Water in tunnels represents a challenge in any geological condition. When dealing with cohesive
material, this aspect might bring additional problems linked to the low permeability, which does 
not allow effective and quick drainage to stabilize the ground around the tunnel. Ordinary draina-
ge systems are an effective method, especially in higher permeability grounds, but these are losing 
efficacy in soft clays. This paper 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. The advantage of this technique is not only a decrease in the pore water pressure but also an 
increase of cohesion and elastic modulus over time thanks to the induced consolidation process of 
the clay and a consequent improvement of the mechanical characteristics. Water in tunnels represents a challenge in any geological condition. When dealing with cohesive
material, this aspect might bring additional problems linked to the low permeability, which does 
not allow effective and quick drainage to stabilize the ground around the tunnel. Ordinary draina-
ge systems are an effective method, especially in higher permeability grounds, but these are losing 
efficacy in soft clays. This paper 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. The advantage of this technique is not only a decrease in the pore water pressure but also an 
increase of cohesion and elastic modulus over time thanks to the induced consolidation process of 
the clay and a consequent improvement of the mechanical characteristics.