浅埋超大跨四线高铁隧道施工方法及开挖响应——以杭台高铁下北山1号隧道为例

Construction Method and Excavation Response of Shallow-Buried Super-Large-Span Four-Track High-Speed Railway Tunnel:a Case Study of Xiabeishan No.1 Tunnel on Hangzhou-Taizhou High-Speed Railway

为掌握浅埋超大跨隧道的开挖力学响应行为,以开挖跨度为26.3 m、覆土为6~35 m的四线高铁隧道为工程背景,基于数值模拟对不同施工方法的开挖力学响应进行研究,结果表明复合双侧壁导坑法和双侧壁导坑法的围岩稳定性和支护结构安全性均优于提出的其他工法。现场监测结果表明:1)双侧壁导坑法开挖时超大跨隧道围岩变形主要发生在导洞上台阶开挖初期,临时支撑拆除对围岩变形的影响较小;下台阶初期支护的受力较小,上台阶初期支护是主要的承载结构。2)初期支护的安全系数富余较大,基于经验类比得到的支护参数偏于保守,可对喷射混凝土厚度作减薄优化。3)中导洞中下台阶的开挖会导致临时支撑的作用下降,提出双侧壁导坑法取消下部临时支撑及优化开挖分部的措施,探讨采用台阶法的可行性。

To investigate the mechanical response behavior of excavation of shallow-buried super-large-span tunnel,a case study is conducted on a four-track high-speed railway tunnel with a excavation span of 26.3 m and soil covering of 6~35 m using numerical simulation method under various construction methods.The results show that the stability of surrounding rock and the safety of supporting structure using composite double-side drift method(CDDM)and doubleside drift method(DSDM)are better than those using other construction methods.The field monitoring results reveal the following:(1)During DSDM excavation,the surrounding rock deformation of super-large-span tunnel mainly occurs at the initial stage of top heading excavation of guide tunnel,and the removal of temporary support has little influence on surrounding rock deformation;the force of the primary support of the lower bench is small,while the primary support of the top heading is the main bearing structure.(2)The safety factor surplus of the primary support is large,and the supporting parameters obtained based on empirical analogy are conservative,so the thickness of shotcrete can be reduced and optimized.(3)The excavation of the lower bench in the middle guide tunnel will lead to the decline of the temporary support function,and the measures using DSDM to cancel the lower temporary support and optimize the excavation section are put forward,and the feasibility of the bench method is discussed.