中导洞——两台阶留核心土法在软弱围岩连拱隧道中的应用

Application on the middle drift-two bench with reserved core soil advancing construction method in multi-arch tunnel with weak surrounding rock

西南某隧道为双向四车道连拱隧道,隧道全长280m,按高速公路标准建设,设计速度80km/h。隧道围岩以强~中风化泥岩为主,富含蒙脱石等亲水矿物质,岩性软,岩体破碎,施工风险高。为确保施工安全,减小施工难度,降低施工成本,本文通过对隧道施工方案的比选,最终确定采用中导洞-两台阶留核心土法开挖。现场实施效果表明:本隧道Ⅴ级围岩浅埋及软弱段采用中导洞-两台阶留核心土法开挖是安全可行的,中导洞-两台阶留核心土法适用于双向四车道连拱隧道中围岩级别不差于Ⅴ级的软弱及浅埋偏压段。

One tunnel in the southwest is a multi-arch tunnel with two-directional and four lane highway, a total length of 280 m, and the design speed of 80km/h. The main surrounding rock is mudstone, which is rich in montmorillonite and other hydrophilic minerals. The lithology is soft and the rock mass is so fragmented, the construction risk is high. In order to ensure the safety of construction, reduce the difficulty of construction, and save the cost, through the comparative analysis of construction scheme, ultimately it determines to adopt middle drifttwo bench with reserved core soil advancing construction method. Field application result indicates that excavation with middle drift-two bench with reserved core soil advancing construction method for shallow and weak surrounding rock with grade 5 in this multi-arch tunnel is safe and feasible, and the method is suitable for shallow and weak surrounding rock which is not inferior to grade 5 in the multi-arch tunnel with two-directional and four lane highway.