THERMAL REGIME OF HIGHWAY SUBGRADES IN SEASONAL FREEZING CONDITIONS OF NORTHERN KAZAKHSTAN

Abstract

This study examines the thermal regime of multilayer highway subgrades under seasonal freezing conditions in Northern Kazakhstan, with particular attention to differences between soil beneath the pavement and adjacent snow-covered ground. Field monitoring was conducted along the Kosshy highway near Astana using a vertical array of temperature and relative humidity sensors installed within pavement layers and the underlying soil profile. Measured temperature gradients were used to estimate the effective thermal conductivity of pavement layers and frozen subgrade soil through inverse calculations based on Fourier’s law. The results show that the multilayer pavement structure significantly modifies the thermal regime of the soil profile, producing steeper temperature gradients and deeper frost penetration compared with nearby snow-insulated ground. Moisture migration in the vapour phase was evaluated using a diffusion-based formulation derived from Fick’s law. In addition, a simplified energy-balance approach was applied to estimate the potential upper limit of vapour-related ice accumulation by relating conductive heat flux to latent heat associated with vapour deposition. The comparison of the pavement and snow-covered profiles demonstrates that differences in thermal conductivity and thermal boundary conditions strongly influence both temperature distribution and potential moisture redistribution in freezing soils.