Cumulative frost heave and hydrothermal process of the high-speed railway subgrade under extreme climate conditions in northwest China

Abstract

The mechanisms underlying the long-term deformation response and hydrothermal processes of high-speed railway subgrades in high altitude, seasonally frozen regions remain poorly understood, especially under extreme weather conditions. This study, based on an eight-year continuous field monitoring of the Lanzhou-Xinjiang High-Speed Railway (LXHR), presents several novel findings. From 2015 to 2022, air temperature, ground surface temperature, and subgrade surface temperature consistently increased, while the average annual rainfall showed a decreasing trend. During this period, sporadic heavy rainfall events occurred, and the climate demonstrated anomalous fluctuations. Such occasional heavy rainfall can cause a rise in the groundwater table, leading to an increase in frost heave within the subgrade. Given the same climatic conditions, embankments display a greater frozen depth compared to road cuts, but experience relatively less frost heave. Frost heave deformation within the subgrade comprises two components: residual deformation and inherent frost heave deformation. Residual deformation primarily contributes to the annual cumulative increase in frost heave, a process succinctly described as the transportation and deposition of fine particles (less than 2 mm in diameter) in coarse fillers by water, in close proximity to the frozen edge, ranging from 0.8 m to 1.2 m of the subgrade. In summary, the results of this study serve as a reminder for engineering designers and researchers to give more attention influence of residual deformation and the current climate change, in consideration of the stability and long-term service performance of subgrade under extreme weather conditions in the future.