(1. Department of Civil Engineering，Logistical Engineering University，Chongqing 401311，China；2. Chongqing Engineering and Technology Research Center of Geological Hazard Prevention and Treatment，Chongqing 400041，China； 3. Institute of Rock and Soil Mechanics，Chinese Academy of Sciences，Wuhan，Hubei 430071，China)
Abstract：In order to obtain the regularity of mechanics for an unlined tunnel during earthquake，strength reduction finite element method and a large finite-difference program FLAC with tensile and shear failure analyses are combined and introduced into the tunnel stability analysis. Based on static analysis of loess unlined tunnels，a seismic dynamic finite element static analysis and a complete dynamic stability analysis methods are proposed. The analysis takes into account the tunnel tensile and shear failure to get the failure mechanism of loess tunnel with outside drive. Partial tensile failure is taken place at the top and then the general demolition is took place at the broadside of the tunnel. And it is found that the strength reduction finite element method can be used not only to tunnel static analysis but also to tunnel dynamic stability analysis. This analysis can provide a theoretical basis for seismic design of unlined cavern loess habitat，and it can be used as a foundation for seismic response analysis of loess tunnel with lining.
