April 21, 2008

Municipal Water Supply

Capilano-Seymour filtration project’s twin-tunnel construction still faces delays

Richard Gilbert

staff writer

The construction of two tunnels between the Capilano reservoir and the new Seymour filtration plant has been delayed for three months due to concerns about the safety of underground workers.

Metro Vancouver, which operates the Greater Vancouver Water District, is constructing the $600 million Seymour-Capilano water filtration project to improve drinking water quality in the Vancouver metropolitan area.

The project includes the construction of the Seymour-Capilano filtration plant, the Capilano Pumping Station and twin tunnels under Grouse Mountain with a combined length of 14.2 kilometres.

The twin tunnels will transport water from the Capilano reservoir to the filtration plant for treatment and the treated water will then return to the reservoir, by gravity, through a parallel tunnel for distribution.

Construction on the $200 million tunnel project started in late 2004, with crews clearing land and blasting the Seymour shaft.

By mid 2006, the Seymour shaft was complete and the tunnel-boring machines (TBMs) were launched to begin creating the tunnels.

But, after a year and a half of work, Metro Vancouver was advised by the Germany-based contractor that it was halting work due to concerns about the safety of underground workers.

“Work was halted on the raw water tunnel, which pumps untreated water from the Capilano reservoir up to the filtration plant on Jan. 7. The treated water tunnel was shut down on Jan. 10,” said Doug Neden, project manager in the engineering division of Metro Vancouver.

“They were worried about the workers, due to overstressing, rock fracturing and rock breaking out. Weak and overstressed rock caused more problems than anticipated.”

The contractor stopped work on the tunnel where the TBM had made the most progress under the mountain. The TBM in the other tunnel was also stopped due to concerns about running into the same problems.

“The treated water tunnel was about 300 metres behind the raw water tunnel. The contractor was concerned that if work on the second tunnel continued, they would run into the same type of rock,” said Neden.

There had been 10 incidents with falling rocks, with three of these incidents resulting in injury. Two of the incidents caused an injury that required first aid and the other resulted in lost time for the worker.

According to media reports, a worker was installing steel mesh on the top side of the tunnel, just behind the cutting head of the TBM.

He was struck by a rock that came loose from the tunnel’s crown and fell more than a metre.

WorkSafe BC directed the contractor to halt work until the hazardous condition has been eliminated or controlled.

“The areas where the tunnel boring machines were undertaking construction are at 4.1 km and 3.8 km of the 7.1 kms tunnels. Those areas are still roped off for about 60 metres and the machines are still there,” said Neden.

The decision to stop work led to the temporary layoff of workers, many of whom were brought in from overseas.

“We have 90-100 workers on this project including construction site and office staff. We laid off about 30 people in March,” he said.

Metro Vancouver and their consultant engineer made recommendations to the contractor for solving the problem.

The contractor rejected a plan from Metro Vancouver engineers to deal with the problem and are in the process of reviewing a second plan.

While waiting for this decision, a limited amount of work has resumed on the tunnel.

“They have started work away from the tunnel boring machines in the tunnel. We are going in to do final support work about 300-400 metres away from the tunnel boring machine,” said Neden.

“We are doing shotcrete with steel mesh and bolts in the required areas.”

Before the work stoppage, construction was occurring seven days a week, up to 24 hours a day.

Tunnelling was done 18 to 20 hours a day, with the remaining hours spent performing TBM maintenance and changing the cutter heads. Tunnelling progress usually averages 10 to 20 metres per day.

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