Force and deformation characteristics of subway station foundation pit under severe cold conditions
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摘要: 以呼和浩特地铁1号线为依托，基于自主研发的冻融循环试验装置，针对基坑土体的温度分布、表面土体冻胀量、地下连续墙受力与变形特性进行室内试验，采用数值仿真分析了不同风速、含水率及温度下基坑的受力与变形特性。研究结果表明：基坑周围土体在从5 ℃到-30 ℃的降温过程中呈现双向冻结特征，靠近地下连续墙一定范围内土体最大冻结深度可达18.2 m(即基坑底面向下1.09 m)；基坑土体及地下连续墙的最大变形随着冻融循环次数的增加而增大，并在6个冻融循环周期内趋于稳定，末次冻融周期地表隆起量最大可达首次冻结时的3.85倍；水平冻胀力沿地下连续墙大致呈抛物线型分布，最大冻胀力出现在地下连续墙的中部，在-30 ℃时可达775.8 kPa；风速对基坑土体热交换有显著影响，在风速为0~0.4 m·s-1时风速和基坑水平土压力线性相关，风速为0.4~2.5 m·s-1时土压力波动增长，风速大于2.5 m·s-1后土压力基本稳定；在风速为0~0.4 m·s-1时风速和地表变形线性相关，风速为0.4~2.5 m·s-1时变形阶梯式增长，风速大于2.5 m·s-1后变形基本稳定；当含水率从13.3%提升至33.3%时最大水平土压力增加44.2%；在不同的恒定负温下，环境温度越低最大水平冻胀力的位置越靠近基坑底部，-30 ℃时最大水平冻胀力可达0.95 MPa，地表最大变形可达56.6 mm。Abstract: 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.
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图 15 风对基坑受力与变形的影响
Figure 15. Effects of wind on stress and deformation of foundation pit
图 16 不同风速下水平土压力的变化
Figure 16. Variations in horizontal earth pressure under different wind speeds
图 18 含水率对基坑冻胀的影响
Figure 18. Influences of water content on frost heave of foundation pit
图 20 温度对基坑冻胀变形的影响
Figure 20. Effects of temperature on frost heaving deformation of foundation pit
表 1 各物理量相似常数
Table 1. Similarity constants of each physical quantity
物理量 弹性、变形模量 均布面力荷载 应力 应变 泊松比 内摩擦角 线位移 相似常数 20 20 20 1 1 1 20 
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表 2 各层填土性质
Table 2. Natures of each layer of filling
层号 土类 高度/cm 密度/(g·cm-3) 质量/kg 面积/cm2 含水率/% 1 杂填土 6.5 1.7 107.4 1 000 3.0 2 素填土 11.0 1.9 209.2 1 000 5.8 3 黏性土 20.0 2.0 402.4 1 000 20.0 4 细砂 29.5 2.1 605.4 1 000 18.3 5 黏性土 30.0 2.0 588.6 1 000 27.0 6 细砂 15.0 2.1 307.8 1 000 18.3 7 黏性土 18.0 2.0 353.2 1 000 27.0
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表 3 水平冻胀力拟合方程
Table 3. Fitting equations of horizontal frost heaving force
温度/℃ y=Ax2+Bx+C A B C $-\frac{B}{2 A} $ -10 -0.002 0.177 0.201 53.832 -15 -0.003 0.339 -0.288 52.423 -20 -0.005 0.529 -0.271 51.755 -25 -0.008 0.806 -1.114 50.888 -30 -0.010 1.063 -1.824 50.935
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表 4 降温结束时模拟与试验的变形
Table 4. Deformations of simulation and test at end of cooling
mm 位置 P1 P2 P3 P4 P5 P6 P7 P8 P9 P10 试验 1.49 1.20 2.06 2.66 0.13 0.09 0.05 0.03 0.04 0.12 模拟 1.84 1.96 2.14 2.39 0.03 0.06 0.02 0.03 0.07 0.22
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