AUTC project number: 510011
Margaret Darrow (UAF)
US Department of Transportation (RITA)
A warming climate has been identified as unequivocal by the Intergovernmental Panel on Climate Change with greater and faster temperature increase demonstrated at northern latitudes, and with an overall increase in precipitation. Analysis of field data collected throughout the arctic and subarctic corroborates with these findings, demonstrating an overall warming of permafrost temperatures. As indicated by thermal modeling, the stability of permafrost� below roadway embankments is greatly affected by surface temperatures, thus, as climate warms, permafrost degradation represents a major issue for the design and maintenance of embankments. While the thermal stability of embankments in a warming climate has been investigated, the impact of groundwater and the effect of advective heat transfer on permafrost degradation below embankments has been overlooked. Recent studies indicate that groundwater flow along the permafrost table will cause permafrost degradation to occur one to several orders of magnitude faster than atmospheric warming alone. Thus, it is imperative for the long-term stability of infrastructure in permafrost regions that we better understand the complex interaction among groundwater, permafrost, and overlying embankments. The overall goal of this research is to develop a relationship among groundwater flow, permafrost degradation, and embankment stability. The completion of this study requires collaboration between researchers from the University of Alaska Fairbanks (UAF) and from the Université de Montréal (UdeM). Elements of this collaborative study include: field work at the Alaska Highway test section near Beaver Creek, YT, Canada, laboratory measurements of hydraulic conductivity and unfrozen water content, properties that are typically not measured for frozen soils due to inadequate laboratory resources, and modeling of the interaction among these complex phenomena, using coupled mathematical equations in the COMSOL Multiphysics software package. The numeric model that incorporates the measured data from the lab and field will be used to simulate the road embankment to determine the contribution of energy advection to the frozen ground via groundwater flow. The results of this study will facilitate a more complete understanding of groundwater flow through taliks and within warm (near 0°C) permafrost soils with high unfrozen water content, however, the model produced from this research is only the first step in understanding the complex interaction among embankments, groundwater flow, and permafrost. Additional data will further refine the model, eventually resulting in a powerful tool in the design of roadway embankments. It is expected that future phases of this research would yield highway specifications that would be further vetted as implemented experimental sections, and eventually developed into standard highway specifications. By better understanding these complex phenomena, we will be able to produce a new model that incorporates both conductive and advective heat transfer processes. Such a model is a prerequisite to the design of robust embankments and effective mitigation techniques to manage groundwater flow, eventually resulting in cost-savings in the maintenance of transportation infrastructure.