Tangential Heave Stress for the Design of Deep Foundations Revisited

Foundation structures in cold regions can be subjected to uplift forces, such as basal heave forces and tangential heave forces, that are caused by the freezing of frost-susceptible soils. Tangential heave force refers to the upward shear force that acts along the outer surface of the foundation after the adfreeze bond between the pile and soil is broken due to the frost heave of the soil. Deep foundations in cold regions need to be designed so that the shaft resistance provided by soils below the frost depth is greater than the tangential heave force induced by soils above the frost depth. The magnitude of the tangential heave force should typically be determined by multiplying the tangential heave stress by the outer surface area of the foundation within a frost depth. Therefore, tangential heave stress is one of the key parameters in design of deep foundations in cold regions. However, values of tangential heave stress reported in the literature show large variability. Part of this variability results from the conceptual confusion about the terms "tangential heave stress" and "adfreeze shear strength" and also from the different test methods and procedures used to measure tangential heave stress. This paper carefully reviews previous research on determination of tangential heave stress. The test procedures and methods are described and classified, and test conditions such as foundation material, soil type, frost depth, and ground temperature are described in detail when such data are available. Although some sources of the large variability in reported values of tangential heave stress can be resolved, more research is clearly needed to improve the fundamental understanding of ice-soil-foundation interactions.