The effect of ground drainage on the mechanical response of deep lined tunnels excavated in elastic and elasto-plastic materials

This paper revisits the classical problem of excavating a deep cylindrical tunnel in a saturated elastic porous ground that obeys Terzaghi's effective stress principle. A generalized form of the classical two-dimensional analytical solution by Lamé for the problem of excavating a circular tunnel in elastic medium subject to axi-symmetric loading is presented. The new solution considers the long-term (i.e., post-transient) mechanical effect of changes in pore pressure due to drainage of the ground around the opening on the mechanical response of the tunnel. This solution together with the analytical solution for axi-symmetric loading of an annular ring representing a liner are used to explain the effect that changes in pore-pressure in the ground have on the loads induced on the support. Analytical results are compared with results obtained with a finite difference code. The finite difference approach is also used to extend the analysis to cases in which the ground behaves inelastically.