The excavation of tunnels under the water table has always represented a challenge in any geological condition, particularly when dealing with fine-grained soils, or more in general when the presence of fine rules the permeability and consequently affects the consolidation process, strictly connected with the stability of contour and tunnel face over the time. Ordinary drainage systems are an effective method, especially in high permeability grounds, but these are losing efficacy in soft clays. This thesis focuses on an innovative technique for stabilizing the tunnel face and surrounding ground by using a special soil nail consisting of a fiberglass bar element and an external sheath devised to contain the injected grout, which can also be integrated with a coaxial drain.