Effects of Road Alignment and Fill Height on Transverse Thermal Asymmetry in a G219 Rock-Filled Ventilated Embankment

Road alignment creates unequal shortwave-radiation inputs on opposite embankment slopes, whereas the way in which overlying fill height redistributes this contrast among embankment layers remains unclear. This study aimed to quantify how road-axis azimuth controls transverse heat input and how upper fill height redistributes this input among the upper fill, rock-filled target layer, and permafrost foundation of a representative G219 rock-filled ventilated embankment. A two-dimensional transient enthalpy-based heat-transfer model, incorporating a smoothed phase-change treatment and coupled convection–shortwave boundary conditions, was used to compare three azimuths (0∘, 45∘, and 90∘), three upper fill heights (0.5, 1.5, and 3.5 m), and cold-year, reference-climate, and warm-year boundaries. Three counterfactual scenarios were used to separate the effects of target-layer equivalent thermal properties and exposed-surface optical conditions, while continuous simulations over 0∘–165∘ verified the representativeness of the formal azimuths. The common-domain response at 45∘ reached 67.9–70.1% of that at 90∘, indicating a continuous transition from near-symmetric to strong transverse heating input. Under the thermal–optical scenario at 90∘, increasing fill height increased common-domain asymmetry by factors of 2.69–2.89; however, the target-layer response consistently peaked at 1.5 m, whereas the foundation-layer response decreased. The upper-fill-to-target-layer peak lag also increased with fill height. These patterns persisted across climate boundaries and prescribed thermal–optical–conductivity perturbations. Within the controlled scenarios, road alignment set the transverse heat input, whereas fill height regulated its within-profile transfer and layer-specific thermal response. The results support comparative thermal assessment of embankments with a similar upper-fill–rock-filled-target-layer–permafrost-foundation sequence, rather than design of an optimum fill height for a specific site.