Abstract: This study focuses on permafrost degradation on the Qinghai-Xizang Plateau under warming and humidification. Using numerical simulations combined with geological surveys and environmental monitoring data from the G0615 Dema Expressway (Xiangride to Huashixia section), the research analyzes how water infiltration accelerates ground ice melting in silty clay layers and the evolution of hydrothermal states. The results indicate that underground ice melting occurs in four distinct stages: rapid temperature rise due to heat absorption by ice, stable temperature rise during the ice-water transition, rapid temperature rise of ice meltwater, and stable temperature rise of ice meltwater. Water infiltration significantly improves heat transfer efficiency at the ice-soil interface, leading to an initial increase followed by a decrease in the cooling range of surrounding soil. Additionally, higher infiltration rates cause the cooling range peak to occur earlier. Underground ice redirects water infiltration, but its melting gradually reduces the obstruction to seepage. For a constant cross-sectional area of ground ice, the time for complete melting decreases as it transitions from a vertical to a horizontal state. Horizontal ground ice melting exerts a greater influence on the temperature and seepage fields of surrounding soil, driven by factors such as hydration heat, ice-water transition, and dynamic infiltration path adjustments. This research offers a theoretical foundation for understanding the catastrophic melting of permafrost on the plateau under warming and humidification, supporting the development of more precise underground ice melting prediction models.

Key words: road engineering, numerical simulation, water infiltration, Qinghai-Xizang Plateau, permafrost degradation, underground ice