Coupling effects of dynamic loading and freeze-thaw cycles on the thermo-hydro- deformational behavior of subgrade soils

Subgrade engineering in seasonal frozen ground regions frequently experiences subgrade and pavement damage in rutting regions under vehicle dynamic loads. To investigate the failure mechanism, we conducted laboratory tests with and without loading. Through experiments, this study investigates the internal thermal-hydraulic-deformation response mechanisms of soil under the combined effects of traffic dynamic loads and freeze-thaw cycle(FTC). Results indicate that dynamic loads first alter the soil's temperature field and pore water pressure(PWP) distribution: loads accelerate soil freezing and generate higher temperatures and more pronounced pore water pressure variations within the load-affected region. These alterations further drive moisture redistribution, manifested as enhanced upward migration during the early test period, ultimately forming high-water-content regions beneath the load. Spatial variations in moisture distribution directly induce differential displacement behavior: while dynamic loading promotes overall settlement stability, facilitating initial subgrade consolidation, locally concentrated moisture induced by loading increases the risk of uneven frost heave deformation. Additionally, during thawing, the high-temperature and high-water-content regions beneath the load become vulnerable zones prone to damage, failing first. This study elucidates the intrinsic relationship through which loading influences seasonal frozen ground subgrade deformation stability via the temperature-pore water pressure-moisture pathway, revealing the failure mechanism of subgrades in seasonal frozen ground regions under dynamic loading. It holds significant importance for elucidating the fundamental mechanisms of dynamic load-induced subgrade failures and formulating control measures.