A numerical model of the excavation works for underground railways using finite element meshes is presented in this paper. To simulate the actual tunnelling procedure several steps of the construction works have been considered in the analysis. Several meshes containing finite element and infinite domain elements have been used in this research and interaction between soil and tunnel structure has been taken into account by including gap elements. The methodology used has allowed to identify settlement induced by the excavation and numerical results are in agreement with the actual values obtained in the new lines of the Madrid underground railways system excavated during the years 1996–1999.
Tunnelling works required by the extension of the underground railways system in Madrid were carried out with a full face tunnelling boring machine (TBM) having an earth pressure balance system to stabilize the excavation front. The whole system consists of a steel shield containing the extraction machinery, and the hydraulic jacks. The shield is centered with respect to excavated hole by steel plates located on the lower part of the shield. After tunnelling a tunnel structure is created by pre-cast concrete segments. A grouting mortar is also pumped into the gap between the soil and concrete element surfaces.
While the excavation procedure in underground works and the settlement induced are by nature threedimensional (Attewell et al., 1986), mainly in the vicinity of tunnel front, they produce displacement fields close to a plain strain state at the rear part of the tunnel. Also, if the construction system includes an earth pressure balance system the 3-D effects are very much attenuated, and it is possible to reproduce the tunnelling procedure by recreating the most important steps of the process with 2-D finite element models.
