Tough Diggin’

Staff Report

When it comes to drilling and blasting into shear rock, few projects, regardless if they’re mining related or not, can match that of what contractors faced when they were recently hired to build a tunnel in Northern Quebec.

Faced with the task of the full-face blasting of a 2.9-km transfer tunnel for Hydro-Quebec in Northern Quebec, contractor Simard-Beaudry Construction Inc of St. Eustache, Quebec, ran into more bad ground than anticipated during its work on the 18.7-by-12.7 m tunnel.

The transfer tunnel itself, while not a true mining project per se, is part of a massive hydroelectric project to redirect nearly three-quarters of the Rupert River flow into new and existing power generating turbines, creating an additional 8.5 terawatthours annually — enough to supply Quebec City for a year.

Hydro-Quebec is spending $5 billion on the project to construct four dams, a spillway, 74 dikes, two diversion bays and the 2.9-km transfer tunnel. The utility is looking to have everything fully commissioned by spring 2012.

Diversion bays

Diverting the Rupert’s flow north to the power stations requires two diversion bays: the Rupert forebay and tailbay. Diversion bays are different from reservoirs in that they are not used to stock water. The Rupert bays will cover a total area about 346 km.

Hydraulic and retaining structures are planned to contain the rerouted river in the two diversion bays and channel the flow north toward existing reservoirs and power stations. The transfer tunnel will move water from forebay to tailbay. All of these structures are designed to minimize the land areas being flooded.

Simard-Beaudry first approached the face of the Rupert transfer tunnel in August 2007. The construction contractor ran two shifts, 24/6, with 115 workers and four tunneling jumbos on site.

Two jumbos drilled together, side by side. During blasting and mucking, the jumbos trammed to the other end of the tunnel and drilled. Both ends were excavated like this for 10 months, finally meeting in June 2008.

“We were fortunate that we could access both ends of the tunnel,” said Jimmy Accurso, vice president of Simard- Beaudry. “In a lot of jobs you don’t have that kind of access.”

The initial tunnel’s dimensions are 8.7 m high and 12.7 m wide. Crews then benched another 10 m from the floor to reach the tunnel’s full dimensions. When commissioned, the Rupert transfer tunnel will handle a flow of 800 m2 of water at a velocity of about 3.3 m2 per second.

Bad ground

Creating the initial tunnel required 152 holes that would bring down about 800 m3 tons of rock per blasting round. Each hole would be more or less the length of the entire 6.1-m drilling rod, said Accurso.

“In terms of production, we were able to achieve our goals in a reasonable amount of time. Excavating crews experienced their onsite-best when they completed 24 blasting rounds in six working days,” said Accurso.

What slowed the process was bad ground. Faults and other bad zones would cause the drills to get stuck or otherwise inhibit penetration rates. This affected timelines and budget.

“We hit bad ground a lot more than we thought,” said Accurso.

Simard-Beaudry was able to compensate for these interruptions with technology found on the Sandvik DT1130-C Data tunneling jumbos it used on the job. The computer-controlled three-boom jumbos feature TDATA, an automatic control system for all drilling functions and boom positioning under the supervision of a rig operator.

“It does a fantastic job,” said Accurso “The DT11 positions booms and drills in the pattern programmed into it. The operator watches over to see if a rock is bad or a drill gets stuck. Otherwise, the machine does the work on its own.”

Accurso said the system made it easier for his company to standardize a drilling time per round. Information from the drill’s computer system was helpful in anticipating bad zones.

“If there’s a change in rock conditions, you notice right away with the penetration rates and the amount of pressure,” he said. “We knew exactly how the rock was behaving. We knew if there was a fault or something coming up, and we could plan for it.”

The tunneling jumbo, with its four-wheel-drive, wheel-steered carrier was very user-friendly; so much so that Accurso said he was able to quickly train operators who had never used it before.

While the work just mentioned is newsworthy insofar as drilling technology is concerned, one other project that is purely mining related happened recently at the Red Lake Gold Mine in Lively, Ont.

In this particular case, the longest and largest diameter raise ever bored in the Canadian Shield was completed by Cementation, a mine contracting and engineering company that specializes in major rock boring projects.

The Red Lake mine is owned and operated by Goldcorp and is located in Northwestern Ontario near Balmertown and Red Lake. Widely recognized as one of the richest gold mines in the world in terms of grade, the mine is the flagship operation of Goldcorp.

The Red Lake No. 3 shaft is a key element of the company’s expansion project. The shaft is now a 6.5 m diameter bore sunk to a depth of just over 1953 m.

Because of this remarkable structure, Sandvik Mining and Construction has caught the attention of North American hard rock mines regarding large-diameter raise boring since Cementation broke the record with an 5.6-m diameter bore 705 m long.

This project, the 10th longest and largest diameter raise in the world, was completed without incident, first aid, medical aid or lost-time injury.

Reg Blanchard, product line manager for raise boring for Sandvik Mining and Construction, said that because of his company’s network of raise boring teams, they were able to supply the equipment for the Red Lake job in record time. Sandvik was involved with the technical support and service support teams on the project primarily because Cementation used its raise bore heads for 100% of the job.

“Originally the project called for a shaft 3.7 m in diameter but when it was later changed to 5.6 m, the adrenalin started pumping because that size of hole had not been tried in North America before, certainly not in hard rock,” said Blanchard.

“We located an 5.6 m raise boring segment in Africa.”

Two 5.6-m diameter shafts were drilled at Red Lake. During the first 341 m-long raise, the Sandvik raise boring crew learned at lot, according to Blanchard.

“This was our first time working with such a large reamer.”

It was a huge undertaking and like so many other mining projects in Canada, it became a North American first that has attracted worldwide attention.

Based on information provided by Sandvik.

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