Penstock Grouting at Whitehorse Rapids Dam in Whitehorse, Yukon-PPT Presentation

PPT Presentation

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Whitehorse Dam in Yukon, Canada, experienced bulging and deformation in its WH1 and WH2 steel penstocks. WH2 damage was discovered during a 2020 inspection; similar, less severe damage had previously been observed in WH1. Investigations using visual inspection, 3D scanning, geotechnical drilling, instrumentation, testing, and geophysics identified the damage as pipe overstressing and buckling. The likely cause was settlement of loose bedding sand, which allowed the pipes to sag between supports; winter construction may have contributed.<br /><br />Repairs combined structural work—pushing out bulges and welding reinforcement plates—with permeation grouting to fill voids and stabilize the bedding sand. Before fieldwork, groutability tests helped refine the approach and highlighted excessive grout bleeding as a quality concern.<br /><br />Ultrafine cement grout was injected through nozzle arrays along the lower portion of each penstock. Crews monitored pressure and grout volume in real time. WH2 was grouted over seven days in December 2020. A faulty pressure sensor initially led to unexpectedly high grout pressures and large grout takes; after it was repaired, additional pressure gauges and procedural adjustments improved control. Lessons from WH2 informed the WH1 plan, including incorporating general-use cement, limiting ultrafine cement, and adding a maximum-volume termination criterion. WH1 was grouted over four days in February 2021, with lower grout takes overall and targeted additional nozzles where seepage or other concerns arose.<br /><br />The project used multiple investigation methods and specialist expertise, with the grouting plan adapted through testing and field experience. Slab Impulse Response results appeared useful for assessing conditions before and after grouting and were generally consistent with observed grout takes. Both penstocks returned to service and have operated without reported issues.

Keywords

Whitehorse Dam

Yukon

steel penstocks

buckling

pipe overstressing

settlement

permeation grouting

ultrafine cement grout

geotechnical investigation

structural repair