Adfreeze Pile Design for Bridges along the Inuvik to Tuktoyaktuk Highway, Northwest Territories

摘要

The Inuvik to Tuktoyaktuk Highway includes eight bridges. The 140 km route is underlain by continuous permafrost, much of it ice-rich. Bedrock is generally too deep to be accessed for foundation construction. Mean annual ground temperatures ranged from about -1.8℃ to -4.3℃ near proposed bridge locations. Adfreeze steel pipe piles, which are generally suited to relatively light sustained loads, were selected as the foundation type for the bridges. Bridge loads tend not to be light and there is not much precedent for the use of adfreeze piles as bridge foundations. There were two particular challenges for the pile designs in this application. Firstly, the strength of permafrost is time-dependent. Adfreeze piles are designed by assuming they will settle in creep under load. For these bridges, traffic live load was a high proportion of the overall foundation load. Permafrost has higher resistance to short-term loads than sustained loads, all else being equal. The short duration of individual traffic load events was considered to justify correspondingly high capacities for traffic loading. Second, the bridges are required to have a 75 year design life. Warming of the permafrost is anticipated in response to predicted climate warming. It is likely that at least some of the permafrost will approach the onset of thaw over the design life of the bridges. A strategy is being implemented to monitor ground temperature response and implement mitigative measures, if pile capacity is determined to be compromised in the future. This paper describes the design rationale, including an adaptive response to climate change using thermosyphons.