Qualitative evaluation of thaw settlement potential in permafrost regions of Canada

Abstract

Permafrost thaw negatively impacts the built environment in circumpolar regions. Thaw-induced settlement causes various engineering problems such as differential settlement, sinkholes, culvert failures, and pipeline deformations. Large-scale pre-construction evaluation reduces the risk of building infrastructure in thaw settlement-prone areas. This evaluation enables the comparison and screening of multiple route/location alternatives, the identification of vulnerable sections of a route, and the development of more effective site investigation plans. This study presents a systematic approach for evaluating thaw settlement potential in various regions across Canadian permafrost. In developing the approach, we considered three main factors: ground ice content, surficial deposit unit, and bedrock type. These factors were prioritized based on their relative importance in defining settlement behaviour, and a weighting factor was determined for each. In this study, the weighting factors of 0.78, 0.15, and 0.07 were suggested for ground ice content, surficial deposit type and bedrock type, respectively. We subsequently developed a Thaw Settlement Potential Index (TSPI), which can be calculated for any given location using publicly available Canada-wide resources. We calculated TSPI for several reported cases of thaw settlement issues across Canada and compared the results with site observations. A comparison was also made with a more detailed assessment conducted on the Northern Alaska Highway using a different approach. While the TSPI assessment required minimal time, effort, and resources, the obtained results generally matched those of finer-scale assessments with more detailed information. Thus, our methodology simplifies early identification of thaw-unstable regions in projects with large footprints and helps allocate resources more efficiently for subsequent site investigations.