Site C tension crack stable, according to BC Hydro

According to BC Hydro, a 400-metre-long tension crack on the north bank of B.C.’s Site C dam project remains stable. The crack appeared last month, causing 30 workers on a road crew to be reassigned while work stopped and the crack was assessed.

BC Hydro’s design team and technical experts in slope stability have undertaken ongoing geotechnical assessments. Monitoring instruments, including survey prisms and inclinometers, show that the slope around the crack is stable. In addition, a drill rig has been mobilized to drill and install additional instruments to gain a more detailed understanding of the crack, with experts currently examining the data, states BC Hydro.

"Safety is our top priority," stated David Conway, community relations manager for the project in an email to the Journal of Commerce. "This work needs to be done carefully and no construction activities are taking place in the area of the tension crack until a plan is in place to safely remove the material while maintaining slope stability."

Conway explained BC Hydro is developing a two-stage remediation plan. The first stage would include the construction of a toe berm to hold the area stable and this work could start soon. The second stage of the remediation plan would focus on allowing work to resume on the north bank.

BC Hydro expects to complete the remediation work for the tension crack within the overall project budget and schedule.

As part of Site C construction, work has been underway for the past 19 months to remove unstable soil to create stable slopes for eventual dam construction. During the construction of a haul road to support this excavation work, a tension crack appeared.

Conway noted that tension cracks are not unexpected in this area; however, this particular crack requires attention due to its significant 400-metre length.

He said while there was some initial movement of soil, it has now stabilized. This area of unstable soil was already slated to be removed as part of engineering new stable banks for dam construction.

The $8.8-billion Site C dam intends to meet future electricity needs by providing 1,100 megawatts of capacity and producing about 5,100 gigawatt hours of energy each year — enough to power the equivalent of 450,000 homes per year. It is scheduled to be complete in 2024.