西格二线关角隧道浅埋砂层段施工技术及力学效应研究

关角隧道是西（宁）格（尔木）二线的控制性工程，在隧道入口处存在长约450 m的砂层，施工难度较大。由于在3台阶施工中出现了冒顶事故，故提出了4台阶施工的设想，并利用三维数值计算模拟了4台阶开挖支护过程，揭示了隧道的空间变形、地表沉降和初支受力特征。通过与3台阶施工模拟结果对比证实了4台阶方案的优越性；现场施工和变形量测结果表明，采用大拱脚断面形式和超短四台阶施工方案，施作长大水平超前管棚、设置临时钢横撑、缩短仰拱封闭距离等是保证大断面浅埋砂层隧道安全施工的有效方法，对其他类似工程施工提供了宝贵的工程经验。

Study of construction technology and mechanical effect of Guanjiao tunnel in shallow-buried sandy stratum in Xining-Golmud 2nd line

It is difficult to tunnelling in soft sandy stratum. To explore the key construction technology and study the mechanical effect of tunnelling in sandy stratum, numerical simulation and field experiments were carried out in sandy stratum section of Guanjiao tunnel. There existed about 450m long shallow-buried sandy stratum in the entry section of Guanjiao tunnel in the 2nd line between Xining and Golmud. Collapse had occurred during tunnelling using the initial three bench method; so four bench method was put forward. The excavation and support process of four bench method were simulated by means of FLAC3D numerical model, the deformation of surrounding rocks, ground settlement and stress distribution of primary support were analysed. And the superiority of the new method was proved by comparing the construction effect of three bench method. It was confirmed by actual construction and deformation measure that big arch-foot section, four bench excavation, long horizontal lead pipe-shed support, temporary transverse steel-support and shortening the distance of inverted arch closure were the key technologies of tunnelling in sandy stratum of Guanjiao tunnel. These methods could assure the safety of shallow-buried sandy stratum tunnel with big section. These could offer valuable experience to similar engineerings.