The paper presents the Canical tunnel, under construction on Madeira Island. It is referred to the geometric characteristics of the tunnel, to the formations involved and to the construction methods adopted for the different geomechanical works. It also contains a statistical processing of geotechnical data by introducing probabilistic approximations and defining the geomechanical parameters of the rock mass based on empirical methodologies. On the basis of that analysis, a study of the structural behaviour of the tunnel is performed using finite element nUmerical models.

1. INTRODUCTION

This Work presents a geotechnical study done for the two-gallery Canical tunnel, Madeira Island. The tunnel is part of the layout of the highway that connects Machico to Canical. It Involves different formations; each of the zones mentioned comprising material that even though belonging to the same formation presents different extremely variable characteristics. The construction of the tunnel is achieved in accordance with a sequential method, the excavation face following different configurations depending on the strength of the formation involved. The study comprises the modelling of a section for different materials that are within the geomechanical formations involved. In view of the complexity in characterising the formations, it has been considered as adequate and effective to carry out a statistic processing of the geotechnical data. The latter has been performed in accordance with the Monte Carlo method, introducing the theory of probabilities to define the parameters of the rock mass. Therefore, for each formation, the numerical modelling of a type section of the tunnel has been done, by considering different situations for the geomechanical parameters. For one of the geomechanical zones, the characteristics corresponding to the percentages of 5%, 50% and 95% have been considered which is intended to cover all the range of geotechnical materials. The results of the study done are namely related with the analysis of the field of stresses and deformations in the rock mass (and study of the influence of the opening of a section on the stresses and displacements of the rock mass in the vicinity of another section), as well as with the values of the safety factors and their space distribution in the rock mass and with loads on supports.

2. CHARACTERISTICS OF THE TUNNEL

The Canical tunnel is a double road tunnel, separated by a septum of about 15m, the longitudinal development is about 1 980m. The cross-section of the tunnels is variable. Fig. 1 shows a current superficial section, which has been the object of study in the analyses done. The cross-section of the tunnels has about 9.0m width and the internal contour consists of a semi-circular arch with 4.5m radius, which forms the arch and being vertically extended by walls. The minimum setting out line is of 5.0m, which makes it possible to ensure the necessary space for the installation of equipment at the central zone (since there the setting out line is significantly higher than 5.0m). Fig. 2 shows a plan in the proximity of a portal.

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