The provincial government will spend nearly a million dollars to seismically upgrade a pair of bridges along the Trans-Canada Highway on Vancouver Island.

The twin 77-meter long bridges that cross the Cowichan River in Duncan were built before B.C. adopted modern seismic requirements. The first was erected in 1950, the other in 1978.

In the next few months, work crews will use four hydraulic jacks to raise each side of the bridge by a few millimetres, just enough to replace the existing bridge bearings with new seismic isolation bearings underneath.

Rod Mochizuki, project manager on Cowichan seismic retrofit.

Project supervisor Rod Mochizuki said the new bearings will act as a buffer between the bridges and their concrete foundations. (Gregor Craigie/CBC)

Project supervisor Rod Mochizuki said the new bearings will act as a sort of buffer between the bridge and the concrete foundation on either side of the river "so in the seismic event it will actually move within itself."

The hope is that the bridges will not only remain standing in a major earthquake but will be resilient enough to accommodate emergency vehicles immediately afterwards.

Janelle Erwin, regional deputy director with the Ministry of Transportation, said, "A fire truck is heavier than just your average passenger car so we want to be able to ensure that heavier emergency response vehicles have the ability" to cross the bridge after an earthquake.

More upgrades planned

There are other vulnerable bridges in coastal B.C that need seismic retrofits. After addressing the Cowichan River bridges, the ministry is expected to fix other spans along the Trans-Canada Highway to the north and south.

"We start looking at which corridors are most important and which are our lifeline corridors in the event of an earthquake," Erwin said. "Where do we need our emergency response? And where do we need to maintain those?"

Janelle Erwin, B.C. Ministry of Transportation

Janelle Erwin, regional deputy director with the Ministry of Transportation says other spans along the Trans-Canada Highway will also be upgraded. (Gregor Craigie/CBC)

Seismic 2000 Construction Ltd. of Aldergrove has been awarded the $998,900 contract to retrofit the Cowichan bridges. Work will start in late September and is expected to continue until next March.

Erwin said much of the work will be done under the bridge and will not be noticed by drivers, though each bridge will have to be closed while the bearings are replaced.

"What our contractor most likely will do is focus on one bridge at a time," she said. "So if we need to fully close the northbound direction, we would then be able to re-route traffic to the southbound direction to keep everybody moving. That sort of closures are allowed between midnight to 5 a.m."

Cowichan Bridge, Duncan, B.C.

The Trans-Canada Highway is expected to remain open during the upgrade work. (Gregor Craigie/CBC)