Hydrodemolition Helps Put A Fresh Face on a Canadian Dam
At 610 ft (186m), the W.A.C. Bennett Dam on the Peace River in northern British Columbia is one of the worlds highest earth-filled dams. The BC Hydro-owned hydroelectric facility has the capacity to generate more than 13,000 GWh annually, supplying more than a third of the province’s power demand.
Years of water runoff and freeze-thaw infiltration had left numerous cracks in the half-century-old dam’s concrete spillway. In the summer of 2021, an extensive program to repair the cracks and prevent further erosion got underway. Work progressed slowly, as the general contractor was using jackhammers to remove decaying concrete and prepare areas for repair pours. Sensing there might be a better way to get the job done, the on-site staff of the project’s surface preparation subcontractor Walco Industries, Inc., suggested that robotic hydrodemolition technology would help accelerate the repair process.
Walco Industries in Campell River
Based in of Campbell River, B.C., Walco Industries is well-versed in applications of hydrodemolition on a wide range of infrastructure. Though the spillway presented a number of unique challenges, the team was convinced that the approach would be far faster and efficient than conventional methods.
Walco’s team made a convincing case to the general contractor and owner of hydrodemolition’s capabilities, and was asked to test the system on a 9.8-ft (3m) spillway crack. Using Aquajet 410v robotics and track system, along with a 20,000-psi water-pressure system that had been used for surface preparation, Walco’s team easily cut 18-in (25.4mm) deep profiles into the deep concrete at various lengths, angles, and slopes, all to the owner-specified International Concrete Repair Institute CSP 10 standard. In fact, the hydrodemolition equipment accomplished more during the two-day trial than had been completed through weeks of handwork. The results convinced the GC and BC Hydro to rethink the repair strategy for the summer 2022 construction season, and use hydrodemolition to remove a 1,783-ft3 (50.5m3) section of spillway. Because those cracks were located at 45-degree angles, Walco brought in two proprietary winch and spine hydrodemolition systems adapted to a platform that conformed to the slope. The winches were anchored to the spillway approximately 330 ft (100m) above the worksite, one winch per robotics system. The pumps were staged up on the roadway 656 ft (200m) away, while the operators of the robotics were able to work from a safe distance of approximately 82 ft (25m) from where the hydrodemolition was being done.
Two systems operating concurrently on two different segments of the spillway slope so good coordination was imperative. The angles during the removal were modified to create “key” cuts in the concrete to help with reducing the amount of removal needed to be done by jackhammer. The winch systems were used remotely by the operators overseeing the hydrodemolition robotics.
The demolition was completed in phases
After hydrodemolition portions were completed, the GC’s team would do their modifications, adding rebar and fresh concrete. Due to the degradation from years of weather, exposure, and the large aggregate from the initial build, the project team frequently encountered spalling, which, in turn, added Walco’s overall scope of work.
All water was transported to site at the beginning of the project via water truck and there was enough storage capacity on site that no further water was required for the duration of the project. Multiple booster systems were needed to move dirty water from the flip bucket to the primary tank, then to the treatment equipment. The water was then stored until it was pushed up again to a 11,100-gallon (42,000 liter) tanker. From there, the water was pushed to the high-pressure pumps that fed the robotics within the spillway. Once the job was done, the treatment system would balance the water pH, remove turbidity, and prepare the water for safe discharge into a nearby forest.
All in all, the system proved very efficient—so much so that Walco crews needed to stand down for a few weeks so that the concrete replacement would could catch up. This was due to BC Hydro’s requirement that the spillway be back up and running within 10 days if needed. Those efficiencies were welcome, as the project team had to temporarily evacuate the area due to nearby forest fires, and contend with unexpected hazards such as lightning and high winds. Still, hydrodemolition proved its value that summer, covering 2,225 ft3 (63m3), and providing many lessons learned that will be applied to future projects.