Taking the large-section loess tunnel in Lanzhou-Chongqing railway as the project background

the initial support adaptability is comprehensively researched based on in-situ monitoring and 3D numerical analysis. The mechanical and deformational properties of the initial support are comprehensively analyzed; and then the results of numerical simulation are compared with in-situ monitoring data in order to get the state of stress and displacement which brought to the optimal parameters of the initial support after excavation. The initial support safety can be evaluated; meanwhile the concrete hardening behavior influences on the stress and deformation of the initial support have been analyzed by the FISH language of the fast Lagrangian analysis of continua in 3 dimensions(FLAC3D). The conclusions provide a reference for the design and construction of the tunnel engineering in loess area; and some useful experiences have also been accumulated