ABSTRACT: In recent years, transportation tunnels have been excavated by mechanical methods. The selection of a suitableexcavator for the geological structure is an important factor in achieving an efficient tunnel excavation. For thispurpose, geological formations along the Kabataş-Mecidiyeköy tunnel alignment have been evaluated in terms ofexcavation mechanics. The Istanbul Metro Project between Kabatas-Mecidiyekoy stations includes two types oftunnel excavations, tunnel boring machines (TBM) and New Austrian Tunneling Method (NATM). The total length ofthe two lines of the tunnel to be opened using TBM is 6180 m. In addition, the total length of the two lines to be openedby NATM method is 4490 m. In this study, soil and rock units along the Kabataş-Mecidiyeköy tunnel alignment wereclassified in terms of engineering geology, and tunneling, and the effects of difficult ground conditions on tunnelexcavation were investigated. In addition, the related information is given for the permeability of the geological unitsand the groundwater level.