Calculation method for ultimate support force of shield tunnel in homogeneous unsaturated clay strata
Article Text (Baidu Translation)
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摘要: 针对非饱和黏土地层盾构隧道极限支护力不易准确确定的难题,采用理论推导和工程算例分析相结合的方法系统研究了均质非饱和黏土地层盾构隧道开挖面支护力计算方法。考虑地层非垂直滑裂面形态、土体基质吸力作用、不完全土拱效应及主应力偏转特性,构建了考虑多因素耦合的竖向土压力解析模型;基于极限平衡楔形体模型,进一步推演构建了开挖面支护力计算方法;结合工程算例探讨了关键参数对支护力的影响规律。研究结果表明:土拱效应引发土体竖向应力非线性演化,随埋深增加呈现先陡增后增速趋缓规律;隧顶土体竖向应力与滑裂面角度、饱和度正相关,与黏聚力、拱顶位移负相关;高饱和度条件下,推荐计算方法与规范计算结果具有高度一致性,且二者所得结果均明显高于太沙基理论预测值,偏差幅度最高可达50%;随饱和度降低,推荐解渐趋接近太沙基理论解,饱和度变化引发的松动土压力波动幅度可达30%;开挖面极限支护力受内摩擦角、黏聚力及饱和度多参数耦合影响,其中地层饱和度为关键控制因素,其差异可导致支护力变化幅度超50%。Abstract: To accurately determine the ultimate support force of shield tunnels in unsaturated clay strata, a systematic study was conducted on the calculation method of support force at the excavation face of shield tunnels in homogeneous unsaturated clay strata by combining theoretical derivation and engineering case analysis. By considering the non-vertical slip surface morphology of the strata, the effect of soil matrix suction, the incomplete soil arching effect, and the characteristics of principal stress deflection, an analytical model of vertical earth pressure considering multi-factor coupling was constructed. Based on the limit equilibrium wedge model, a calculation method for the support force at the excavation face was further derived and constructed. The influence of key parameters on support force was discussed through engineering examples. The results indicate that the soil arching effect triggers a nonlinear evolution of vertical stress in the soil, showing a steep increase followed by a slower growth rate with increasing burial depth. The vertical stress at the top of the tunnel is positively correlated with the angle and saturation of the sliding surface and negatively correlated with the cohesive force and arch displacement. Under high saturation conditions, the recommended calculation method has a high degree of consistency with the standard calculation results, and both results are significantly higher than the predicted values of Terzaghi's theory, with a deviation range of up to 50%. As the saturation decreases, the recommended solution gradually approaches Terzaghi's theoretical solution, and the fluctuation amplitude of loose soil pressure caused by changes in saturation can reach 30%. The ultimate support force at the excavation face is influenced by the coupling of multiple parameters such as internal friction angle, cohesive force, and saturation. Among them, the saturation of the strata is the key controlling factor, and its difference can lead to a change in the support force value of more than 50%.
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