ABSTRACT
The Maly Lubon Tunnel is the longest tunnel in Poland, as part of the expressway S7 Krakow–Rabka Zdroj investment. It is twin tube tunnel 2 km long with sections 220 m2 large, excavated through Maly Lubon mountain by Astaldi company. The tunnel, still under construction, excavated in the Carpathians, consists of alternative layers of sandstone and shale with high variable degree of weathering. Due to the extreme variability of the rock mass behaviour, it was decided to change the excavation technology from the NATM to the Convergence-Confinement method. The big challenge of this change required a new design for the South portal, in the most weathered and heavily tectonized Flysch, already subject to large displacements during its geological history. Soil-structure interaction analysis were also carried out for a wider tunnel section which included emergency lanes and a vehicular cross passage intersecting with an additional technological tunnel. In order to study the complex geometry of the intersections between tunnels and the mutual effects potentially induced by the excavation of each tunnel, a specific 3D FEM analysis was carried out and provided a valid support to select suitable construction phases during the construction. The aim of the present paper is to describe the problems encountered during the excavation of a large road tunnel in Carpathian Flysch and to outlines the design solutions adopted to overcome the most critical sections of excavation.
