A cast-in-place pile foundation, widely utilized in the permafrost regions of the Qinghai-Tibet Plateau, boasts superior load-bearing capacity, effectively mitigating the seasonal freeze-thaw effects. In permafrost regions, substantial pile foundation load-bearing capacity is provided by freezing strength, with the freezing strength determined by the temperature of the surrounding permafrost. In modern times, global warming has been causing permafrost degradation, posing a risk to the safety of existing pile foundations. In order to maintain the stability of these foundations, it is crucial to release excess ground heat, considering the temperature-dependent freezing strength of the ground to pile shaft. Two-phase closed thermosyphons (TPCTs) have demonstrated strong performance in the realm of cooling permafrost engineering. In this study, TPCTs were utilized to mitigate the impact of permafrost degradation by installing them around a concrete pile in order to cool the foundation ground. Following this installation, a model experiment was carried out, which ingeniously focused on analyzing the cooling performance, the process of cold energy dissipation, and the cooling scope of the TPCT pile. The study's findings indicate that the operation time of the TPCT pile accounted for about 50% of the entire freeze-thaw cycle. This device could effectively cool the surrounding foundation soil within a specified area. The TPCT pile exhibited a low temperature advantage of 0.36 degrees C in comparison with the scenario without TPCT in terms of surrounding geotemperature, although it experienced significant cold energy dissipation. The conclusions drawn from this study have significant value for maintaining piles in permafrost regions.

Seasonal freeze-thaw (F-T) cycles significantly affect the mechanical properties of soils and the behavior of pile foundations in soils subjected to F-T cycles under different loading conditions. Soils exposed to F-T cycles can impact the performance of pile foundations. Consequently, the effects of F-T cycles should be taken into account when designing piles, particularly in cold regions such as Canada. In recent years, climatic conditions in Canada have changed due to global warming, increasing the number of F-T cycles in many regions each year. This study aimed to investigate the influence of different numbers of F-T cycles on the behavior of piles in sandy soils. Laboratory experiments were conducted on physical models of piles subjected to axial (uplift) and lateral loads combined with F-T cycles. The model was scaled using standard scaling principles, and the test apparatus was equipped with various sensors to measure temperatures, forces, and displacements. The results showed that as the number of F-T cycles increased, the lateral capacities of the piles under individual and combined loads increased steadily. The lateral load capacity increased from 350 to 430 N after five F-T cycles under individual loading and from 225 to 455 N after five F-T cycles under combined loading. However, the pile's uplift load capacity remained constant under individual and combined loads and there was no change due to F-T cycles. The results of this experimental study will be useful for understanding the behavior of piles subjected to seasonal F-T cycles and for improving the design of pile foundations in cold regions.

The warming and melting of permafrost due to climate warming pose a considerable threat to the integrity of the Pan Arctic building, thus jeopardizing sustainable development. The increase in ambient temperature in permafrost areas will cause deterioration in the bearing capacity of building pile foundations. Considering the continuous deepening of the active layer (za), the present paper used small-scale physical modeling to investigate the potential variation of bearing capacity and load transfer mechanism of pile foundations under the scenario of continuous degradation of permafrost. The ultimate bearing capacity of a single pile and the undrained shear strength of the ground under different za are estimated by cone penetration tests. In the static load test of single piles, the axial load-settlement, axial force of pile shaft, and earth pressure at the pile tip are measured. The results show that the rise in ground temperature and the deepening of the za shorten the elastic and elastic-plastic stages of the load-displacement curve, resulting in a gradual decline in the bearing capacity of a single pile. The pile-soil interface temperature is always higher than the adjacent ground temperature at the same depth. Adfreezing force of the pile-soil interface decreases due to the increase in ground temperature and water content. With the deepening of za, the peak point of the shaft resistance decreases from -30 cm to -60 cm under the ultimate state. Meanwhile, with more axial load transfer along the pile shaft to the pile tip, the share ratio of pile tip resistance to ultimate stress gradually increases. In addition, the temperature rise of frozen soil at the pile tip accelerates the settling rate of the pile, which eventually causes the pile foundation failure.

At present, the improvement of the horizontal bearing capacity of the piles by pre-consolidation of the soft soil foundation has been well recognized by practising engineers. However, how to estimate the increment of horizontal bearing capacity of piles during the pre-engineering process is still difficult. In this article, a practical calculation method for estimating the increment of horizontal bearing capacity of piles is established based on the Bowles[1] method and by considering the impact of pre-drainage and pre-consolidation treatment of the layered soft soil foundation. This method provides an effective way to calculate the shear strength index and pre-consolidation treatment time based on the shear strength of undisturbed soft soil by laboratory test. Meanwhile, the elastoplastic solution of the horizontally loaded pile and the calculation formula of the plastic zone depth of layered soft soil foundation are analytically derived, based on the influence of elastoplastic yielding of soils surrounding the pile. In addition, the source code for computing the horizontal displacement of the pile top and the maximum bending moment of the pile body are given. Finally, the horizontal displacement, bearing capacity and the maximum bending moment of piles in the sluice pile foundation engineering case in Zhejiang Province are calculated according to the proposed method. The results of the field tests before and after the pre-consolidation treatments are compared. It is found that the estimated results are close to the test results, which may provide a good reference for similar engineering designs.