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.
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