March/April 2007

Engineering Exchange

Engineering the North

By H. Weldon

Last year, EBA Engineering Consultants Ltd. celebrated its fortieth year in the consulting business, having successfully grown its key areas of specialization in geotechnical engineering, environmental sciences, and transportation. In the early 1970s, EBA formed their exclusive “Arctic team,” which focused on engineering projects north of 60 for the oil and gas industry, in such frigid environments as the Mackenzie Delta and the Beaufort Sea. When the mining industry extended its arm into the Far North in the mid-1980s, several companies turned to EBA for their knowledge and expertise in handling the challenges of permafrost. “We didn’t have to look for contracts; mining came to us,” said CEO Paul Ruffell.

Between 1998 and 2004, EBA designed and oversaw the construction of five water control dams at BHP Billiton Diamonds Inc.’s EKATI mine. EBA engineers utilized their knowledge of frozen core construction and applied similar technology for an experimental toe berm to surround waste rock piles to inhibit discharge, possibly the first of its kind so far north.

The toe berms, made up of frozen overburden, abut a granite rockfill blanket at the fringes and are capped with rockfill. The initially dry granite waste rock is spread out inside this structure, and waste rock is then piled up in 15-metre-thick layers inside the toe berm. The waste rock naturally freezes by the end of the first winter, and water infiltrating into the pile during the spring and summer initiates pore-ice formation in the blanket and core of the pile. The toe berm also reduces seasonal runoff at the fringe. The top five metres thaws and the rest remains frozen, providing an excellent long-term reservoir for pore-ice. Kevin Jones, senior project director, Arctic Region, EBA, pointed out an exciting and unexpected discovery. “The arctic winds blowing across the waste rock created convective currents in the porous waste rock that in turn supercooled the waste rock maintaining the frozen core colder than the natural permafrost ground in the area.”

EBA monitors the site regularly, measuring the temperature of the waste rock, and the BHP Billiton environment department monitors surrounding water bodies on a monthly basis, to confirm that contaminates are not being released from the waste rock piles. “Any possible impact on surrounding water bodies - no matter how slight - is undesirable in the aggressive regulatory regime within which the mine operates,” Jones explained.

The initial toe berms at the Panda waste rock pile at the EKATI mine were found to be effective; therefore construction of similar toe berms at the Fox pit were soon underway. Toe berms will be employed at new waste rock piles as additional open pits are developed.

EBA took a special interest in the Tibbitt-to-Contwoyto ice road in 2006. The 570-kilometre-long ice road, of which nearly 85 per cent is built over lakes, is a lifeline for a handful of mines in the Far North. It is usually open only eight to 12 weeks each year and in the order of 8,000 truckloads of supplies are transported north from Yellowknife during this short operating season. In March 2006, the road was shut down prematurely following an unseasonably warm winter. As a result, mines like EKATI and Diavik Diamond mine were forced to fly in supplies (particularly diesel fuel) as well as machinery and parts, with an estimated whopping $30 to $50 million price tag.

EBA’s Don Hayley, principal engineer, and Samuel Proskin, senior project engineer, have begun research to optimize understanding of the ice road. Several factors are involved in ice road stability. Warm weather is of course the primary one, but also important is the route the road follows. Blowouts can occur at the sides of narrow lakes that the road crosses. Erosion of short sections of the road can occur due to undercurrents and water erosion. The ice actually deflects downward and then rebounds after each truck passes. Our own efficiencydriven society is also to blame - trucks are multi-axle and bigger, carrying heavier loads, which in turn adds stress to the road.

For the past decade, rudimentary and intermittent testing of the ice road involved drilling ice cores. Repair, when possible, has involved covering poor sections of ice with rig mats. EBA is developing a system of continuous profiling with radar to measure ice thickness. Continuous monitoring could result in repairing a weak area before the section has eroded, preventing accidents and closures. This technology is still in its early stages and in past years has been labour-intensive to interpret the data, preventing it from providing real-time interpretations. However, EBA has just completed developing its next generation software and processing programs to interpret the data from the radar on-the-fly and has been using it throughout the current winter.

EBA has more than 600 engineers, scientists, technologists, and support staff from 10 offices located in western and northern Canada. The mining section consists of environmental services, mine waste management, regulations and permits, and site development. EBA provides design and construction expertise to sub-arctic and alpine mining projects. Examples of their solutions include frozen core dams to achieve “zero discharge” facilities, a frozen cell dock to withstand large ice flow impacts, use of frozen backfill to facilitate a cost-effective underground operation, and thickened tailings deposition schemes to create permafrost tailings.

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