Force and deformation characteristics of subway station foundation pit under severe cold conditions

Based on Hohhot Metro Line 1, a self-developed freeze-thaw cycle test device was used to conduct the laboratory test on the temperature distribution of foundation pit soil, the frost heaving amount of surface soil, and the stress and deformation characteristics of underground continuous wall, and the stress and deformation characteristics of the foundation pit under different wind speeds, water contents, and temperatures were analyzed by the numerical simulation. Analysis results show that the soil around the foundation pit exhibits bidirectional freezing characteristic during the cooling process from 5 ℃ to -30 ℃, and the maximum freezing depth near the underground continuous wall can reach 18.2 m (the bottom of the foundation pit downward 1.09 m). The maximum deformations of foundation pit soil and underground continuous wall increase with the increase in the freeze-thaw cycles and tends to be stable in six freeze-thaw cycles. The maximum surface uplift during the last freeze-thaw cycle can reach 3.85 times that during the first freeze-thaw cycle. The horizontal frost heaving force is approximately parabolic in distribution along the underground continuous wall. The maximum frost heaving force appears in the middle of the underground continuous wall and can reach 775.8 kPa at -30 ℃. Wind speed has a significant effect on the heat exchange of foundation pit soil. The horizontal earth pressure of the foundation pit is linearly correlated with the wind speed of 0-0.4 m·s^-1. The earth pressure fluctuates and increases with the wind speed of 0.4-2.5 m·s^-1. When the wind speed is greater than 2.5 m·s^-1, the earth pressure is basically stable. When the wind speed is 0-0.4 m·s^-1, the surface deformation is linearly correlated with the wind speed. When the wind speed is 0.4-2.5 m·s^-1, the deformation increases step by step. When the wind speed is greater than 2.5 m·s^-1, the deformation is basically stable. When the water content increases from 13.3% to 33.3%, the maximum horizontal earth pressure increases by 44.2%. Under different constant negative temperatures, lower ambient temperature indicates that the maximum horizontal frost heaving force is closer to the bottom of the foundation pit. At -30 ℃, the maximum horizontal frost heaving force can reach 0.95 MPa, and the maximum surface deformation can reach 56.6 mm.