【摘要】 大断面渐变段城市地铁隧道具有跨度大、渐变段截面变化大和覆岩厚度薄等特点，是隧道工程重要风险源之一。本文以青岛地铁4号线暗挖区间渐变段地铁隧道施工为背景，结合现场监测数据，应用MIDAS GTS有限元数值模拟软件，对现场施工方案进行了优化。研究结果表明：现场施工方案存在施工作业面小和器械摆放不方便等缺点，并且在开挖过程中存在围岩变形欠稳定等情况，容易导致局部坍塌。通过优化施工方案，改变预留核心土的位置以及初支成环的顺序，使得拱顶稳定后竖向位移比优化前降低了45.16%,左右拱腰收敛稳定后水平位移分别比优化前降低了61.90%和32.59%,在确保围岩稳定性的同时，还有着施工作业面大和器械摆放方便等优点，可为类似工程提供借鉴。更多还原

【Abstract】 Urban subway tunnel with large section and gradual change is one of the important risk sources of tunnel engineering because of its large span, large cross-section variation and thin overburden thickness. Based on the background of the underground tunnel construction in the gradual change section of Qingdao Metro Line 4 and combined with the field monitoring data, the MIDAS GTS finite element numerical simulation software is used to optimize the field construction scheme. The results show that the site construction scheme has the disadvantages such as small construction surface and inconvenient equipment placement, and the surrounding rock deformation is not stable in the excavation process, which is easy to lead to local collapse. By optimizing the construction scheme and changing the position of the reserved core soil and the order of the initial supporting ring, the vertical displacement of the stabilized vault is reduced by 45.16% compared with that before optimization and the horizontal displacement of the left and right arch waist is reduced by 61.90% and 32.59% respectively compared with that before optimization. The optimization scheme ensures the stability of surrounding rock at the same time, and also has the advantages of large construction area and convenient placement of equipment, which could provide the reference for the similar projects.更多还原