Experimental Study on Soil Temperature and Deformation during an Artificial Ground-Freezing Process Considering Interface Differences

Abstract

Artificial ground freezing (AGF) is prevalently employed in the construction of tunnel connecting passages. The soil heat transfer process plays a pivotal role in temperature alterations during freezing, subsequently influencing soil deformation and displacement and introducing uncertainties to the construction and safety. This study undertook indoor experiments to explore the freeze–thaw process of AGF within silty soft soil and explored the influence of interface disparities on soil heat transfer and deformation. The freeze–thaw model consisted of Hangzhou silty soft soil and a similarity tunnel model, subjected to freeze–thaw cycles at −18°C. To account for the freeze–thaw uncertainties stemming from interface differences, three external interfaces, namely, air–soil, steel–soil, and insulated steel–soil, were designated following engineering practices. By monitoring soil temperature and displacement, the analysis of soil heat transfer and deformation was conducted. The findings reveal that the external interfaces led to a reduction in the freezing rate and an elevation in the stable freezing temperature of the adjacent soil. Among them, the air–soil interface exhibited the most limited influence range, while the steel–soil interface had the most profound impact. The maximum freezing time of the soil corresponding to the steel–soil interface was prolonged by 355%, and the frozen soil temperature rose by 29% to 58%. Soil deformation was found to be closely associated with the temperature change process. The stable freezing temperature and frost heave displacement were significantly correlated with the freezing time and were effectively represented by the proposed statistical regression formula. The pronounced temperature gradient in the soil caused by the air–soil interface and steel–soil interface during thawing was identified as the primary cause for the increase in thaw settlement displacement. These results provide a valuable reference for ensuring the stability of soil during the construction of AGF connecting passages. Artificial freezing technology is often used to provide temporary excavation support for powdery silty soft soil during the construction of tunnel connecting passages. However, the heat exchange caused by the interface between frozen soil and the surrounding environment leads to changes in the temperature field of the soil, which in turn affects the stability of the entire frozen soil structure. This study considers the influences of three common environmental interfaces during frozen excavation of tunnel connecting passages to the temperature development and deformation process of soil. Different interfaces have varying degrees of impact on the temperature changes during freezing and thawing processes, further causing soil deformation. Neglecting the temperature and deformation effects caused by environmental interfaces may pose significant safety hazards to the construction process, seriously affect the construction progress, and bring significant financial risks to the construction organization. Therefore, the construction organization should carefully consider the influence of interface effects to determine appropriate freezing schemes and safety measures. In addition, the regression formula for soil freezing temperature, frost heave displacement, and freezing time can predict soil deformation, which helps prevent soil settlement risks in advance and ensure soil stability and the smooth progress of the project.