A closed-system unidirectional freezing experiment is conducted on the sandy silt found at the entrance and exit portal of the shield tunnel in Tianjin Metro. The test aims to investigate the temperature variation and frost heave deformation characteristics of frozen specimens under different freezing temperatures and moisture contents. Additionally, a numerical simulation of the unidirectional freezing process of sandy silt is performed using ANSYS finite element software. The test results indicate that: The higher initial moisture content in the soil, the longer duration of the stable freezing stage, and the initial freezing temperature of sandy silt increase with the increase of soil moisture content. Under the closed unidirectional freezing condition, the frost heave of the soil significantly grows with the increase of moisture content, while the influence of lower freezing temperatures on the final frost heave is relatively small. The simulated temperature variation trend corresponds well with the laboratory test results, except for an obvious mutation from the stable freezing stage to the slow cooling stage. As the freezing time progresses, the vertical frost heave increases at different depths within the soil. A more significant vertical displacement can be observed closer to the upper surface soil layer. After freezing for 500 minutes, the vertical frost heave displacement at different positions of the soil is linearly related to its depth.