既有公路下软基浅埋隧道综合修建技术的研究

研究目的：岑梧高速公路牛岭界隧道岑溪端洞口段存在多种复杂的不利因素（小型滑坡、浅埋、下卧软基、繁忙国道从上方通过），通过总结此段设计与施工方案，为今后类似工程提供参考和借鉴。 研究方法：采用工程类比和结构分析的方法进行研究和分析。 研究结果：通过分析和类比，确定采用超前双侧壁小导坑及钢管灌注桩来改善隧道基底承载能力的方案。 研究结论：双下侧导坑施工方案适用于浅埋特大跨、地表下沉量要求严格、围岩条件极差的隧道，且更着重于基础的处理。双下侧导坑断面小，易于操作和控制变形，采用全断面封闭支护，大大改善了导坑的受力状况。同时导坑的超前施工先行，可超前探明地质情况，提前处理基础，为整个隧道支护提供足够地基承载力；基础钢管桩能够提高桩问土的承载力，改善隧道仰拱基础，形成大仰拱基础，且能抵御隧道整体下沉。

Research on Comprehensive Construction Technique for Shallow Tunnel with Soft Foundation Under Existing Highway

Research purposes:There are many kinds of unfavourable factors in the opening section on Cenxi side of Niulingjie Tunnel of Cenwu Express Highway,such as small landslide,shallow,subjacent soft foundation and busy state highway passing through above.The purposes are to provide the reference to the similar construction in future through summing up the design and construction of this highway.Research methods:The research and analysis are made for construction of the tunnel by adopting engineering analogy and structural analysis methods.Research results:Through making analogy and analysis,it is decided to adopt the program of application of pilot tunnel with double-sided wall and steel pipe cast-in-place pile in construction so as to improve the bearing capacity of foundation base of the tunnel.Research conclusions:The construction program of adopting double-under-wall pilot tunnel is suitable for treatment of the foundation of shallow and extra large span tunnel which requires strict control of decline volume of surface under bad condition of building wall rock.It is easy to operate and control deformation because of the small section of double-under-wall pilot tunnel,and the stressed condition is improved much because of adopting the support with full section enclosure.In addition,the geological condition can be surveyed clearly and the foundation can be treated in advance for providing enough bearing capacity of foundation for supporting tunnel because of the construction of pilot tunnel in advance.The steel pipe pile for treating foundation can enhance the bearing capacity of the soils between the piles,improve the inverted arch foundation of the tunnel and form large inverted arch foundation against the settlement of entire tunnel.