Stability Challenge for a Wharf in the High Arctic

The Nanisivik Naval Facility is a proposed ship refueling station at Nanisivik, in the Nunavut territory of the Canadian Arctic. Nanisivik is the site of a former lead-zinc mine built in the mid 1970's with the support of the Canadian Federal Government by financing portions of the infrastructure, which included the deep sea wharf. With the mine now being decommissioned, the Federal Government intends to reuse the port site, including the wharf. Surveying during a 2010 inspection at Nanisivik indicated that the wharf had settled 2 metres since original construction. Borehole data collected in 2010, along with historical geotechnical data, left engineers searching for plausible ways to explain why the structure had settled so much. Historic surveys conducted by the government, and the 2010 survey, suggested that the settlement of the wharf was continuing, potentially at a linear rate. Regular storm wave overtopping of the wharf requires that the settlement problem be addressed if the facility is to be serviceable for a further 50 years. A second drilling campaign, undertaken in 2011 to depths much deeper than any previous drilling, encountered a deep, thick, permafrost clay layer. This clay is believed to be the primary contributor to the movement of the wharf. The preferred method to reduce the movement is to decrease the permafrost temperature through the use of deep thermosyphons. This paper discusses the history of the site, the investigations, and the options considered to address further settlement of the structure.