FINITE ELEMENT SIMULATION OF THE EXCAVATION-INDUCED DEFORMATION IN TUNNELS DRIVEN IN POROELASTIC MEDIA

Resumo

The present paper deals with the formulation of a constitutive and computational model for
the analysis of the deformations induced by the excavation of a tunnel in a saturated poroelastic medium.
The finite element implementation relies upon the discretization of weak forms of local momentum and
fluid mass balance equations in the context of infinitesimal skeleton strains. The simulations of the steps
of excavation as well as placement of the concrete lining are modeled by the method of
activating/deactivating elements. The accuracy of the finite element approach is assessed by comparison
with available analytical and semi-analytical solutions developed for a circular tunnel driven in a
poroelastic medium. The numerical simulations notably show that the strain and stress fields developed
around the tunnel will depend on the depth, cross-section geometry, surface load distribution, soil
poroelastic properties, permeability coefficient and soil porosity. They also allow for the calculation of
seepage forces due to pressure gradient induced by excavation and acting on the tunnel wall and tunnel
face.