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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。
A tunnel in the southwest is a two-way four-lane multi-arch tunnel with a total length of 280m. It is constructed according to the expressway standard with a design speed of 80km / h. The surrounding rock of the tunnel is dominated by strong to moderately weathered mudstone and rich in hydrophilic minerals such as montmorillonite. The lithology is soft and the rock mass is crushed, resulting in high construction risk. In order to ensure the construction safety, reduce the construction difficulty and reduce the construction cost, this paper finally chooses the pilot tunnel through the comparison and selection of the tunnel construction plan - excavation of the two steps left core soil method. The on-site implementation results show that the shallow grade Ⅴ surrounding rock of the tunnel and the middle guide tunnel in the weak section are feasible. Excavation of the core with two steps is safe and feasible. The middle guide tunnel - Surrounding rock arch in the tunnel level is not worse than Ⅴ level weak and shallow bias section.