Muskrat Falls North Dam Grout Curtain with Gin Principle-Paper

Paper

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The paper describes installation of a GIN (Grouting Intensity Number) grout curtain beneath the North Dam at the Muskrat Falls hydroelectric project in Labrador. The work aimed to seal fractured and weathered bedrock and limit seepage, with a target permeability of no more than 1 Lugeon.<br /><br />Grouting was carried out from a narrow, 450-m-long drainage gallery while the RCC dam was being built above. Crews drilled 243 holes, averaging 30 m deep, in a single-row, split-spacing sequence through primary, secondary, tertiary and quaternary holes. A stable, relatively thick grout mix was used throughout, with automated equipment monitoring pressure, flow, volume and GIN values in real time. Grout batching took place outside the gallery, requiring careful coordination of drilling, pumping, water supply and waste removal. Cold weather also affected grout properties and operations.<br /><br />The project was completed in seven months, using about 8,000 m of drilling and 290 tonnes of cement. Two verification holes were cored in areas with high grout takes; subsequent water-pressure tests recorded less than 1 Lugeon, meeting the design requirement. The curtain has since resisted more than 30 m of hydrostatic head and remained effective through severe temperature cycles.<br /><br />Key challenges included restricted workspace and access, limited capacity for hoses and cables, remote-site supply logistics, difficult drilling conditions and lost packers. The authors also note evidence that high pressures in deep stages may have caused hydrofracturing, potentially explaining unexpectedly high grout takes. The paper highlights the importance of trial testing, pressure control, quality assurance and advance planning when applying GIN grouting in confined galleries and cold climates.

Keywords

GIN grouting

grout curtain

North Dam

Muskrat Falls

hydroelectric project

seepage control

bedrock permeability

Lugeon testing

RCC dam

cold weather grouting