Investigating the Effects of Groundwater Flow on the Thermal Stability of Embankments over Permafrost

Degrading permafrost below roadway embankments is a widespread problem in the north. Thermal modeling can help to determine thermally stable embankment configurations; however, this modeling typically does not include the effects of groundwater flow on the geosystem, which will cause permafrost degradation to occur faster than atmospheric warming alone. As part of a larger, ongoing research project, we present preliminary results of heat transfer modeling for an Alaska Highway test section near Beaver Creek, Yukon Territory, Canada. This experimental highway test section is located in an area characterized by muskeg vegetation underlain by ice-rich permafrost. While the overall project includes field work and laboratory measurements, this paper focuses on the results of exploratory modeling. A two-dimensional finite element program capable of mathematically coupling both heat and groundwater flow was used for modeling. Comparing model results produced using conductive heat flow only to model results using both heat and groundwater flow (heat advection) indicates that groundwater has a significant effect on the configuration of the thaw bulb and the temperature distribution within and below the roadway embankment. For example, using 50-year model results, including groundwater flow increases modeled thaw depths below the embankment by approximately 8 m, and can increase temperatures to an excess of +2.5°C at the bottom of the embankment. For wet terrain conditions, these preliminary modeling results indicate that it is essential to incorporate groundwater flow into thermal modeling, in order to understand better the complex interactions between roadway embankments and underlying permafrost.