Centrifuge modelling of axially loaded steel piles in cold and thawing frozen sand

Foundations in northern climates are founded under ground conditions that are certain to change due to climate warming. Piled foundations situated in permafrost are designed to resist loads by mobilising the shaft friction from adfreeze strength that is attributed to the ice-soil bonds in contact with the pile. Design considers ground warming causing thawing over time and normally specifies a thermal condition whereby mitigation measures, such as thermosyphons, need to be implemented. While pile design and analysis for completely frozen and thawed profiles are defined in terms of pile capacity, the intermediate condition, during transition from frozen to thawed, is not well examined. In this study, centrifuge modelling is utilised to quantify the reduction in pile capacity and foundation stiffness under an axial monotonic loading as initially frozen sand profiles warm and thaw depth increases. The results show agreement between the physical models and analytical methods for piles in fully frozen and thawed ground. A marked decrease in pile capacity occurs as ground temperatures approach freezing and thaw depth increases. The results are the first comprehensive physical model testing programme aimed at quantifying pile performance in frozen and warming ground under field-realistic stress conditions.