针对高地应力软岩隧道开挖时围岩大变形问题，以某隧道圆形扩挖段为背景，采用三台阶法施工和3层初期支护+小导管注浆+二次衬砌的复合结构支护，并通过现场监测、数值模拟和理论计算研究开挖过程中的围岩变形及支护结构受力。结果表明：上、中台阶开挖时的隧道围岩变形速率较大，在仰拱封闭和第3层初期支护施作完成后，隧道变形趋于稳定；采用3层初期支护结构可有效改善隧道周边围岩应力，3层初期支护基本都是受压结构，拱腰和边墙处竖向应力最大，拱顶处水平应力最大；二次衬砌拱腰、拱顶、拱脚和边墙处安全系数均大于规范要求，保证隧道结构安全。

Large deformation often occurrs in soft rock tunnel with high ground stress during construction. Threebench excavation method and composite support structure of 3 layers of primary support + grouting through small duct + secondary lining are used to control large deformation of a soft rock tunnel with high ground stress. The mechanical characteristics of surrounding rock deformation and supporting structure are studied by site monitoring，numerical simulation and theoretical calculation. The results show that: 1) The deformation speed of surrounding rock is large when excavating top heading and intermediate bench; the deformation of surrounding rock becomes stable after construction of invert arch closure and the third primary support. 2) The stress of surrounding rock can be improved effectively by 3 layers of primary support; and the primary support structures are under compressive stress; the maximum vertical stress occurs in haunches and sidewall and the maximum horizontal stress occurs in crown top. 3) The safety factor of secondary lining can meet the requirements of related specifications and guarantee the safety of tunnel. 