Numerical modelling of a NATM tunnel construction in London Clay

The finite element program CRItical State Program (CRISP) has been used to model the New Austrian Tunnelling Method (NATM) in London Clay. The non-linear behaviour of the London Clay was modelled by a Strain Dependent Modified Cam Clay (SDMCC) model and the tunnel lining was modelled by constant and time-dependent elastic models. The construction process was modelled in two and three dimensions by removing soil elements in sequence. The tunnel lining was either assumed wished-in-place or introduced after the excavation of each panel. The results obtained from plane strain and three dimensional analyses are compared to assess the importance of arching of soil ahead of tunnel face.