Ground Information and Selection of TBM for the Thessaloniki Metro, Greece

Abstract

The Thessaloniki Metropolitan Railway is currently at its primary construction stage. The railway is composed of two separate similar to 6-m-diameter parallel tunnels, each of which is similar to 8 km long and has 13 stations. The span between the tunnel axes is approximately 12 m, and the depth of the red line (track level) varies from 15 m to 30 m. The geology of the urban area of Thessaloniki is characterized by the presence of Neogene and Quaternary deposits. The base formation for the study area is a very stiff to hard red clay, dating to Upper Miocene-Pliocene time. On top of this formation, Quaternary sediments have been deposited, most of which consist of sand and/or gravel in a clay-silt-dominated matrix, covered in places by anthropogenic fill. Ground investigation campaigns have incorporated a significant number of sampling boreholes and in situ and laboratory testing. In this study, data from borehole loggings, particle-size analyses, natural moisture content, Atterberg limits, permeability tests, pressure-meter tests, cone penetration tests (CPT), and standard penetration tests (SPT) were analyzed in order to obtain a better geological understanding, a geotechnical zonation, and a classification of the ground with respect to mechanized tunneling. The characteristics and parameters of the soils and the hydrogeological regime indicate that an EPBM (Earth Pressure Balance Machine) rather than a slurry TBM (Tunnel Boring Machine) should be used for the tunnel construction.