A remote monitoring system based on the global navigation satellite system was established at the Limin Tunnel portal of a high-speed railway to investigate the damage evolution of silty clay slopes in cold regions. Displacement, temperature, and soil moisture data were collected from four locations susceptible to instability. A discrete element model of the slope was established based on the measured data. Moreover, a coupled expansion method incorporating water-ice particle phase transition was used to analyze the microscopic damage characteristics, including surface displacement, particle interactions, and internal crack development. The results show that displacement variation is most pronounced during rapid freezing and fluctuating thawing phases, with the slope's toe experiencing more significant displacement than its crest. During rapid freezing, soil particle contact failure occurs when the bond strength between clay particles is insufficient to counteract the frost heave pressure. The development of cracks in the silty clay is rapid, with shear cracks accounting for 90.43% of the total.