Three-Dimensional Geocryological Modeling of a Road Embankment–Foundation System Under Permafrost Degradation: A Case Study of the Nadym–Salekhard Highway, Yamalo-Nenets Autonomous Okrug, Russia

Transport infrastructure in the Arctic designed on the principle of preserving the frozen state of foundation soils is increasingly affected by climate warming. Degradation of permafrost beneath embankments is aggravated by anthropogenic factors, such as inadequate drainage, disturbance of the snow cover and asymmetric insolation of slopes of opposite exposure. This paper presents a three-dimensional geocryological model of the embankment–foundation system of a section of the Nadym–Salekhard highway (Yamalo-Nenets Autonomous Okrug, Russia) and a long-term forecast of the permafrost-table position. The requirements for software capable of simulating thermophysical processes in cryogenic soils were formulated, and the finite-element package Frost 3D was selected. The model incorporates the lithological structure, microrelief, spatially variable snow accumulation, wind regime, surface water in thermokarst depressions, phase transitions, moisture transfer and insolation with allowance for solar motion. The model was validated against a one-year engineering-geocryological monitoring programme with borehole thermometry to a depth of 10 m: the mean absolute deviation between calculated and measured temperatures is 0.06–0.10 °C. The forecast to 2033 under the SSP5-8.5 scenario indicates a lowering of the permafrost table by 3.5–4.2 m at the slope toes and the initiation of taliks in previously stable areas of the right-of-way. The results identify the time window within which adaptation measures remain technically effective and support the transition from passive preservation of frozen ground to active adaptation of the structure.