To investigate the temperature-field evolution and frost-heave suppression mechanism of cement-improved silty clay during underground shield docking, a case study is conducted on the underwater shield docking project of the Jiangyin-Jingjiang Yangtze River Tunnel. A large-scale three-dimensional loading physical model is constructed based on similarity criteria, and a comparative analysis is conducted on the temperature-field evolution, frozen-wall development, and spatiotemporal distribution of frost heave force between undisturbed silty clay and silty clay improved with 10% cement under asymmetric freezing conditions. Furthermore, the frost-heave suppression effect is quantitatively evaluated. The results show that the cement-improved ground has a lower cooling rate and a ~22.7% longer frozen-wall closure time than undisturbed soil. However, the development rate of the freezing front accelerates after closure, resulting in a significant reduction in the thickness difference between the frozen walls of the two soils after 90 days. Furthermore, the frost heave force exhibits a staged evolution during freezing: it increases significantly in the undisturbed soil before and after frozen-wall closure, whereas a noticeable lag is observed in the cement-improved soil, with a delayed peak occurrence. The maximum frost heave load is concentrated at the springline of the docking section. Specifically, the peak frost heave force in the undisturbed soil is more than double the initial ground pressure, whereas it decreases to 1.48 times the initial ground pressure after cement improvement. This corresponds to an average reduction of ~40% in the overall frost heave force, with a maximum suppression rate of 52% achieved in the central docking area. The cement improvement alters the thermophysical properties and moisture migration characteristics of the soil, influencing the evolution of the temperature field and frost heave force during freezing. Consequently, the frozen-wall formation process and frost heave response can be effectively regulated by appropriately designing cement improvement measures and dosages.