The tunnel of Bois de Peu is part of a project of the south-eastern Besançon (France) by-pass. An exploration gallery permitted to highlight the presence of eighteen geological units and to distinguish four sorts of materials: limestone, marls, clays and interbedings of marls and limestone. Despite of the important number of laboratory and in situ tests carried out, many uncertainties remained on the mechanical parameters value and on the position of the different geological units. So, it was decided to apply the interactive design method during the construction to adapt the excavation and support to the actual conditions found. In the framework of this method, an important monitoring program was foreseen. This article shows the behavior observed in the different kind of soils. In the clayey zone where the support is the most complex, strains in the ground and in steel ribs are monitored. Finally, the available measurements permit to better understand the behavior of soil-structure interaction problems.