At Bruce Nuclear Generating Station near Tiverton, Ontario, the construction of a deep geologic repository (DGR) is being considered by Nuclear Waste Management Organization (NWMO) for the long term storage of low and medium level radioactive waste. As part of the feasibility study for the DGR, Geo-Foundations was busy from June through October 2011 working day and night performing drilling and grouting of 200-metre deep holes for Phase 1 of a deep grouting trial being executed to determine parameters for the pre-treatment of the underlying rock formation prior to excavation of the proposed DGR shafts. Pre-grouting of the rock is necessary to permit excavation under controlled inflow conditions; Phase 1 of the grouting trial was carried out to test and establish drilling and grouting methods specific to this site.
With the consultant having placed considerable importance on the drilling accuracy at depth (with a specified tolerance of 0.5 degrees, or +/- 1.0 metre in plan at 200 metres depth), the drilling method used was the Wassara water hammer system, chosen specifically for its ability to drill straight, clean holes with reasonable speed. Gyro survey methods were used to periodically check hole alignment and determine when corrections were required, at which point the Navi-Drill system was utilized to make minor hole alignment corrections to maintain the required tolerance. Prior to grouting, an acoustic televiewer was used to supplement the water test data in order to better establish the nature of the rock fractures. Phase 1 of the test program ultimately consisted of 3 primary holes and 1 secondary/verification hole each having been drilled, water tested and grouted. The successful implementation of Phase 1 has resulted in the decision to proceed with Phase 2 in 2012.
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