Load Transfer of Piles Embedded in Ice-Poor Frozen Soils and Exposed to Varying Temperature

In recent years, cold regions have seen dramatic changes to the once-stable permafrost layers as a result of global warming. Changes in mean annual temperature directly impact the interaction between frozen ground and infrastructure systems such as piles and pipelines. Adfreeze, the controlling mechanism in a frozen soil–structure interface, is temperature dependent and weakens with rising temperature, while its cohesive nature may eventually change to a frictional one as pore ice turns into water. This paper studies the effect of temperature change on the behavior of steel piles in ice-poor soils subjected to pullout loading, especially during the transient melting state. A series of pullout pile load tests were carried out on a model steel pipe pile embedded in frozen sand and exposed to varying temperatures between $-{10}^{\circ }\mathrm{C}$ and 0°C. Strain-controlled pile load tests were performed to observe the pullout load transfer and failure mechanism of the pile, while constant-load tests were carried out to study the creep behavior of the pile exposed to different temperatures. Interface behavior was monitored by strain gauges and thermocouples mounted on the pile surface. Pullout capacities were found to vary linearly with temperature until entering the transient state near pore ice’s melting temperatures. Creep rates under constant loads increased with the rise in temperature which eventually resulted in accelerated tertiary creep in the near-melting temperatures. Stress profiles showed severe variation close to the soil surface while changing to an almost average constant value toward the tip of the pile. Investigating the behavioral change during the step-wise temperature rise revealed the characteristics of the transition from a frozen to unfrozen soil–structure interface.