Finite element modelling of a tunneling process in granular soil

The construction of tunnels in granular deposits often requires the preliminary grouting of the soil mass to stabilize the opening before its temporary support is installed. When applied to shallow tunnels in urban areas this procedure could induce heaves of the ground surface, which are followed by settlements during excavation, with consequent damages of existing buildings. The application of two elastic-plastic finite element approaches in discussed here for evaluating the displacements induced by this technology. The critical evaluation of the numerical results shows the limits of an approach that simulates the grouting process through a non-elastic volume strain. To overcome them an alternative scheme is adopted based on the application of a neutral pressure within the grouted zone. This method leads to a better estimation of the displacements measured in situ during the tunnel construction. The numerical results demonstrate also the relevant role of the plastic flow rule on the predicted surface displacements.