TUNNELLING PROBLEMS DELAY ATHENS METRO

The Athens Metro project, which began in November 1991, covers 17.6km, and is scheduled to be completed by mid-1999. This article briefly describes the project, and the very difficult construction problems that it met. These problems arose from continuously changing earth formations and archaeological discoveries in the old city, built thousands of years ago. As a result, the works were delayed, and many initial decisions about routeing and design had to be changed. Two underground lines have been commissioned, which will have 21 stations. Work is in progress at 45 locations throughout Athens, and all the stations are now under construction. The new lines will serve 450,000 passengers a day, and the existing 9.2km line, with 12 stations, serves 330,000 passengers a day. The underground rocks include igneous rocks and Athens schist. The tunnel construction methods being used are: (1) tunnel boring machines (TBMs) for 11.7km of double-track tunnels between stations; (2) the New Austrian Tunnelling Method (NATM) for 1.1km of six underground stations and various auxiliary tunnels; and (3) cut-and-cover for the other 15 stations, 6.5km of tunnels between stations, and 29 shafts. The first TBM has been halted due to difficult geology, and the second TBM has been stopped because of underground structures.