Fast-track drill+blast in Canada
Apr 2010
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Impressive drill+blast excavation had a large-scale water transfer tunnel in Canada completed in record time. Clair Murdock and Ron Glowe, independent bidding and explosives consultants tothe contractor, describe the undertaking.
- The Rupert Transfer Tunnel in Québec, Canada is 2.9km long and is designed to transfer 800m3/sec of water from the Rupert River watershed into the Eastmain River watershed to double the generating capacity of five hydro plants on the Eastmain River - two new generating stations now under construction - the 768MW Eastmain-1-A powerhouse and the 150MW Sarcelle powerhouse - and three existing schemes.
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The completed excavation of the Rupert Transfer Tunnel
- The 2.9km long x 18.6m high x 12.7m wide pay-line tunnel was excavated on a drill+blast topheading and bench sequence using modern computer-controlled jumbos to progress the heading from both ends, working alternating rounds, and employing crawler hydraulic drills for vertical charge holes to advance the 10m high bench from one end only. Large side-dump loaders and 50 tonne trucks mucked out both the heading and bench. Working on a schedule of two 10hr shifts/day, five and a half days/week, the 651,300m3 of Canadian Shield granite rock was excavated in 13 months.
- To put this into a TBM context, the excavated volume equals 23km of 6m diameter TBM tunnel. To excavate the same rock volume in the same amount of time, that hypothetical 6m TBM would have to advance at an average of 1,772m/month.
- The total 229m2 tunnel was excavated in 2007 and 2008 working through a tough sub-Arctic winter with temperatures reaching -40° Celsius and avoiding the need to endure a second.
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Loading a topheading round with a Sandvik T11A jumbo in the foreground
- In addition to the 2,908m long tunnel, the Can$5 billion investment by Hydro-Québec, the largest hydropower generator in the world, includes four dams, a spillway on the Rupert River, the two new powerhouses and two forebay lakes.
- Two 3-boom Sandvik (Tamrock) T11A data jumbos, with man-baskets worked in the 8.6m high x 13.7m wide (102m2 excavated) topheading to remove 282,000m3 of rock. The 5.8m deep x 57mm diameter charge holes in the topheading round pulled on average 5.4m to break about 524 bulk m3 of rock, or about 1,400 tonnes of muck per round For 15m at each end, the pilot-and-slash technique was used, with the pilot rounds limited to a 2.5m pull, leaving at least 2m of rock to the pay-line for the subsequent slash round. For the 300m drive under Lake Sillimanite, probe drilling was required for a minimum 10m beyond the topheading face.
- Five hydraulic crawler drills were used to excavate the 369,300m3 of the 10m high x 12.7m wide (127m2) bench. Each 10-12m bench round broke out about 1,524 bulk m3, or about 4,100 tonnes of rock. Cat 988 side-dump loaders, into a fleet of up to six Cat 773 trucks of 50 tonne capacity mucked out each topheading and bench round. Power scaling was done with Cat 365 hoes.Each round was bolted and meshed to the face before drilling of the next round was started.
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Fig 1. Plan of the Rupert Transfer Tunnel
- The job was bid in January 2007 and awarded for $57 million to the low bidder, Simard-Beaudry Construction, in late March 2007. Four new drill jumbos were ordered conditionally from Sandvik (Tamrock) in February to gain time on the schedule. The fleet of jumbos comprised two data T11's, one non-data T11, and a 2 boom T8 for rockbolting. Mobilization, clearing of the portals and construction of temporary power lines and access roads started in April, 2007.
- After site mobilisation, pilot-and-slash work at the downstream portal started in September 2007. Due to unforeseen rock excavation difficulties, the upstream portal work was finished later than planned, concluding in October 2007. Tunnelling on a sustained basis from both ends started in mid-October 2007. After a two-week shutdown for the Christmas/New Year holiday topheading work finished in early June 2008, completing the topheading in a total eight months. Benching was completed by early November for a benching duration total of five months and an overall tunnel excavation of 13 months and substantial demobilization of the site by December 2008, avoiding a second winter.
- The tunnel was finished 12 months ahead of the owner's diversion schedule requirement with filling of the Rupert River forebay started in November 2009, a year after all tunnelling was completed.
- As the largest hydroelectric generator in the world, Hydro-Québec currently operates 59 hydroelectric powerhouses equipped with 336 turbines and producing 33,680MW. The generator also owns and operates the largest underground powerhouse complex in the world, with the 22 units installed at the Robert Bourassa (LG-2) and LG-2A site having a total capacity of 7,722MW. The added water delivery of the Rupert Transfer Tunnel will add substantially to the energy benefits of the powerstations in the Eastmain River chain of installations.
- Further details of the project will be described in a paper by Clair Murdock and Ron Glowe to be presented at the ITA World Tunnel Congress in Vancouver in May.
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