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ABSTRACT Metro do Porto is a major light rail infrastructure built in the city of Porto and surrounding municipalities. In Porto's downtown, classified by UNESCO as World Heritage, the metro was built underground. From a technical point of view, one of the most challenging underground metro stations due to the geomechanical unique heterogeneous characteristics of the granite rock mass is the HeroÍsmo station. This station was the first to be built. To better understand the behaviour and interaction of the structures with the surrounding rock masses numerical models were carried out. The geomechanical properties of the granite formations were given by the designer and also obtained through the software GEOPAT. The models' outputs were compared with the monitored results in order to validate the structural behaviour of the underground station.
1 PORTO METRO UNDERGROUNDWORKS Metro do Porto is one of the largest metro network built at once in Europe.As the historic centre of Porto is classified asWorld Heritage by UNESCO, the metro lines in that zone were constructed underground. The HeroÍsmo station is located there, between the Campanhã and the Campo 24 de Agosto stations, which are inserted in the C line of Metro do Porto. The HeroÍsmo station may be considered one of the most important stations in the network (Babendererde et al., 2006; Cardoso et al, 2006), (Fig. 1).
2 HEROÍSMO STATION The station, being one of the most complex of the Porto Metro system, is composed by four tunnels, two main ones and the other two for ventilation purposes, and a shaft that provides accesses from the surface to the boarding area (Figs. 2 and 3). The station's structure is of the mixed type, with a body that was excavated on open-sky, which constitutes the attack shaft and where the accesses and the station's technical facilities were installed. The geometry of the shaft is practically rectangular, with about 52m long and a width varying between 16 and 25 m, occupying a total area of 1035m2, with a maximum excavation depth of 29 m. Tunnel 1 is situated in the South extension of the shaft and integrates the accesses to the station's South boarding platforms. The respective excavation cross section has about 232m2 of area, being the tunnel 30m long with an overburden of only 11m. Attached reinforced jet-grouting columns with 0.5m of diameter were constructed as pre-support (Cardoso et al, 2006). The excavation was conducted in three levels, totalling eight executing phases, with a 1.0m advance each and installation of the primary lining, composed by trusses of steel cranks associated with 0.40m of shotcrete. The secondary lining is composed by a 0.45m layer of reinforced concrete. Tunnels 2 and 3 have a 24m2 cross section area. Tunnel 2 is situated on the East side and is 58m long while tunnel 3, located on the West side, has a length of 47 m. Both tunnelswere executed with an overburden of 19m approximately.
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