Experimental validation of passive permafrost cooling systems

In areas of warm permafrost, the thawing of interstitial ice in the permafrost layer can cause man-made infrastructure to suffer from thaw settlement damage and failure. For highway and railway embankments, thermosyphons and air convection embankment (ACE) layers are two methods that can be used to reduce embankment and foundation soil temperatures and prevent thaw settlement. These techniques utilize the low air temperature during winter to enhance freezing of the foundation soils and maintain the thermal integrity of the permafrost foundation. In the present paper we report on the application of these techniques in a full-scale field application, carried out as part of a new road building project near Fairbanks, Alaska. Three separate cooling techniques were utilized in the project, including hairpin thermosyphons, horizontal ACE layers, and ventilated shoulders in three different configurations. Each of the three configurations was instrumented with a thermal monitoring system in an effort to evaluate the cooling effectiveness and predict the long-term impact on underlying permafrost temperatures. This paper describes the cooling systems that were used in the project including the thermal monitoring system, and presents performance results for the first year of operation.