ABSTRACT
The case study is concerning about the crossing of an Alpine geological Fault with the excavation of the pilot tunnel and followed by the two tunnel lines. During the excavation phases, the Contractor has founded for tunnel lines a significant amount of sprayed concrete, due to the filling of the overbreaks arisen behind the steel ribs support, despite the boundary consolidation. This issue has opened the dispute between Contractor and Owner and it has been resolved through the measurements in situ and by analysis of the related consolidation system planned in the Project. From the analysis, it was found out that the consolidation system, originally planned for the pilot tunnel and then adopted at the tunnels project line, did not give back the expected effect of the upgrading of rock mass. Therefore, the arisen overbreaks have obliged the Contractor to fill them supporting extra costs, refunded later by the Owner.
