Rationalizing the Design of Adfreeze Piles with Limit States Design

ABSTRACT: Adfreeze steel pipe piles (adfreeze piles) are a commonly used foundation type in permafrost areas and are well suited to relatively light loads. The strength of the permafrost into which the piles are installed is time-dependent. Permafrost has higher resistance to short-term loads than sustained loads, all else being equal. Adfreeze piles are designed by assuming that they will settle in creep under load, over the life of the structure being supported. The capacity of adfreeze piles is dependent on the pile configuration, the nature of the load being applied, the characteristics of the permafrost, and the allowable deformation of the structure being supported. Pile capacity can be optimized by taking into account the duration of the various types of loading be imposed on the pile. It is proposed that this be done by considering long-term and short-term loading separately. In the context of Limit States Design, allowing for deformation is analogous to Serviceability Limit State (SLS). It is not practical to think of adfreeze pile capacity in terms of an Ultimate Limit State (ULS). Consequently, it is proposed that piles should be designed by referencing service (unfactored) loads, as designing for factored loads may be unnecessarily conservative. An approach to maintaining appropriate conservatism under SLS is proposed. Compression loading and frost-jacking resistance are considered.