为研究第三纪砂质黄土条件下的大断面隧道施工变形控制技术，以宝兰铁路大断面黄土隧道施工为依托，通过midas数值模拟软件对比分析不同仰拱封闭距离引起拱顶沉降实测数据，阐述大断面黄土隧道施工变形规律，以确定其合理的仰拱封闭距离为35 m；采用三台阶临时仰拱法，合理控制开挖步距： 上台阶为0.6 m，中台阶和下台阶为1.2 m； 辅以注浆小导管超前支护和锁脚锚杆加固等技术措施，达到了很好的变形控制效果，最大沉降控制为50~160 mm； 通过分析不同隧道断面净空变形规律，总结第三纪砂质黄土地质条件下，大断面黄土隧道施工预留变形量可取120~160 mm。

Sujiachuan tunnel on BaojiLanzhou railway is a large crosssection tunnel located in Tertiary sandy loess. The crown settlement under different distances between the tunnel face and the invert closing position is analyzed by means of “midas” program, the rule of the deformation of large crosssection loess tunnels in the process of construction is expounded and the appropriate distance between the tunnel face and the invert closing position is determined to be 35 m. The tunnel is constructed by top heading and twobench method, with temporary inverts installed, and the excavation cycle rate is controlled at 0.6 m in the top heading and 1.2 m in the benches. Forepoling and arch foot locking bolts are installed for the tunnel. In the end, good deformation control effect has been achieved, with the maximum settlement being control from 50 mm to 160 mm. Furthermore, the rule of the convergence of tunnels with different crosssections is analyzed and it is concluded that the value from 120 mm to 160 mm can be taken as the deformation allowance of large crosssection loess tunnels.