Field Experimental Study on the Temperature and Humidity Field and Deformation Evolution Characteristics of a Cut-Fill Subgrade in a High-Altitude Loess Area

Loess subgrades are highly susceptible to hydro-mechanical degradation under the combined effects of rainfall and temperature variations, leading to reduced structural stability and threatening highway operational safety. This paper investigates a cut-fill loess subgrade along the G85 highway in Guyuan City, monitoring temperature-moisture variations and settlement characteristics from the completion of construction through two years of operation. The results indicate that seasonal temperature fluctuations are more pronounced in fill sections than in cut sections. The left highway shoulder and slope toe shows the highest sensitivity to environmental changes. The volumetric moisture content in the fill section exhibits seasonal variations, with sensitive areas concentrated near the top layer of the subgrade and the slope toe. Influenced by rainfall, snowmelt, and freeze-thaw cycles in winter and evaporation in summer, the volumetric moisture content fluctuates significantly. Infiltration and temperature changes trigger localized cracking, resulting in differential settlement and compromising slope stability. Subgrade settlement displays layered and differential characteristics. During construction, the settlement rate reached 0.56 mm/day in fill sections and 0.13 mm/day in cut sections. After March 2024, settlement rates across the entire section stabilized below 0.1 mm/day. This research provides academic guidance for the construction and operation of subgrades in loess areas.