The Rossio railway tunnel was built in 1890, about 2600m long, crossing several formations involving limestones, basalts and also sandy and clayey formations. Recently a new tunnel from the Lisbon Metro was executed above and normal to the railway tunnel with a short distance between the lower part of the metro tunnel and the railway one. A reinforcement support system was designed in the Rossio tunnel in order to assure its stability. The reinforced system comprised the use of grouted bolts and shotcrete. A monitoring system was implemented in order to observe the structural effects induced by the construction of the Metro tunnel in the Rossio tunnel. In this communication the construction procedure is analysed as well as the geomechanical tests performed that involved in situ and laboratory tests and the monitoring tests. For the interpretation of the obtained information a complex 3D model was built using the software FLAC3D, permitting the simulation of the sequential excavation scheme used and non-linear behaviour of the rock and soil formations, and the different support systems used. A simplified seismic was also performed in order to evaluate the influence of an earthquake in both underground structures. Some significant results and final considerations are presented.
The Rossio tunnel was built in 1890, with a masonry vault composed of bricks, with a thickness of 80cm, and the walls in stone or brick masonry. The tunnel has a length of about 2600m. It is located in Lisbon, inside a hill between the valleys of Avenida da Liberdade and Sao Bento. In the initial stretch, from the Rossio station until km 0.780, it crosses, at a shallow depth, clayey-sandy formations, some of them with significant permeability. In the intermediate stretch, limestones and marls are found, with important flow of water through the discontinuities of the rock mass. In the final stretch, the geological formations comprise basalts, marls and highly fractured limestones (Choffat, 1889; Sousa, 1998). The internal tunnel cross-section was designed with a maximum width of 8m, formed by a circular vault of 4m radius, and maximum height of about 6.5m (Figure 1). The tunnel was constructed according the well-known Belgian method, that considered the following phases (Cabral, 1987): i) excavation of a pilot gallery in the centre of the upper part of the section; ii) lateral enlargements of the upper part; iii) construction of the brick masonry vault, and subsequent filling of the void between the ground and the vault with stones; iv) excavation of the lower central section and subsequent lateral enlargements; and v) execution of the walls in stone or bricks in case of lower. The use of this construction methodology was one of the main reasons for the settlements and ground movements, as well as the occurrence of voids between the masonry and the ground. Recently, the Rotunda-Rate line of the Lisbon Metro was constructed, starting at the Rotunda II station, followed by the Braancamp and the Herculano runnels and ending at the Rato underground station.
