Richter scale.

The existing pipeline crossing, which was constructed in 1974, consists of a 1200 mm diameter welded steel pipe about one kilometre long.

The pipeline crosses the Fraser River just downstream of the Port Mann Bridge and is a primary water supply link to municipalities south of the river.

There is no damage potential to the pipeline for a minor earthquake, but the crossing would fail during a moderate or a major tremor.

In 1997, this crossing was damaged by river bed scour, which caused significant water supply problems to several municipalities.

Water restrictions were placed on residents and water was rerouted from other crossings.

The repair was completed in 1998 and consisted of replacing the damaged section of the watermain and providing a limited protective apron to protect against future scour.

“We patched the pipe and figured it would last for 10 to 15 years, which would give us time to come up with a tunnel design for a new crossing that would be seismically secure and secure from river scour or erosion,” explained Huber.

The tunnel will be constructed using a Tunnel Boring Machine similar to the one used on the construction of the Canada Line.

The machine will install a lining as it goes through soft ground and sandy deposits.

The pipe will fit inside the tunnel, which will be filled with cementitious grout.

“All three structural components will act in unison to give the strength and ductility needed to resist seismic forces or major earthquakes,” said Huber.

In October 2008, Metro Vancouver issued a Request for Proposals (RFP) for the provision of construction management services for the Port Mann water tunnel.

The RFP, which was due in November, generated responses from Sandwell Engineering, Hatch Mott MacDonald and Pacific Liaicon and Associates.

The contract was awarded to Hatch Mott MacDonald.

“We still have to get the permits in place from the Fraser River Estuary Management Program and the Port of Vancouver,” said Huber.

“We hope to have the prequalification stage for construction to go out in June or July, but that will depend on the permits. We will short list the contractors through prequalification and hopefully in the fall we will be in a position to make the final award.”

The budget for the design, construction and pipeline work for the project is about $200 million.

Construction is scheduled to start in January 2010 and the project will be completed in 2013.

The Second Narrows tunnel will be even bigger, at 4.1 metres in diameter, with the pipe inside being three metres in diameter. The pipeline would supply the bulk of water from the Seymour watershed across the Burrard Inlet to Burnaby.

“We just finished the conceptual design on the Second Narrows tunnel, which means we are at where we were five years ago on the Port Mann tunnel. But, we hope to get through the design phase faster and start construction in three years.”

Metro Vancouver’s conceptual design for the tunnel has identified a need to locate the south exit of the tunnel in northwest Burnaby within city-owned land at Montrose Park.

The three North Shore crossings that currently supply water were built in the 1940s and wouldn’t survive even a minor earthquake.

The Second Narrows tunnel is estimated to cost about $150 million.

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