Intake Shaft Grout Curtain for the Niagara Tunnel Project

A 10.2 km long x 14.4 m diameter tunnel is currently under construction to channel water from the Niagara River to Sir Adam Beck Generating Station, Niagara Falls, Ontario, Canada. The tunnel's intake structure was excavated and constructed under dry conditions after a comprehensive bedrock fissure grouting program was executed. The grout curtain was specified by the owner's representative, designed by GeoSupport Inc., and constructed in 2007 by Geo-Foundations Contractors Inc. The details of the design, construction and performance of the grout curtain are discussed in this paper. Regular cement-based grouts were used with a variable-dosage cocktail of specialty grout additives to combat the wide variety of rock and groundwater conditions encountered. Grouting of the bedrock was staged from the top of cofferdam cells, caisson wall and rock fill, with the treatment zone between 10 m to 55 m below normal water level. An automated batching system and real time monitoring system facilitated the injection of over 541 tonnes of cement (dry weight of cement) during 7 months of grout curtain construction. A total of 12,500 m2 of grouted vertical bedrock face was exposed after completion of excavation. The grout curtain succeeded in achieving the contractually mandated performance threshold of maximum 50 L/s seepage through the entire exposed face.