A medium to long-term variations in hydrothermal process and deformation of high-speed railway subgrade in high-altitude cold region, Northwest China

Abstract

The issue of frost heave in high-speed railway subgrades located in areas with seasonally frozen soil is a significant concern that impacts both speed and safety, particularly during extreme weather conditions at high altitudes. This research focuses on the Menyuan section of Lanzhou-Xinjiang high-speed railway, where the average altitude is 3400 m and deep seasonal frozen soil exists. Based on field monitoring the temperature, moisture, and deformation of subgrade with coarse particle filler from 2015 to 2022, the research investigates the hydrothermal process of subgrade during freeze-thaw, examines the impact of climate change on frozen depth, and analyzes delamination frost heave. The results show that (1) the annual lowest temperature has a direct impact on frozen depth, which has varied greatly in recent years. The subgrade water content exerts an influence on frozen depth, with most subgrade frozen depth measuring approximately 2.5 m and reaching up to 3.0 m under extreme conditions; (2) By utilizing a waterproof composite geomembrane as an interface, the upper and lower portions of the subgrade can be simplified into two distinct frost heave systems: one without water supply and another with water supply. (3) The frost heave mainly occurs in the depth of 0.7 m to 1.5 m, and the frozen edge appears in the depth of 1.0 m to 1.5 m; (4) The amount of frost heave has a cumulative increasing trend, and the highest frost heave ratio is in the depth of 0.7 m to 1.5 m, followed by the depth of 0 m to 0.7 m, and the depth of 1.5 m to 2.7 m is the least. The findings of this study hold practical significance for enhancing the frost heave mechanism and modifying prediction methods. They also serve as a reference for optimizing the structure, disease prevention, filling selection, and gradation optimization of high-speed railway subgrade in seasonally frozen regions.