The foundation of a high voltage tower situated at the crest of a steep, high ridge of weak rock in Southern British Columbia was at risk of being undermined. Through the decades since its construction, the ridge had eroded several meters, exposing one of the foundation grillages and leaving another at risk.
The weak nature of the sedimentary rock made it even more erodible than soil. Relentless frost, wind, and weather had broken and raveled several meters of the slope crest. This material loss had exposed the upper portion of the foundation grillage and removed the required soil mass needed for uplift resistance. It was clear that the transmission tower owner needed to act quickly by either moving the tower back or protecting the crest.
Line clearance restrictions and topography prevented a tower move, but the physical constraints of limited access and a high slope made foundation protection equally challenging. GeoStabilization International’s unique equipment and ability to seamlessly adjust the design throughout construction was the perfect combination for the job.
As with many of GeoStabilization’s jobs, the technical aspects were only a part of the project. Collaboration with First Nations, environmental sensitivities with the Mountain Beaver (Canada’s most endangered species), steep off-road access, and a fast approaching winter further complicated the work.
Weaving through all the intricacies, the final result was a work of art. Perched at the top of a mountain ridge, the solution involved a matrix of micropiles, tieback anchors, grout injection, shotcrete, and a GCS® wall build out. If you happen to be on a flight between Vancouver to Calgary, be sure to keep an eye open for it!
A variation of karst sinkhole grouting is the grouting of mined coal seams and workings located below existing infrastructure that exhibit the potential to propagate to the surface and cause sinkholes and/or subsidence.