Numerical Analysis of a Tunnel in an Anisotropy Rock Mass. Envalira Tunnel (Principality of Andorra)

Abstract

The Envalira Tunnel (Principality of Andorra) passes through a rock mass of phyllite and quarzite, and its construction had some parts with great difficulties due to the different mylonite zones and fractured strips that generate a weak plane orientation. In those zones, great deformations were measured concentrated in one side of the section, showing a strong asymmetric behaviour. There were some sections of the tunnel that had many instrumental implementations to control its behaviour. With all these data, it has been possible to build a numeric model of finite element method that reproduces the tensional and deformational behaviour of the tunnel in order to compare the results obtained with the measured data. The interest of this case was how to model the anisotropy of the rock mass and to get as a result the asymmetry behaviour in tensions and deformations. For that purpose , it was thought to work with a "jointed rock model" that is available in the commercial program Plaxis. The results of the numerical model seems to have a good setting with the real behaviour of the tunnel, reproducing quite well the asymmetric problems on deformation and tension distribution onto the support.