Pull-Out Capacity and Creep Behavior of Helical Piles in Frozen Ground

This paper presents pull-out capacity and creep behavior of a model helical pile and a model grouted shaft helical pile installed in frozen ice-rich silt in Gloucester, Ontario, Canada. The measured pull-out capacity of the model piles was compared to predicted capacities calculated using modified forms of previously published theoretical approaches based on the individual bearing model (IBM) and the cylindrical shear model (CSM). The modified IBM adequately captured the pull-out loading resistance of the helical pile; however, neither the modified IBM nor CSM could accurately predict the measured capacity of the grouted shaft helical pile in frozen ground. The creep behavior of the test piles in frozen soil was dependent on the applied creep stress and the frozen ground temperature. The pile creep rates increased when the ground exposure temperature increased, even under a constant creep loading condition. The pile creep rates measured in the current study were smaller compared to previously published results for similar stress and thermal boundary conditions. This could be attributed to creep rate hysteresis associated with ground warming, as well as the differences in the helix diameter. An improved graphical solution was also produced to predict creep rates for single-helix helical piles in frozen ground at various exposure temperatures. (c) 2020 American Society of Civil Engineers.