Does Elastic Anisotropy Significantly Affect a Tunnel's Plane Strain Behavior?

Abstract

Rock masses are anisotropic because their properties depend on the orientation considered. The diverging opinions in the literature on whether the elastic anisotropy of a rock mass significantly affects the plane strain behavior of a tunnel are contrasted. A two-dimensional parametric study is presented to answer the questions raised by the literature review. For a given premining state of stress, the stress field around a tunnel in an anisotropic rock mass is not significantly different from the stress field around a tunnel in an isotropic rock mass. For a given anisotropic rock mass, the stress and displacement fields, as well as slip zones, obtained under the hypothesis of no lateral strain are radically different from that obtained under the hypothesis of uniform premining state of stress. In the first case, the slip zones can penetrate more than two diameters into the rock mass, especially for vertical or inclined joints. In the second case, the slip zones extend for a maximum of half a tunnel diameter into the rock mass, regardless of rock mass anisotropy. Displacement vector magnitudes are highly influenced by the elastic anisotropy of the rock mass, even if the premining state of stress is fixed. For a given premining state of stress, slip zones around a tunnel are unaffected by the elastic anisotropy of the rock mass. The slip zones depend only on the orientation of the joints along which slippage can occur.