摘要：研究目的：对于半幅铺盖法地铁车站基坑，中立柱作为其特有的支护结构，直接影响着施工安全，但中立柱变形 规律复杂，在黄土地区对其还缺乏系统认识。本文以西安黄土地区首个半幅铺盖法地铁车站基坑为工 程背景，对中立柱的变形机理及变形规律进行研究，以期为该施工工法条件下黄土地区车站基坑围护 结构设计提供参考。研究结论： (1)中立柱的变形主要受基坑降水、车辆荷载、盖板及支撑自重、结构自重和坑底土体隆起影响，其中 坑底土体隆起影响最为显著；(2)中立柱累计变形可以分为微小下沉阶段、连续上升阶段、下沉阶段和 稳定阶段四个阶段，其中最大值发生在第二阶段；(3)中立柱隆起值随着土方开挖深度的增加而增大， 因此设计时必须考虑中立柱隆起问题，确保中立柱具有足够长度；（4）采用钢筋混凝土支撑加路面板 组成的临时路面系统和分八步实施的施工工序，可使中立柱沉降值在安全范围内；(5)该车站采用的施 工方法和支护结构的各种设计参数可为以后黄土地区类似地铁车站基坑工程提供参考。

Abstract：Research purposes： The center pillar is regarded as a particular support structure for the foundation pit of metro station using semi-covered excavation method, which can directly affect the safe construction, the deformation law of which is sophisticated, about which there are little experience and knowledge especially in loess area. This paper takes the foundation pit of metro station excavated firstly by semi-covered method in Xi'an as study background, studies deformation mechanism and deformation law of center pillar, so as to provide reference for the design of foundation pit retaining structure in the loess area on this condition.  Research conclusions： (1) The deformation of center pillar is relevant with the following factors, foundation pit precipitation, vehicle loading, weight of cover plate and support structure and heave of the bottom soil, in which the last factor has the greatest influence on deformation of center pillar. (2) The accumulative deformation of center pillar in real-time can be divided into four phases with little dropping phase, continuous phase, dropping phase and stable phase where the maximum occurs in the second stage. (3) The value of uplift of center pillar is increased with the addition of excavation depth. Therefore, the design must consider uplift problem of center pillar, to ensure that has a sufficient length. (4) The use of temporary pavement system composed of reinforced concrete support and pavement slab and the implementation of the eight steps of the construction process can make the deformation of center pillar safe. (5)The  construction method of this metro station and various design parameters of support structure can provide reference to similar projects in loess area. 