Owing to the increase in population, transportation has become one of the major research topics. Among existing transportation systems, railway is one of the most economic and fast systems, and therefore, there has been an increase in new railway constructions in recent years. In Turkey, the longest railway tunnels, the Bahce-Nurdag high-speed rail tunnels, are under construction in the southern part of the country. This twin tubes tunnels are approximately 10 km in length, and they are excavated using tunnel boring machines (TBM). The tunnel route locates in the East Anatolian Fault Zone and the portal region is composed of debris and old landslide deposits. For this reason, mitigating the potential landslide hazard is critical for the tunnel. Therefore, the present study investigates the TBM tunnelling-landslide relationship by employing 3D numerical analyses. The analyses show that the last 600 m of the tunnel has a potential landslide hazard and some additional measures should be considered along this part to ensure tunnel safety. The tunnel conditions are highly complex, and thus it is an interesting case for tunnel engineers.