The Tibbitt to Contwoyto Winter Road in the Northwest Territories is the world’s longest heavy-haul winter road, and serves three northern diamond mines, including Diavik Diamond Mine, the Dominion Diamond Ekati Mine, and the DeBeers Gahcho Kue Diamond Mine.
For the past six years, Associated’s subsidiary, NOR•EX Engineering, has provided consulting services for design of the winter road, as well as quality assurance and environmental and safety program management. Our ice engineering specialists conduct independent assessment of ice integrity and ice thickness throughout the hauling season. NOR•EX also monitors and reports seasonal weather fluctuations and compares results to previous winters. This knowledge of current and historical weather conditions assists in developing contingency plans for construction and maintenance.
Project Manager, Tim Tattrie, tells us, “Over 85% of the entire winter road’s total length is across lakes. A significant risk to the Tibbitt to Contwoyto Winter Road Joint Venture hauling operation is the degradation of ice thickness and integrity of the ice cover along the road.”
During the annual winter road season, NOR•EX and contracted road maintenance crews monitor the ice sheet for growth and deterioration. With approximately 9000 truckloads transporting 300,000 tonnes of supplies over the winter road in a hauling season, the ice sheet endures both man-made and natural stresses. Heavy trucks cause the ice sheet to deflect and bend. Regional climatic conditions and temperature fluctuations can cause pressure ridges, cracking, and other hazards throughout the ice sheet. In areas of shallow water and rocky bottoms, threat of ice deterioration by ‘washing’ is a concern. Washing is a natural effect caused by water being displaced under the ice sheet, caused by the vertical deflection of the ice cover. This continual movement of water has a deteriorating effect on the overall ice thickness.
Road builders try to avoid shallow areas during the construction process; however, this is not always possible. The deterioration of the ice sheet at shallow areas can affect both operator safety and the annual hauling operations. The NOR•EX project team has been conducting field tests to better understand the magnitude and impacts of ice deflection, and has also evaluated options for reducing or eliminating the effects of washing. Tim says, “We have developed a solution to stabilize the ice sheet deflection in known, high-risk areas. Our team designed and installed ‘ice piers’ in areas of concern. The piers sit on the lake bottom, and provide a matrix, throughout which ice forms. The piers have been shown to eliminate washing and vertical ice deflection.”
Ice piers stabilize winter roads in shallow areas
The first set of ice piers were installed in the Fall of 2016, prior to the season freeze-up. Al Fitzgerald, National Practice Leader for Ice Engineering, says, “Due to the overwhelming success of the pilot ice piers, in 2017 we installed additional piers in two other problem areas. During the 2018 winter road season, all sites performed very well in eliminating the detrimental effects of washing. This success increases the mission assurance of the project, and eliminates the requirement for extensive repairs, as well as the cost of additional construction for bypass routes.”
The Winter Road Joint Venture is continuing to implement this solution at additional sites along the road, and will be installing piers in two supplementary locations in August 2018. Al advises, “The ice piers are expected to mitigate the negative impacts of severe weather fluctuations, by providing improved resilience to a major cause of winter road ice degradation.”