Material behaviour associated with tunnelling through the weak rock masses of the Alpine system in Northern Greece

Abstract

The backdrop for this research paper is the tunnelling that is currently nearing completion in the Epirus and Western Macedonia regions of Northern Greece, as part of the Egnatia Odos Highway construction. Highly deformed and altered sediments and low grade metamorphic rock masses dominate the near surface environment creating a variety of technical challenges for tunnelling. Accurate equivalent rock mass performance predictions for tunnels in these materials (including yield and residual strength as well as flow and dilation considerations) is complicated by geomorphologic peculiarities (mixed face conditions, variable orientation or rock masses and structure) such as flysch materials. In addition, portal stability problems, and geometrical issues such as the effects of simultaneous twin tunnel excavation on radial displacements of each bore are also key considerations. This work involves the use of 2D and 3D research models of tunnel sequencing for numerical simulation of composite material behaviour and sequential tunnel deformation response with a goal to investigating the strength and deformation of heterogeneous rockmasses. A discussion of the geological conditions, material property determination, monitoring data and the model calibration strategy is given. The focus is on the Driskos tunnel, the longest of the project.