Within the scope of “Istanbul - Ankara High-Speed Railway Project”, “Design and Construction Works Between Geyve - Sapanca (Dogancay Ripaji)”, there are a total of 8 tunnels including 2 main tunnels and 6 security tunnels. Of these, the T2 tunnel is located between Km: 127 + 930 and Km: 132 + 597 of the project. The T2 tunnel with a total length of 4667 m with a diameter of 13 m and the security tunnels (GT-4, GT-5 and GT-6) of the T2 tunnel with a total length of 2049 m are being carried out by one of our Holding companies ‘Soner Temel Mühendislik İnşaat ve Ticaret A.Ş’’ with a protocole of agreement dated February 17, 2020 and a subcontract dated March 2, 2020. Within the scope of the specified tunnels, site mobilization was completed at five different points, and work began on February 19, 2020. It has been determined a work period of 966 days (32 months) for the excavation-support, intermediate concrete lining with steel arches and final concrete lining works to be made within the scope of the Project. The T2 tunnel area, starting from Akçay Valley in the borders of Sapanca District of Sakarya and passing through Ilimbey and Karaçam quarters and ending in Doğançay sub-district of Geyve is within the North Anatolian Fault (NAF) system zone, which is the most important neotectonic period structure of the country and seismic zone. Therefore, during the excavation-support works, a certain seismic risk is taken into consideration. The rock class is defined commonly as C4 and the supporting and final lining systems resulting from the designs created according to the NATM project design criteria are applied.