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The paper presents a mountain road tunnel in Portugal, part of IP2 highway, in Castelo Branco district, with a length of 1570m and a maximum overburden of 237m. The tunnel was open to the traffic at the end of 1997. In the paper the more important geologic and geotechnical aspects of the work, and the details related to the project, namely excavation methods, primary and final supports are presented. During the opening of the tunnel, some pathologies have occurred, which seemed to indicate a certain instability of the slope on the north portal. A specific monitoring system was set up. The paper refers some of the results that are considered to be the most representative of the tests performed and which were obtained during observation. An analysis of the structural behaviour has been performed based on numerical models. Some few Considerations are made as regards the experience acquired during construction. 1. INTRODUCTION The paper contains an analysis into the structural behaviour of a mountain tunnel, part of the 2 highway between Alpedrinha and Fundão, in Castelo Branco district, Portugal. It corresponds to a section of a road with 1780m length, the tunnel section being 1450m long (Leme and Inacio, 1997). It is a road tunnel with horseshoe section, a maximum height of 6.8m, a maximum width of about 11.7m and a maximum overburden of 237m (Figs. 1 e 2). The construction works began in 1994 and were completed by the end of 1997. The work refers to the main geological aspects of formations involved by the work. special reference being made to the geomechanical studies.and tests conducted, as well as to the results obtained by application of empirical systems, particularly the systems Q, RMR and MR. The construction methods adopted are presented, especially as refers to the excavation sequences and to the supports used for the different geomechanical zones. During the opening of the tunnel, some pathologies have occurred, which seemed to indicate a certain instability of the slope of the north portal, which has led to set up a specific monitoring system, other than the general monitoring system of the tunnel. Furthermore, an analysis of the structural behaviour has been performed based on finite element numerical models. Considerations are made as regards the experience acquired during construction. 2. GEOMECHANICAL CHARACTERISTICS OF THE ROCK MASS The tunnel layout involves a rock mass that is morphologically conditioned by two lithological units, one of essentially granitic nature and the other of a schist-greywacke and metamorphised nature (Fig. 2). The two jointed formations have three main families presenting almost similar directions along the tunnel layout, two being sub-vertical N40- 70W and N-S and a third one being almost perpendicular to the intersection of the two plans mentioned, with an inclination to south ranging from 15 to 300 (Coba, 1996; Leme and lnacio, 1997). 12 boreholes were executed, which has made it possible to carry out the macroscopic lithologic classification, the assessment of discontinuities and weathering, as well as to obtain the RQD value.