Ground penetrating radar application to determine the concrete volume in a tunnel

The vault damage in a railway tunnel, caused by damps in a granite massif, produced the granite slabs roof detachment. Sustitution of these granite slabs by concrete, including damping voids between the roof and the granite massif, was the most optimal solution concerning the preservation of the railway interior tunnel size (gallbo). The volume of concrete necessary to cover the vault and the gables of the tunnel was determined using a ground penetrating radar SIR 70 from GSSI, with a 500 MHz center frecuency antenna. Twelve radar profiles along the tunnel, covering the vault and the tunnel walls, were made to determine the total volume of concrete necessary to replace the old granite slabs, the void location and the identification of the tunnel region to be repaired. Ground penetrating radar measurements allowed to know the thicknesses of the granite slabs and the distance between these slabs and the massif rock of the irregular void