With global warming and intensified rainfall, the heat and moisture transfer processes within frozen subgrades beneath asphalt pavements have become increasingly complex, posing risks to highway stability in cold regions. This study developed a multi-physics coupled indoor simulation system based on a typical asphalt highway structure on the Qinghai-Tibet Plateau to examine subgrade responses under solar radiation, wind, and rainfall. Results showed that rainfall shifted the dominant depth of moisture migration from 7 cm to 12 cm, with moisture at 2 cm and 7 cm increasing rapidly by 2.67 % and 1.58 %, respectively. A nonlinear decrease-increase pattern was observed at 12 cm due to the capillary barrier effect. Evaporative latent heat significantly suppressed surface warming, reducing the temperature rise at 2 cm by 59.2 %, and delayed heat transfer to deeper layers (reductions of 54.5 %-64.7 %). A cumulative heat flux prediction model, incorporating solar radiation, evaporation, convection, and surface wetting, showed high accuracy (R-2 = 0.981 and 0.952; relative errors: 4.1 % and 9.6 %). Sensitivity analysis identified the surface wetting rate coefficient (beta) and evaporation attenuation coefficient (gamma) as dominant factors (F > 6.0). These findings improve understanding of rainfall-induced thermal effects and offer guidance for climate-resilient road infrastructure in permafrost regions.

The real simulation of vehicle loads is the key to studying the dynamic behaviors of subgrade fill in cold regions. Considering the time interval between adjacent vehicles, a series of dynamic triaxial tests with continuous and intermittent cyclic loading were conducted. The results show that the intermittent effect of cyclic load can enhance the stiffness of frozen subgrade fill, which is also strengthened by the increasing intermittent stages and ratios. The initial dynamic shear modulus of frozen subgrade fill can be effectively described using a function that accounts for the intermittent stage and intermittent ratio. Furthermore, a relationship between the maximum shear stress and the initial dynamic shear modulus has been established. A modified HardinDrnevich model is proposed to consider the interaction between the dynamic shear modulus, the intermittent stage, and intermittent ratio. The damping ratio increases nonlinearly as the increasing dynamic shear strain and intermittent ratio. A shear strain threshold exists and is slightly affected by the intermittent stage, but it decreases with increasing intermittent ratio. When the dynamic shear strain is larger than the shear strain threshold, the damping ratio increases with the increase in intermittent stage. The research results can provide a guidance for further understanding of the dynamic properties of frozen subgrade fill under the actual vehicle loads.