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.

Silty clay is widely distributed in seasonally frozen zones in China and frequently engages in engineering projects. Nevertheless, it exhibits significant frost susceptibility and generates substantial related freezing damage. To address this problem, this study investigates the impact of nano-zinc oxide (ZnO) on silty clay's frost heave characteristic. We conducted tests on silty clay with varying nano-ZnO contents, assessing plasticity limit, liquid limit, frost heave, and uniaxial compressive strength. The findings reveal that: (1) the addition of nano-ZnO can decrease the free water content, and result in both the plastic limit and the liquid limit increase, and further accelerate the freezing process, which is helpful to mitigate the frost heave caused by water migration; (2) the frost heave ratio decreases with increasing nano-ZnO content within the tested range, 4.0% addition of nano-ZnO can significantly reduce frost heave by 66.96%, and transform the silty clay from extreme frost heave to frost heave; (3) with the nano-ZnO content increases, the uniaxial compressive strengths of the specimen initially increases (0%-3.0%) and subsequently decreases (4.0%), and the brittleness also becomes more pronounced. According to the results of mechanical and frost heave tests, the optimal content of nano-ZnO is ascertained to be 3.0%. The results of this study provide a promising solution to mitigate the frost heave of silty clay, particularly in regions with limited coarse-grained soil.