A Slate Tunnel Stability Analysis considering the Influence of Anisotropic Bedding Properties

Abstract

Bedding planes are the fundamental causes of anisotropic deformation and mechanical behaviors in slate, which will have great influence on tunnel stability. In order to analyse tunnel stability surrounded by slate, well-foliated slate in eastern Guizhou was taken as the specimen in tests. Microscopic analysis and test results show that slate can be regarded as a special continuous material. During the test, shear strength parameters and progressive failure varied when the direction of the bedding plane was changed, and two sets of reasonable shear strength were achieved by fitting. Numerical model verification is conducted before applying, and results indicate that the model can represent the anisotropic failure properties. So the model considering anisotropic shear strength simultaneously is utilized to analyse the tunnel stability in slate. When it is medium dip angle, the tunnel is significantly unstable especially for face and side walls, and at 45° (dip angle), the plastic zone depth ahead of the tunnel face can be the largest, being 1.7 times the tunnel height. The maximum deviator stress (σ1-σ3) is centralized on the middle of the side wall, and also, the stress (σ1-σ3) is the highest at 45° (dip angle), which will lead to shear failure.