McArthur Falls Generating Station is located 120 km northeast of Winnipeg, near Lac du Bonnet, Manitoba. Construction of the 8-unit station was completed in 1954 and it has a generating capacity of 55 MW when water conditions are ideal. McArthur Falls is ranked as the station with the world's largest hydroelectric capacity operating with the lowest head - just 7 metres waterfall.
The powerhouse and spillway structures at McArthur Falls are made of reinforced concrete and are separated by an 800 m long earth dam. The powerhouse containing the 8 units is 177 m in length, and the spillway structures consist of an east, a west and a centre gravity wall, together spanning a distance of 337 m. As part of Manitoba Hydro's ongoing commitment to dam safety and infrastructure upgrades, the spillway structures and powerhouse were retrofitted in 2010 with 92 high capacity post-tensioned rock anchors.
The drilling, water pressure testing, consolidation grouting, re-drilling, installation and post-tensioning of the rock anchors were all completed in twelve weeks. The downstream spillway anchor locations were only accessible via a 1.0 m wide opening at each end of the structure, and a 3.4 m wide access deck at the power house and spillway imposed several additional logistical challenges to the execution of the work. A total of 1700 lineal metres of drilling and re-drilling was completed over an eight-week period. The largest anchors had tendons consisting of 15 strands and were load tested to 3,118 kN applied tension. Load cells were installed at five anchors location to enable long term performance monitoring of the anchors.
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