**1. Introduction**

Today, the number of tunnel projects has increased significantly due to the developing infrastructure projects. Tunnels are used in most large highways, railways, water, metro and mining projects. Depending on the increasing number of infrastructure projects, the total number being constructed is gradually increasing. As a consequence of this increase, tunnel design and construction works are also gradually increasing. Project design studies carried out after the determination of project routes are of great importance. It is extremely important to determine the rock and ground support classes, excavation methodology and support elements within the project design studies. Although there are different tunnel project approaches today, all designs are based on the principles of rock and soil mechanics; for this reason, the correct determination of soil and rock parameters is the main factor in determining tunnel design. In addition, the correct realisation of the geological model of the route through which the tunnel will pass is another factor that will directly affect the tunnel design. In addition to all of these, surface structures also affect the design. While deformation is not allowed in tunnels to be excavated under towns and cities, a certain amount of deformation is allowed in mountain tunnels. The design of the support system is affected by natural structures such as streams on the surface. This design effort can be divided into empirical, analytical and numerical methods for the project work to be done. Although these three methods are used separately most of the time,

they should be evaluated together for a healthy tunnel project. During the tunnel excavations, tunnel projects should be compared with predicted and encountered geological conditions. If necessary, tunnel projects should be revised according to the encountered geological conditions. It should be well known that the predicted geological conditions and the actual geological conditions encountered will never be the same. For this reason, geotechnical measurements such as geological face maps, convergence measurements and deformation measurements should be made during the tunnel excavation in order to make the necessary revisions and updates. If necessary, the support system and rock mass parameters should be revised with a back-analysis. In addition, laboratory tests made from the boreholes taken during the excavation and rock mass parameters should be re-evaluated.
