The Dogancay T1 tunnel, projected within the scope of the Ankara-Istanbul high-speed train project, is being excavated entirely through clay and cohesionless units and is located in the North Anatolian Fault Zone (NAFZ). To determine the support system in the tunnel, innovative approaches require investigation through analytical and numerical methods to evaluate their suitability. The present study investigates rigid support systems, including the intermediate lining and pre-support excavation techniques in the new Austrian tunneling method (NATM), with 3D numerical analyses. The tunnel is in a seismically active zone, and the study also addresses the seismic sustainability of the proposed support system. The results of analyses showed that the proposed excavation and support system can be successfully implemented in the Dogancay T1 tunnel. The case study provides guidelines for investigating tunnel excavation and support systems in poor ground conditions in tectonically active zones.