Egnatia Odos - Tunnel T8
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The T8 tunnel is part of the new east-west Egnatia Odos motorway currently under construction in the north of Greece. The tunnel is located approx. 35km to the east of Ioannina. Construction commenced in September 2002. Two parallel tunnels, with a tunnel axis to tunnel axis distance of 26m, are being driven using the blasting drive technique and air-placed concrete method of construction. The two tunnel pipes are connected by means of crossways at distances of approx. 500m, which serve as emergency escape routes into the other pipe in the event of an accident occurring inside one or other of them. Furthermore, a 58m-long emergency lay-by is also to be constructed for each tunnel pipe.
Results of the ground investigation
The subsoil within the project area is made up of an alternating sequence of conglomerates, sandstone, silt and clay stone, which belong to the ionic flysch geological layer. The project area is permeated by a large number of sheer faults, most of which run in an approximately north-south direction. A further fault system, likewise with sheer faults, runs approximately in an east-west direction, such that the project area is divided up into a tectonic fault-block mosaic. Furthermore, the distance of the project area to the nappe zone of the Pindus Mountains on the West-Hellenic flysch syncline is only slight, such that the tectonics within the project area are also influenced by this process.
Tunnel driving and temporary support
The T8 tunnel is being driven using the blasting drive technique with preliminary crown driving and subsequent bench excavation. The temporary support takes the form of steel fibre air-placed concrete in multiple layers, walling arches and fully mortared rock anchors. Locally, drill pipe screens, particularly in the portal area, are used when driving through fault zones and in areas with less superposition. For particularly difficult subsoil conditions, such as when driving through larger fault and dispersion zones, a temporary crown floor and/or a permanently sealed tunnel floor is provided.
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