大断面山岭隧道预留核心土环形开挖法与上下台阶法的比较分析——以浙江奇坑隧道出口段施工方案比选为例

A Comparison between Two Tunneling Methods (SEM and THBM) for Large Cross-Section Mountain Tunnel—A Case Study of Qikeng Tunnel in Zhejiang Driven

预留核心土环形开挖法和上下台阶法是软弱破碎围岩大跨度山岭隧道掘进的重要方法。本文采用三维有限元数值模拟方法对浙江奇坑隧道的预留核心土环形开挖法和上下台阶法方案进行了计算分析,提出了以掌子面挤出变形作为量化指标的评价方法,采用折减系数法比较了两种施工方案下的掌子面稳定性情况。本文还对现场实测结果和数值计算结果进行了比较分析。研究表明,预留核心土的几何形状和台阶步长对掌子面挤出变形密切相关,在控制掌子面挤出变形和维持掌子面围岩稳定上,上下台阶法结合管棚超前加固可达到预留核心土环形开挖法同样效果,且可为大型机械施工创造较好条件,提高了施工效率。本文的研究方法和结论可为类似工程提供借鉴。

Sequential excavation method (SEM) and top heading and bench method (THBM) are two important excavation methods for large cross-section mountain tunnels buried in weak ground. Based on 3D-FEM numerical analysis of Qikeng Tunnel, which is located in Hangzhou city of Zhejiang Province, this paper presents a comparison of tunnel’s behavior between when tunneling by SEM and by THBM, using workface extrusion and crown settlement as appraisal indices and adopting reduction strength coefficient method for the calculation of the slope stability of tunnel front face. In the end, this paper carries out a comparison between the site measurements and calculation results. The study of this paper shows that the core extrusion of workface, in SEM, depends heavily on the shape and length of core rock, and that THBM, when combined together with forepoling, can achieve the same goal as that of SEM in confining the workface extrusion and keeping front face stable. The research approach and its conclusion can be used as reference for other similar projects.