A finite strain closed-form solution for the elastoplastic ground response curve in tunnelling

The ground response to tunnel excavation is usually described in terms of the characteristic line of the ground (also called 'ground response curve', GRC), which relates the support pressure to the displacement of the tunnel wall. Under heavily squeezing conditions, very large convergences may take place, sometimes exceeding 10-20% of the excavated tunnel radius, whereas most of the existing formulations for the GRC are based on the infinitesimal deformation theory. This paper presents an exact closed-form analytical solution for the ground response around cylindrical and spherical openings unloaded from isotropic and uniform stress states, incorporating finite deformations and linearly elastic-perfectly plastic rock behaviour obeying the Mohr-Coulomb failure criterion with a non-associated flow rule. Additionally, the influence of out-of-plane stress in the case of cylindrical cavities under plane-strain conditions is examined. The solution is presented in the form of dimensionless design charts covering the practically relevant parameter range. Finally, an application example is included with reference to a section of the Gotthard Base tunnel crossing heavily squeezing ground. The expressions derived can be used for preliminary convergence assessments and as valuable benchmarks for finite strain numerical analyses. Copyright (C) 2014 John Wiley & Sons, Ltd.