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.

This study undertakes a comprehensive examination of the characteristics of the argillaceous, hard soil/soft rock (HSSR) lithology of the Unterangerberg formation in Tyrol, Austria, focusing on its swelling properties and anisotropic material behavior. The objective is to achieve an extensive material characterization to be able to calibrate material models accurately. This is to be achieved by means of an in-situ test campaign within the Angath adit tunnel construction site and accompanying laboratory tests. The geotechnical monitoring concept in a designated test gallery includes a chain inclinometer, extensometers, geodetic targets, shotcrete strain meters, photogrammetric observations, and a long-term irrigation test field, with a of the invert left exposed intentionally. The in-situ tests yield valuable insights into the intricate behavior of the HSSR lithology, offering a comprehensive description of material variability, and recommendations for characterization. Results indicate that despite the high swellable clay mineral content, significant swelling occurred only to a small extent during the observation period to date. The study concludes that the in-situ behavior of such formations significantly contributes to a better understanding of their characteristics, leading to a substantial reduction in critical load cases for future planning phases.