Abstract:

During the construction of Zhangmao large crosssectional tunnel in loess on ZhengzhouXi’an highspeed railway, various technical problems were met. In this paper, the construction technologies for large crosssectional tunnel in loess are proposed on the basis of field tests and theoretical analysis. The results show that: 1) The axial force of the anchor bolt is smaller than 12 kN in the support system. The tunnel arch is under compression and the side wall is under tension. 2) The average stress on the shapedsteel is 132 MPa, and that on the girder is 86 MPa. The stress imposed on the girder is even. 3) The deformation allowance of the surrounding rock Grade V is 25~28 cm, and that for Grade IV is 10~15 cm. 4) The critical value between deep and shallow overburden is 40~60 m. 5) The measured contact stress between the primary support and surrounding rock is smaller than theoretical calculations. 6) The secondary lining of shallow tunnel shares 50% of load, and the secondary lining of deep tunnel shares 10% of load. 7) The vibration excitation test shows that the value of invert settlement is smaller than 0.5 mm after 2, 300, 000 times of excitation, and the saturated loess beneath the tunnel floor never goes soften or argillized. 8) The threestep excavation method is preferred for largediameter tunnel construction in loess. 9) The ground surface settlement can be controlled within 5 cm when double side drift method is used in construction of shallow sandy loess tunnel undercrossing highway. 10) The cementsoil compaction piles can be used to eliminate the collapsibility of loess. 11) The drainage scheme of “drainage taks the first place” is suitable for tunnel construction in saturated loess. 

Key words: ZhengzhouXi’an highspeed railway, tunnel construction in loess, supporting parameters, construction technology, settlement control, foundation treatment, water proof and drainage