Numerical Analysis For Construction Of Large Cross-Section Loess Tunnel In High-Speed Railway

Based on the comprehensive analysis of current development level of large cross-section loess tunnel, the thesis is combined tightly with loess tunnel in Zhengzhou-Xi'an passenger-dedicated lines. In order to solve key construction technique of large cross-section loess tunnel in high-speed railway, finite difference method and finite element program ANSYS are applied to research the effect of foundation treatment, different construction methods and the safety performance of secondary lining. Finally, some useful conclusion and suggestion are given.Aimed at collapsibility loess foundation, cement-soil compaction pile, one kind of composite foundation treatment methods, is provided, and three-dimensional numerical modeling is used to calculate foundation settlement occurring in opening oblique cutting segment, cut-and-coverzone, underground excavation segment and transition partitions between bridge and tunnel. Finally, the foundation treatment measurement is proved to be suitable, and some advice is given.Three-dimensional mechanical performance of primary support under different construction conditions is analyzed by using numerical modeling method. Through four different excavation methods, which are named as curve drift heading, CD, CRD and two-side wall drift heading method, respectively, safety performance of primary support and its effect of confining the wall rock deformation is researched, and the quality of these methods are assessed to recommend proper excavation method for corresponding conditions.Secondary lining structure is computed and analyzed for conditions of shallow burial, deep burial, earthquake region, unsymmetrical pressure and cut-and-cover tunnel, individually, and then safety evaluation of secondary lining is obtained.Research results had been utilized to guide design practice, and good effect is achieved.