A Case Study on Thermal Foundation Design for the Goldstream Valley Bridge - Alaska Railroad MP 432.1, west of Fairbanks, Alaska

摘要

This paper details the geotechnical and cold regions engineering associated with replacing Alaska Railroad Corporation's (ARRC's) Goldstream Valley Bridge; including discussion of past performance of the former bridge, subsurface investigations, and foundation design for supporting the new bridge on driven steel piles supplemented with passive refrigeration. The aging former bridge was performing poorly (although still under safe operation) due to degradation of the relatively warm permafrost, stream bank erosion and minor migration of the stream channel with time. ARRC proactively replaced the bridge with a new longer span that placed the new abutments beyond the ends of the former bridge, and installed a new pier near the apex of the thaw bulb (which, theoretically, is relatively symmetric with any potential continued lateral soil migration). The steel pile foundations for the new bridge are being passively cooled using thermosyphons, in order to limit further degradation of the permafrost around the support soils and aggrade frozen soils immediately surrounding the piles. The bridge was reconstructed in 2009/2010 and instrumentation has been installed to monitor thermal performance.