Degradation characteristics and bearing capacity model of pile in degraded permafrost

Abstract

Global warming has led to increasing pile foundation deterioration in permafrost regions. Theoretical analysis and indoor model tests were used to analyse variations in the shaft resistance and ultimate bearing capacity (UBC) for various permafrost active-layer thicknesses (Za). A relationship for atmospheric temperature, Za and ground temperature was developed. The equivalent adfreezing force was used as an index to evaluate the degradation of pile foundation bearing behaviour and a theoretical model was established. Based on the theoretical degradation model and indoor experimental data, a model was established to reflect the deterioration of pile foundation bearing behaviour in warm permafrost regions. The model was verified using numerical simulations. The results showed that shaft resistance at the ultimate state can be divided into three stages (stable change, rapid increase and attenuation). The depth of the maximum values decreased from −0.40 m to −0.65 m with an increase in Za. The pile head load (Q) against pile head settlement (S) curves were divided into three stages (elastic stage, elastic–plastic and plastic). A greater Za made the plastic stage of the Q–S relationship occur earlier, resulting in a gradual decrease in UBC. The degradation variable (D) of bearing behaviour showed rapidly and then slowly increasing deterioration. This study provides experimental support for clarifying the degradation mechanism of pile foundation bearing behaviour and a degradation model to consider and quantify the impact of climate change on pile foundations in degraded permafrost.