A Geotechnical Perspective on a Complex Geological Environment in a High-Speed Railway Tunnel Excavation (A Case Study from Türkiye)

The T26 tunnel was designed within the scope of Ankara-Istanbul high-speed railway in accordance with speed 250 km/h. Some serious problems and excessive deformations were encountered during excavation works. caused subsidence on surface Tunnel Boring Machine (TBM) became stuck; therefore, works suspended. Design for re-excavation extracting TBM carried out re-designed by New Austrian Tunneling Method (NATM) system. main purposes present study are to describe discuss sources problems. advantages disadvantages NATM methods having difficult ground conditions discussed. Critical points needing be considered tunnels excavated through weak effect selection process Considering complex geological geotechnical structure route, it is possible say that case an interesting engineering. Along landslides, high seismic activity, groundwater conditions, extremely rock mass features coexist. Therefore, route a very environment. However, due geometric limitations railways, relocation not possible. experiences gained from excavations under capable bringing new horizons future tunneling studies.