Abstract:

Based on analyzing the genesis, essential characteristics and tendencies of ground fissures in Xi’an, the physical model tests with a geometric proportion of 1:5 for active ground fissure and numerical simulation for the effect of active ground fissure on metro tunnel are carried out to study the design parameters of Xi’an metro line 2 tunnel orthogonally passing through the active ground fissure zones. On the basis of the average annual active rate of ground fissures and compared with the historical maximum displacements of ground fissures, the predicted and suggested maximum vertical displacements design values of each active ground fissure along the metro line 2 in the design life of 100 years are put forward. The test and simulation results show that the design width of metro tunnel orthogonally passing through the active ground fissure zone could be 60 m; i.e. 35 m in the hanging wall and 25 m in the footwall of active ground fissure zone. The stratum deformation along the tunnel axis ground fissure appears stepped mutational deformation; and integral descent of the hanging wall of ground fissure could be adopted in the design of tunnel longitudinal structure. Metro tunnel passing through the active ground fissure zones should be segmented by deformation joints to adapt the deformation of active ground fissures; the design length of sectional tunnel in main influence zone is 10 m; and in the minor influence zone that is 10 to 15 m. The conclusions will provide for reference to the design of lining structure of metro tunnel passing through the active ground fissure zones.

Key words: tunneling engineering, Xi’an metro line 2, ground fissure, maximum vertical displacement, treatment length of influence zone