Abstract:

The partial excavation methods, i.e. CD method and CRD method, are usually adopted in portal section construction of shallowcovered new loess tunnel. But many problems, i.e. large amount of temporary support dismantling, unusable large construction machinery and low working efficiency, restrict the tunnel construction. The micro bench method, takes the micro bench excavation, rapid primary support by wet jet manipulator and rapid inverted arch ring closure as the cores, is proposed by taking loess tunnels on Menghua Railway for examples. And then the tunnel primary support deformation, plastic zone of surrounding rock and internal forces and safety coefficient of primary support structure of Zhangyu #2 Tunnel are analyzed by numerical simulation method, so as to verify the rationality of micro bench method. Finally, the deformation monitoring data, resource investment and construction schedule of loess tunnels on Menghua Railway are analyzed. The analytical results show that by adopting the micro bench method, the primary support deformation is small, the footage of 45-67.5 meter per month is achieved; largescale construction machinery is available; the construction efficiency is improved greatly; and the construction cost is reduced.

Key words: Menghua Railway, shallowcovered new loess tunnel, micro bench method, inverted arch ring closure, construction technology