Laboratory model tests and numerical analysis of shallow tunnels

The stress analysis of shallow tunnels in weak rocks, or "hard" soils, may present some difficulties caused by its three dimensional nature and by the particular mechanical behaviour of these materials, which show a reduction of stiffness and shear strength with increasing shear deformation. This problem is here approached, with particular reference to the stability of the tunnel face, from both numerical and experimental view points. The experimental part of this study consists of a series of tests on a 3D, reduced scale, 1g model that led to a quantitative evaluation of the displacements induced by the excavation. The problem was then analyzed through 2D and 3D finite element analyses, accounting also for "softening" material behaviour. The comparison between experimental and numerical results permits to draw some conclusion on the effectiveness of the adopted numerical models in the analysis of tunnels.