Field observations of a large diameter chilled pipeline experiment, Fairbanks, Alaska

Abstract

A large scale 105 m long, 0.9 m diameter chilled pipeline experiment was conducted to assess the response of a chilled pipeline that transitions between unfrozen and permafrost soils in discontinuous permafrost regions. Thermal and heave characteristics of the experiment for a three year monitoring period are reported. In response to the chilled pipeline, the progressive cooling patterns within the permafrost and unfrozen soils were different resulting in the development of a thermal boundary at the transition zone between the two thermally different soils. The absolute maximum heave was 0.197 m near the thermal boundary, resulting in a differential heave of 0.148 m. Three distinct heave phases were identified within the unfrozen soil. Phase 1 heave was characterized by rapid frost penetration, heave due to pore water expansion, and FHR between 2.9% and 4.8%. Phase 2 heave was characterized by ice segregation, occurred approximately between 1.0 m and 2.5 m below the pipeline, and FHR values were 9.6% to 9.9%. Phase 3 heave occurred below 2.5 m, was representative of pore water expansion, with FHR approximately 4%. The average FHR ranged between 5.4% and 6.8%.