Europe
Greece
History
The first subway line in Athens – and its only subway line until 2002 – dates from 1930. At the time, the population of the city was 450,000. That figure has since swelled to 3,500,000 – of whom 900,000 live in central Athens. Traffic has kept pace with the growth in population, resulting in congested roads throughout the city.
In 1987, a call for tenders was launched to build Lines 2 and 3. It was only in 1991 that a contract between Greece’s ministry for public works and the European consortium Olympic Metro (bringing together 22 Greek, German, and French firms) was signed.
Work began in November 1991 and, according to the contract, should have ended in 1997. However, a series of unforeseen circumstances held the worksite back for during several months.
Technical details
The project called for the construction of two subway lines over a seven-year span: a 9.2-km north-south line; an 8.4-km east-west line; and 21 stations. Initially, two tunnel-construction methods were selected: TBM-assisted excavation for the most part and NATM (New Austrian Tunnelling Method). Unfortunately, geological and organizational problems disrupted the established work program, resulting in delays.
As a result of multiple tectonic shifts, the Athenian subsurface soil is complex. Initial estimations, which served as a starting point for the project, proved to be inaccurate. Two years of further study were needed to establish a reliable assessment of the area’s subsurface properties for the purpose of excavation. In general, Athens schists (or levels of sedimentary subsoil) offer good cohesion, but other subsoils in the area offer much less uniform hold, which resulted in rock slides along the first TBM’s excavation path and a slowdown in the tunnel-boring process.
Athens has been continually inhabited over the last 9,000 years, with successive eras of its history preserved in incremental layers of subsoil. The subway lines run below the historical heart of the city. Accordingly, many precautions were taken to prepare for the passage of the TBMs below, or in close proximity to, historical monuments. In the process, archaeological sites were uncovered, notably a Roman bath in perfect condition with its water basin and heating system embedded in the floor. These discoveries were excellent news for the city, but they did slow down work.
Regional development
The project’s main objective was to reduce traffic congestion in Athens by opening up a new, quick transportation channel connecting the old town, business district, and residential sectors. Subway traffic frequency at peak hours is one train every three minutes travelling at 80 km/hr.
Extending the Athens subway was also designed to reduce significantly the emission of pollutants that harm the city’s archaeological sites. Another goal was to shorten travel time within the city. On average, travelling by car from Dafni, at the southern terminal of Line 2, to downtown requires 30 to 45 minutes; on the subway, the same journey only takes 9 minutes.
Construction of the two tunnels has entailed comprehensive archaeological digs that have uncovered numerous sites of historical interest. The art objects that were uncovered continue to be present even after the end of the project. Indeed, three stations feature modern or antique art displays.
Key figures
Total cost: €851 M
Work dates: November 1991 to December 2002 (133 months)
Excavation: 2,500,000 m3
Total concrete volume: 7,000,000 m3
Reinforcing steel: 45,000 t
Number of TBMs: 2 (Styx and Persephone)
TBM diameter: 9.5 m
Length of TBM: 140 m
TBM rotation speed: 0 to 4 revolutions per minute
Length of platforms: 110 m
Length of Line 2: 9.22 km
Length of Line 3: 8.38 km
Total track length: 43.2 km
Electrical feed: 750 V continuous current with a third rail
Surface of the depot: 120,000 m2