Effect of relative orientation of anisotropy planes to tunnel axis on the magnitude of tunnelling displacements

Abstract

When analysing the measured displacements at the Trojane tunnel (Slovenia), excavated in soft foliated rock mass, some interesting deformation patterns were observed, especially large surface settlements that appeared despite quick ring closure, stiff lining and consequently small tunnel lining displacement. It soon became clear that most of these phenomena are the consequences of highly anisotropic nature of the soft foliated rock mass. A vast number of numerical analyses were performed, varying dip direction and dip angle of the anisotropy planes as well as strength and stiffness parameters of the rock mass (degree of rock mass anisotropy). The share of displacements that occur ahead of the tunnel face and the extent of influential zone ahead of the tunnel face are presented as primary results. Further on, the effect of tunnelling with and against the anisotropy planes in the same material is presented. The effect of overburden above the tunnel and the influence of the orientation of anisotropy plane on the surface settlements were investigated. To verify the obtained numerical results, comparisons to the measurements inside and above the Trojane tunnel were made.