地铁车站基坑立柱隆起对混凝土支撑安全性的影响研究

Study on the Impact of Vertical Support Uplift on the Safety of Concrete Strut in Subway Station Excavation

摘要: 基坑内支撑支护体系中通常用立柱来保证内支撑的整体稳定性。本文研究了典型地铁基坑开挖过程中立柱隆起造成的混凝土支撑的弯矩以及对安全性的影响。首先结合结构力学计算模型提出了立柱临界隆起量的概念以及计算方法。并结合一个工程案例，讨论了边界条件和参数取值对临界隆起量计算分析结果的影响。结果表明，混凝土支撑中部的弯矩可用来计算临界隆起量、评估支撑的安全性。固接情况下的临界隆起量较小而竖向作用力较大，设计计算中建议采用固接分析的结果。采用短期刚度Bs替代弹性抗弯刚度EI计算得到的结果更为合理。计算结果与现场情况较为吻合，能够很好的解释现场部分混凝土支撑出现明显裂缝的现象。最后对立柱隆起控制措施也进行了探讨。

Abstract: In braced excavation, pillars are usually used as vertical supports to maintain the stability of the struts. In this paper, the bending moment and safety of concrete strut under the pillar uplift in subway station excavation are studied. The concept and analysis method of the ultimate uplift are presented. With a case study, the influence of boundary conditions and parameter values on the analysis results of the ultimate uplift is discussed. The bending moment at the middle of the pillar can be used to calculate the ultimate uplift and evaluate the safety of the strut. In the case of fixed ending, the critical uplift is smaller and the vertical force is larger. It is suggested to use the results of fixed ending model in the design. Using short-term stiffness Bs, instead of elastic bending stiff-ness EI, can give reasonable results. The calculation results are consistent with the field observa-tions, which can explain the obvious cracks on some concrete struts. Finally, the control measures of pillar uplift are also discussed.