This study conducted load-bearing capacity tests to quantitatively analyze the impact of permafrost degradation on the vertical load-bearing capacity of railway bridge pile foundations. Meanwhile, a prediction model vertical load-bearing capacity for pile foundations considering permafrost degradation was developed and validated through these tests. The findings indicate that the permafrost degradation significantly influences both the failure patterns of the pile foundation and the surrounding soil. With the aggravation of permafrost degradation, damage to the pile foundation and the surrounding soil becomes more pronounced. Furthermore, permafrost degradation aggravates, both the vertical ultimate bearing capacity and maximum side friction resistance of pile foundations exhibit a significant downward trend. Under unfrozen soil conditions, the vertical ultimate bearing capacity of pile foundations is reduced to 20.1 % compared to when the permafrost thickness 160 cm, while the maximum side friction resistance drops to 13.2 %. However, permafrost degradation has minimal impact on the maximum end bearing capacity of pile foundations. Nevertheless, as permafrost degradation aggravates, the proportion of the maximum end bearing capacity attributed to pile foundations increases. Moreover, the rebound rate of pile foundations decreases with decreasing permafrost thickness. Finally, the results confirm that the proposed prediction model can demonstrates a satisfactory level of accuracy in forecasting the impact of permafrost degradation on the vertical load-bearing capacity of pile foundations.

Industrial by-products have a broad application prospect in sustainable soft soil treatment. The applicability and characteristics of a cement-slag-phosphogypsum based ternary cement (TC) are investigated for solidifying soft clay to create a crust layer. The strength and load-bearing behaviors of the solidified crust are characterized using unconfined compressive strength (UCS), triaxial compression, and small-scale loading tests. The ascending trends in UCS with increasing binder content (Cb) differ between TC solidified clay and cement solidified clay, and the UCS ratio between them increases with Cb. Besides, the failure strain and secant modulus of TC solidified clay have functional relationships with UCS, and the same functions work for cement solidified clay as well. In triaxial compression tests, the relationship curves of the deviatoric stress and excess pore water pressure with axial strain change to present more significant shear dilation characteristics as Cb rises from 6% to 8%, along with a sharp rise in the friction angle, suggesting the solidification performance improved to a higher level. The results of small-scale loading tests show that the ultimate bearing capacity (pu) increases with Cb and crust thickness (h), along with the potential crust failure mode transiting from punching to bending failure; the pu gets a sharp rise as Cb and h are just raised high enough to ensure the crust integrality. In more details, it is suggested to prioritize the effective solidification critical for stress spreading before enlarging h in order to achieve higher pu. Finally, TC has been applied and proven effective in engineering practice.