Squeezing effects in the excavation of deep tunnels

Difficult conditions in mechanized tunnelling can be met when the rock mass behaviour is time dependent and the so called squeezing condition develops. In this case, large radial pressures on the tunnel boring machine and on the supports are expected in the short and long term. The results of some finite element analyses, in plane strain and axisymmetric regimes, are here discussed concerning the full face excavation of a deep circular tunnel. An elasto-visco-plastic constitutive model that accounts for tertiary creep has been adopted and calibrated on the basis of laboratory test data. Some comments are drawn on the effects of tertiary creep and on the influence of the tunnel face advance on the closure of the opening and on the stress redistribution around it.