关键词: 山岭隧道, 横观各向同性, 有限元法, 近水平岩层, 现场测试

Abstract: Approximate horizontal soft-hard inter-bedding rock is equivalent to the transverse isotropy rock，and its material parameters are deduced，such as density，elastic modulus，poisson ratio，etc． With the Wenjiaya tunnel in the Guang-Nan expressway as the analysis object，according to the parameters of transverse isotropic surrounding rock，the plane strain finite element model is established． And combining with the field test data，the primary support’s stress state in the process of the step cut method of the approximate horizontal layer weak rock is analyzed． Research shows that after the excavation of the upper step，the primary support is forced by the axial pressure，and vault and arch wall waist bend inward，while arch back bends outward; after the excavation of the lower step，the primary support continues to be governed by the axial pressure，and vaults and inverted arch invert inwards，while arch back and wall waist bend outward． Research conclusions correspond with the phenomenon of vault settlement and arched bottom uplifting．

Key words: mountain tunnel, transverse isotropy, finite element method, approximate horizontal rock, field testing