Long-Term Evaluation of Permafrost Passive Cooling Features in Interior Alaska

In 2003, the Alaska Department of Transportation and Public Facilities began a new road building project near Fairbanks, Alaska. The project (now known as Thompson Drive) contains three different types of passive cooling systems aimed at maintaining the thermal stability of underlying permafrost. The cooling systems utilize air convection embankment layers, ventilated shoulders, and two-phase thermosyphons in three different configurations. Each of these systems provides a passive cooling effect by enhancing the winter-time cooling of the embankment and underlying foundation soils, thus helping to preserve underlying permafrost and maintain the structural integrity of the roadway. In this paper we provide a summary of the performance data for Thompson Drive over a 15-year period extending from 2005 to 2020. Each of the systems included in the project has demonstrated effective cooling of the underlying soil layers despite a string of very warm years (2014–2019) in the Fairbanks area. In the present paper we focus on the performance of Test section #1 of the project, which includes a combined system of hairpin thermosyphons and ventilated shoulders. Temperature time series for a number of key locations within the test section show the cooling progress during the test period. In addition, contour plots of mean yearly temperatures provide a spatial indication of the effectiveness of both the thermosyphon and ventilated shoulder features.