FEM 3D Analysis of Settlements Induced by Shallow Tunnels in Coarse-Grained Soils

The paper is focused on some aspects of 3D numerical modelling of shield-driven tunnels in coarse-grained soils. Different approaches for modelling soil-shield interaction are considered and their impact on the predicted settlement trough is analyzed. These approaches have been applied for modelling two well documented case histories of one tunnel bored in green field conditions. The tunneling process has been simulated step-by-step in order to represent relevant features, such as, application of face pressure, installation of a segmental lining, grout injection and time-dependent variation of grout stiffness. The soil mechanical behavior has been modelled by the Hardening soil model with small strain stiffness implemented in the Plaxis 3D software. Soil deformation around the shield has been modelled by three different approaches: Shield contraction, E-modulus reduction and Strain applied method. Settlement distributions obtained by E-modulus reduction and imposed strain methods are generally in better agreement with field monitoring data but require a specific calibration. Numerical results concerning the structural forces in the lining and the stress paths of representative soil elements are also discussed

Numerical analysis of tunnelling in sand - a case study of a centrifuge test

Ground movement induced by TBM tunnelling in sand has been the subject of much discussion in recent years. It is commonly agreed that prediction of the ground movement trough in cohesionless soil is not easy. The main cause of ground movement in TBM projects is the tunnel volume loss induced by shield over-cutting and the dimensional difference between the shield and the lining. Numerical modelling could be a useful tool for ground movement prediction especially when dealing with projects where complex underground structures and strata distributions are involved. This paper employs the commercial FEM software Plaxis 3D in simulating of a centrifuge TBM tunnelling prototype using the constitutive model suggested by the software in analyzing behaviour of sands. Some popular empirical and analytical approaches of predicting ground movements are also adapted for the purpose of comparing with the numerical results