Design of complex tunnel portals
Advanced numerical analyses of tunnel portals are needed in case of several complex design conditions. Lombardi Ltd. provides studies in this field, using both commercial 2D and 3D numerical software as well as in-house developed softwares. Lombardi has gained specific experience by dealing with design cases of considerable complexity.
A study of particular relevance was the analysis of the portal of three tunnels located within a large slope of cohesionless soil. In this case, the close to limit equilibrium condition of the slope itself, as well as the diagonal entrance direction of the tunnels, called for 3D numerical modelling. The effects of the excavations on the slope stability were evaluated and the tunnel lining was designed, taking into account the staggered excavation start of the tunnels. Additionally, due to the high seismicity of the site area, seismic analyses were performed.
For the design of portal supports, a particular case to be studied was the entrance of a double tube road tunnel through a railway embankment. Because of the diagonal entrance direction of the tunnels, the use of permanent soil anchors in the design of the retaining structure would have interfered with the nearby tube, and was therefore not allowed. Therefore, the final design provided a support structure to withstand the long term earth pressure. The complex portal geometry required 3D numerical modelling. Furthermore, considering the tunnels passing underneath an existing railway line, possible settlements at the railtrack level had to be verified.
Start of services date
Civil designs; Special studies