2012 | ONGOING
The Haidari–Piraeus extension of Athens Metro Line 2 stretches from Haidari, a residential district located in the western outskirts of the city, as far as the Port of Piraeus, ending at Dimotiko Theatro station. The project involves the construction of six new stations: Agia Varvara, Korydallos, Nikaia, Maniatika, Piraeus, and Dimotiko Theatre. The first three were inaugurated on 7 July 2020 with Prime Minister Mitsotakis and the Minister of Infrastructure and Transport Karamanlis in attendance.
Once completed, the new section of the Metro will be capable of transporting 135,000 passengers a day and will connect the main Greek port with Eleftherios Venizelos International Airport, reducing travelling time by 60 minutes. There will be an average of 23,000 vehicles less circulating per day, with a daily reduction of around 120 tonnes of CO2.
The contract included the excavation of a 6.5-kilometre-long dual-track tunnel using a Tunnel Boring Machine (TBM), a machine capable of excavating tunnels in a mechanized way and in complete safety. TBMs, commonly known as “moles”, excavate the rock with a rotating cutting wheel equipped with cutters. These remove the excavated material, and line the tunnel that was just made by installing prefabricated segments. The model chosen for this particular task is an Earth Pressure Balance (EPB) measuring 9.48 metres in diameter: a perfect model for excavations in an urban setting because it does not cause the overlying surface to collapse.
The TBM, called Hippodamus in honour of Hippodamus of Miletus (a fifth-century BC Greek urban planner who was commissioned to build the Piraeus after the Persian Wars), started its journey from the launch shaft in the Haidari neighbourhood, in a building site area that was smaller in size, where the machine was lowered and assembled 35 metres below the surface.
Hippodamus crossed one of the most ancient cities in the world, one with a very high population density and highly heterogeneous urbanization. Besides having travelled underneath working railways, sewerage systems, and pipelines, which made the operation particularly hard to carry out, the excavation of the tunnel also came across a large number of archaeological ruins.
The excavation of the new stations led to the discovery of an as yet unspecified number of archaeological finds dating back to ancient Athens, among which vases, amphorae, dishes, statuettes, and other items that were then catalogued and archived by a group of expert archaeologists and specialists.
One of the most difficult technical aspects arose in the section of the tunnel after Piraeus Station, in a stretch about 100 metres long, situated 15 metres below sea level: the docks and the foundations of a 20-storey building are no more than 30 metres away. There the excavation work required the implementation of a very rigid and demanding procedure, with continuous and detailed monitoring to ensure its successful completion.
Hippodamus completed its work on 27 January 2018, achieving the final breakthrough about 4 years after the start of the excavation. The tunnel was lined with over 30,000 segments. The project involved around 500 workers and technicians overall.
Boring the ground under the city of Athens has been a continuous excitement and gratification for all the people involved.
A significantly wide range of geomechanical features, an intensly urbanised area, archeological or more recent pre-existences and working below the water table in very close proximity to the harbour; dealing succesfully with all those challenges, the tunnel extension of the Metro Line 3 is being completed with state of the art quality and absolute satisfaction of the stakeholders.
We are all glad and proud.
Eng. Michele Petris, Tunnel Manager