**10. Conclusion**

Empirical, analytical and numerical approaches should be used together in tunnel design. Empirical methods provide preliminary information for the rock mass and support design during the design phase. The details of support systems should be complemented by numerical analysis.

Each tunnel reaches its final design status during the process of tunnel excavation. All the acceptances made during the design phase should be considered as preliminary assumptions. Based on the geological-geotechnical research carried out during the design phase, the tunnel behaviour cannot be fully revealed. For this reason, measurements such as geological and geotechnical evaluations, deformation measurements, convergence measurements and pressure cells should be done to revise the tunnel design according to the encountered geological conditions.

During the tunnel excavation, geological-geotechnical measurements, face maps and horizontal boreholes, if necessary, should be carried out continuously.

TBM selection and design are completely dependent on geological conditions. The wrong TBM selection can be made because of the geological profile that is not determined correctly. This situation causes very serious project problems in the tunnel.

While determining the tunnel excavation method, tunnel opening and ground conditions are some of the most important factors. In large-diameter tunnels, the tunnel is usually divided into top heading, bench and invert if necessary. It is obligatory to close the ring (top heading, bench and invert) as soon as possible when excavating in weak rock conditions and soils. Otherwise, serious deformations can be observed in the tunnel. The most correct approach for tunnel section is circular or near-circular type section.
