The design of great infrastructures is often complicated by the presence of complex, or sometimes uncertain, geological settings, which require a detailed study of the Geological Reference Model (GRM) reconstruction. For this purpose, however, site investigation, mainly represented by drillholes completed with field and laboratory tests, being punctual and not continuous along the project, could reveal themselves insufficient, especially without sufficient information, from surface geology, useful for the reconstruction of the Geological Reference Model. In such cases, they may be accompanied by geophysical surveys linear (seismic refraction and seismic tomography bases), for which surveys will act as "trimming elements" of the geophysical results. As said occurred during the design, operated by "Design and Construction Management" of ANAS, of a road axis in Sardinia, characterized by the presence of a 150 m long viaduct, the Serra viaduct, falling in a rather complex geological-structural situation.