Air-Ducted Hangar Foundations at Thule, Greenland

Kevin Bjella

Dans les comptes rendus d’articles de la conférence: GEO2010 Calgary: 63rd Canadian Geotechnical Conference & 6th Canadian Permafrost Conference

Session: W2-C

ABSTRACT: d Hangar Foundations at Thule, Greenland Kevin Bjella, P.E. Cold Regions Research and Engineering Laboratory, Ft. Wainwright, Alaska, USA ABSTRACT The late 1940's and early 1950's was a pivotal era for permafrost engineering as studies of the fundamentals paved the way for new concepts in design and advances in technology. The United States air base at Thule, Greenland was originally constructed in 1951 and incorporated some of those advances, most notably the air-ducted foundation. More than 50 years have now passed offering an opportunity to critique this design and compare to the current engineering methodology. Also the unforeseen problem with ground water infiltration is discussed.

RÉSUMÉ: Les études fondamentales réalisées en ingénierie nordique à la fin des années 1940 et au début des années 1950 ont pavé la voie pour le développement de nouveaux concepts et de nouvelles technologies adaptés aux régions froides. Par exemple, lors de la construction en 1951 de la base aérienne américaine à Thulé au Groenland, certaines de ces technologies, dont notamment les fondations ventilées en hiver pour maintenir froid le pergélisol sous les infrastructures, ont été intégrées dès le départ dans la conception et la construction des bâtiments militaires. Plus de 50 ans après la construction de cette base militaire, l'analyse de la performance des fondations ventilées et sa comparaison aux méthodes actuelles en ingénierie nordique permettent de tirer des leçons utiles au domaine. Les problèmes associés aux fondations ventilées et à la dégradation du pergélisol sous les infrastructures sont aussi présentés et discutés. 1 INTRODUCTION Thule Air Base is located in Northwest Greenland (N 76° 32', W 68° 45') on an ice free margin between the Greenland Ice Cap and the waters of North Star Bay (Figure 1). This region consists of permanently frozen glacio-fluvial soils with an estimated thickness of approximately 350 m (Davies et al 1963). These soils contain massive ice in the form of ice wedges, segregated ice and relict ice (Corte 1962), and polygonal ground is visible throughout the area. Figure 1. Location and area map Thule, Greenland. The air base was constructed in 1951, and the foundation design for the structures incorporated the latest in permafrost engineering technology to insure that degradation of the massive ice and ice-rich soil did not occur. However, design inadequacies of the air-ducted systems have resulted in thaw settlement problems. This paper discusses the design, problems encountered, and advantages of this type of foundation. 1.1 Permafrost The permafrost soils of the Thule area are glacio-fluvial in origin, and are composed of glacial till, sand to cobble and boulder sized material, with occasional zones of finer grain silts and clays. They overlie an inclined sequence of shale and dolostones intermittently intruded by diorite rock. The thickness of the soil increases with proximity to the ice cap, and at the location of the airfield the thickness is 5 m to 10 m with some bedrock outcropping. Massive ice, in the form of ice wedges up to a meter wide and meters deep, are predominate in the area. The ice wedges extend laterally up to 5 m and form polygonal ground with high centers. The terrain in the immediate area of the base was highly disturbed during construction; however an isolated undisturbed location exists next to the airfield containing significant ice wedge surface expression, giving an indication of the amount of massive that exists elsewhere. Additionally, oblique aerial photography from prior to construction shows the entire airfield area to have consisted of polygonal ground. The top of the wedges are located at the bottom of the active layer which is from 30 cm to 100 cm in depth depending on soil type and vegetation. In locations were shallow bedrock exists, the wedges terminate at the soil bedrock interface. The active layer can be 2 m in depth under non-vegetated fill material. Also, a few isolated remnants of glacial ice buried and preserved have been found in the area (Corte 1962). Vegetated areas consists of lichens, moss, and cotton grass, and the climate of the area is high-arctic marine

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