Interface shear strength characteristics of steel piles in frozen clay under varying exposure temperature

The ultimate shaft capacity of pile foundations in frozen grounds has long been correlated to the long-term shear strength of the surrounding frozen soils using a surficial roughness factor "m". This roughness factor is different for different pile materials (e.g., steel, concrete, and timber), but is often assumed to be constant for any soil type, ground temperature, or stress condition. The current study evaluates the validity of the proposed roughness factor "m" for steel piles embedded in frozen clay and exposed to different scenarios of ground temperatures and normal stress levels. Interface element tests were utilized to characterize the shear strength of frozen Leda clay and the adfreeze strength of the pile-frozen clay interface and to investigate the proposed roughness factor "m" for steel piles exposed to various temperatures and normal stress conditions. The experiments were carried out in a walk-in temperature-controlled environmental chamber. Roughness factor "m" was found not to be a constant number for a given pile material, but rather to decrease with an increase in the freezing temperature. A frictional factor "n", analogous to roughness factor "m", was also introduced to correlate the frictional resistance of frozen soil to the frictional resistance of the pile-soil interface. A temperature-dependent empirical equation was also proposed for predicting the shaft capacity of steel piles based on the shear strength parameters of the surrounding ice-rich clay soil. (C) 2019 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society.