In order to investigate the frost-heaving characteristics of wintering foundation pits in the seasonal frozen ground area, an outdoor in-situ test of wintering foundation pits was carried out to study the changing rules of horizontal frost heave forces, vertical frost heave forces, vertical displacement, and horizontal displacement of the tops of the supporting piles under the effect of groundwater and natural winterization. Based on the monitoring condition data of the in-situ test and the data, a coupled numerical model integrating hydrothermal and mechanical interactions of the foundation pit, considering the groundwater level and phase change, was established and verified by numerical simulation. The research results show that in the silty clay-sandy soil strata with water replenishment conditions and the all-silty clay strata without water replenishment conditions, the horizontal frost heave force presents a distribution feature of being larger in the middle and smaller on both sides in the early stage of overwintering. With the extension of freezing time, the horizontal frost heave force distribution of silty clay-sand strata gradually changes from the initial form to the Z shape, while the all-silty clay strata maintain the original distribution characteristics unchanged. Meanwhile, the peak point of the horizontal frost heave force in the all-silty clay stratum will gradually shift downward during the overwintering process. This phenomenon corresponds to the stage when the horizontal displacement of the pile top enters a stable and fluctuating phase. Based on the monitoring conditions of the in-situ test, a numerical model of the hydro-thermo-mechanical coupling in the overwintering foundation pit was established, considering the effects of the groundwater level and ice-water phase change. The accuracy and reliability of the model were verified by comparison with the monitoring data of the in-situ test using FLAC3D finite element analysis software. The evolution of the horizontal frost heaving force of the overwintering foundation pit and the change rule of its distribution pattern under different groundwater level conditions are revealed. This research can provide a reference for the prevention of frost heave damage and safety design of foundation pit engineering in seasonal frozen soil areas.

A characteristic of frozen ground is a tendency to form banded sequences of particle-free ice lenses separated by layers of ice-infiltrated soil, which produce frost heave. In permafrost, the deformation of the ground surface caused by segregated ice harms engineering facilities and has considerable influences on regional hydrology, ecology, and climate changes. For predicting the impacts of permafrost degradation under global warming and segregated ice transformation on engineering and environmental, establishing appropriate mathematical models to describe water migration and ice behavior in frozen soil is necessary. This requires an essential understanding of water migration and segregated ice formation in frozen ground. This article reviewed mechanisms of water migration and ice formation in frozen soils and their model construction and introduced the effects of segregated ice on the permafrost environment included landforms, regional hydrological patterns, and ecosystems. Currently, the soil water potential has been widely accepted to characterize the energy state of liquid water, to further study the direction and water flux of water moisture migration. Models aimed to describe the dynamics of ice formation have successfully predicted the macroscopic processes of segregated ice, such as the rigid ice model and segregation potential model, which has been widely used and further developed. However, some difficulties to describe their theoretical basis of microscope physics still need further study. Besides, how to describe the ice lens in the landscape models is another interesting challenge that helps to understand the interaction between soil ice segregation and the permafrost environment. In the final of this review, some concerns overlooked by current research have been summarized which should be the central focus in future study.