Tunneling in a saturated environment and the intrusion of groundwater flow into tunnels during excavation is one of the most serious problems in tunneling projects. Water ingress into the tunnel can lead to damage to tunnel construction equipment, personnel, the excavation process, etc. The hydrogeological studies of the springs along the tunnel route and the estimation of the water entering the tunnel also investigate the possibility of drying up or reducing the water level of the tunnel route. The hydrogeological studies of the springs along the tunnel route and the estimation of the water inflow into the tunnel will also examine the possibility of drying up the springs or reducing the water level of the tunnel route. On the other hand, the complications of water ingress into the tunnel and the lack of an accurate and appropriate method increase the importance of these studies. Experimental and analytical methods are available to predict water inflow into a tunnel. In this article, in addition to presenting the general process of carrying out hydrogeological studies of tunnels, the weight percentage of hydrogeological studies and the problems associated with them are discussed. On average, more than 30% of all tunnel problems are related to groundwater, but less than 5% of studies are carried out in this field. The disproportionate weight of the above two cases and its causes are among the other cases discussed in this article.
