Analysis of Surrounding Rock Displacement Induced by Tunnel Excavation in Horizontal Interbedding Rock Mass

Abstract

Material properties of horizontal sandstone and mudstone interbedding rock mass have significant differences in the horizontal and vertical directions. It is difficult to reveal the characteristic of surrounding rock displacement induced by tunnel excavation in horizontal interbedding rock mass by numerical methods based on isotropic constitutive models. Regarded as transversely isotropic medium, material parameters such as density, elastic modulus, poisson ratio etc. of interbedding rock mass are deduced. As an example, transversely isotropic constitutive model is taken into consideration in three dimensional numerical model of Luan Jiayan tunnel on Guangnan highway. The process of tunnel excavation is simulated in this model, and ground displacement distribution and variation with excavation steps are obtained. For the purpose of comparison, field tests of vault settlement and side wall convergence caused by tunnel construction are carried out. It is shown that compared with isotropic constitutive model, transversely isotropic constitutive model can reflect the physical difference in horizontal and vertical directions for interbedding rock mass of sandstone and mudstone. But transversely isotropic model is elastic, and plastic zone caused by tunnel excavation can’t be obtained. So there exist some differences from actual situation when this model is applied. INTRODUCTION In general, we regard sedimentary rock whose stratum bedding-plane is approximately level as horizontal stratum, and the altitude of the same rock formation for horizontal stratum is basically the same. In the process of Guangyuan-Nanchong expressway construction, tunnels are built to pass through mountainous region in the Sichuan Basin. Stratigraphic dip angle in tunnel site area is low and nearly horizontal;