Breakthrough at first Site C diversion tunnel

BC Hydro says it reached a major Site C milestone over the weekend after crews punched through the first diversion tunnel for the Peace River.

Crews are excavating two tunnels to divert water ahead of September 2020 to build the earthfill dam across the main channel of the river. 

Excavations for the first tunnel began in July 2018, and stretches 700 metres long. Breakthrough was achieved on Saturday, June 22, BC Hydro said. The tunnel will be 12 metres in diameter, though just the upper half of the tunnel has been fully excavated so far, BC Hydro says.

"The tunnels are being excavated using roadheaders that grind through the rock and load it on to conveyors. The rock is then hauled away by truck and relocated elsewhere on site," the utility said in a news release.

Work to line the tunnel began last week, and involves using a slip form where concrete is pumped through small openings located around the slip form, enabling it to cure in a perfect circle outside of the form, BC Hydro said.

Each concrete pour takes between two to three days to cure, and liner thickness can range between 40 to 200 centimetres. Roughly 41,000 cubic metres will reinforce the tunnel walls, BC Hydro said.

The tunnels will have the capacity to handle 3,000 cubic metres of water per second once they are put into operation. On average, they will see river flows between 500 to 1,800 cubic metres per second.

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