Breaking New Ground – Using Fixed Snow Nets to Mitigate Avalanche Risk to the Trans-Canada Highway

Brian Gould, Cam Campbell, Andi Buechi

Dans les comptes rendus d’articles de la conférence: GeoOttawa 2017: 70th Canadian Geotechnical Conference; 12th joint with IAH-CNC

Session: Geohazards II - Rockslides and Avalanches

ABSTRACT: In British Columbia, the Trans-Canada Highway winds through the Glacier National Park and over Rogers Pass, which is a well-known area for snow avalanches. Each year avalanches affecting the highway disrupt the transportation of goods and people through this critical transportation corridor. Increasing traffic volumes and the mounting costs of closures to the economy has resulted in a need for new avalanche mitigation measures, including snow netting, which stabilizes the snow in the avalanche path start zone throughout winter. This mitigation measure has been specified for three avalanche paths near Rogers Pass. Even when snow-free, the site conditions are hazardous and complex and required expertise of engineering consultants, drilling experts, safety and helicopter logistics. To date this is the largest snow net project in the western hemisphere.

RÉSUMÉ: En Colombie-Britannique, l'autoroute transcanadienne traverse le Parc National des Glaciers et le Col Rogers, une zone connue pour les avalanches de neige. Chaque année, les avalanches affectant la route perturbent le transport de marchandises et de personnes à travers ce couloir de transport critique. L'augmentation des volumes de trafic et les coûts croissants des fermetures de l'économie ont entraîné la nécessité de nouvelles mesures d'atténuation des avalanches, y compris le déneigement, qui stabilise la neige dans la zone de démarrage de l'avalanche tout au long de l'hiver. Cette mesure d'atténuation a été spécifiée pour trois chemins d'avalanche près du col de Rogers. Même en cas de neige, les conditions du site sont dangereuses et complexes et nécessitent l'expertise des consultants en ingénierie, des experts en forage, de la sécurité et de la logistique des hélicoptères. À ce jour, c'est le plus grand projet de réseau de neige dans l'hémisphère occidental. 1. INTRODUCTION Snow avalanches are a significant natural hazard that affect a number of activities in mountainous regions of Canada and other alpine nations. In addition to affecting ski areas, mines, hydroelectric, and other industries, avalanches can disrupt the transportation of goods and people by impacting highways. When the Trans-Canada Highway opened in 1962, snow sheds and earthworks were constructed to protect travelers from the most frequent avalanche paths. These measures have since been supplemented by operational avalanche mitigation which incorporates temporary closures, and highway based Howitzers to trigger avalanches when the hazard is high. In recent years, increasing traffic volumes and decreasing tolerance for travel delays has led to a demand for more robust avalanche mitigation measures. New avalanche mitigations being installed in Glacier National Park will enhance Parks Canada™s successful avalanche control program using Howitzer fire that has been jointly operated with Canadian Armed Forces since 1962. One of these mitigation measures is snow netting, a form of supporting structure installed in avalanche starting zones that has been used extensively in Europe as well as other alpine regions. Recently, a large installation of snow nets was commissioned by Parks Canada in Glacier National Park to protect an exposed section of the Trans-Canada Highway (TCH) near Rogers Pass. The design-build project involved extremely challenging terrain, both from a design and installation perspective. This paper discusses the methodology used and presents some of the challenges encountered. 2. BACKGROUND ON SNOW NETS The idea of inhibiting the formation of avalanches in avalanche starting zones goes back more than a century (FAO 1985). Wooden stakes, stone walls and other landscape modifications were built to protect settlements, often after a historic avalanche event had occurred. Since the 1960s there have been significant advancements with snow-supporting structural systems (Figure 1), and in addition to protecting towns and villages, they have been used to protect ski areas, industrial sites, and transportation corridors.

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