Impregilo, in JV with Greek contractor Aktor, was recently awarded a contract to build an 11km long motorway extension in central Greece, including the construction of 6.4km of tunnels through some of the country’s mountainous coastal countryside.
Impregilo/Aktor JV was awarded the US$146M contract by the Greek motorway authority Eyde/Motorway Pathe, which has agreed to review the prices of construction during the course of the four-year project.
Two 8.5m diameter twin tube tunnels (the 700m long Dichalorematos tunnel, and the 2.5km long Knimidos tunnel) will be built. The Knimidos tunnel, which will run through highly fractured dolomites and limestone, will be excavated from both sides, primarily to meet the tight time schedule. The crown will be excavated first, followed by the bench at a distance of about ten tunnel diameters. The excavated face will be supported with lattice ribs, erected at a span ranging between 1.2m and 1.5m. Excavation will be followed by a layer of shotcrete, 100mm-300mm thick, reinforced with a steel mesh.
Also due to time constraints, the tunnel will be lined 300m behind the excavated face. This will continue until breakthrough, when the lining will be carried out in 2x12m sections per day.
The Dichalorematos tunnel, running through marl and clay, will be built from just one end using an excavator and loader. Excavation will be similar to the Knimidos tunnel, except in the more clayey ground where forepoling will be applied up to 12m ahead of the face. Following the bench excavation, a permanent concrete invert will also be cast.
The motorway extension is being built to avoid further congestion in popular tourist towns in the region. Tunnelling works will amount to about US$90M of the project cost, which is being jointly financed by the country’s public purse and the European Union support package.
