ABSTRACT
Monastiraki Station is a complex Athens Metro Station, at the historical centre of Athens, near the Acropolis ancient monument. At this point there is a cross section of two different metro lines, the oldest one line 1 that exists since 1895 and the new line 3. The new tunnel line 3 passes below the oldest one and there is no connection between two tunnel lines. The connection between two lines is implemented trough an intermediate building that lies near the main station structure. The station includes a main tunnel wherethe temporary structure was constructed under an umbrella of microtunnels because of difficult construction conditions and weak soil. The need to use microtunnels came from the very soft surrounding rockmass causing large surface settlements, about 90mm, during the excavation of the cross- over access tunnel of the station. Purpose of the design was the surface settlements reduction and the safety of temporary supporting lining, in the Main Tunnel underground excavation construction stages. The most important scope of the design, was to restrict surface settlements, at the very densely populated area of Monastiraki. For the design of the tunnel temporary lining with microtunnels, a 2-D finite element model is used, containing the cross section of the temporary lining and the surrounding soil up to the ground surface. A non-linear elastoplastic analysis is applied by the introduction of a Mohr – Coulomb failure criterion for the soil plane Finite elements. The whole application was successful and the limiting of settlements, under serviceability conditions, was achieved. During the construction, the provisions of the study were verified to a very large extent, with a deviation that does not exceed 5%.
