GPR PERFORMANCES FOR THICKNESS CALIBRATION ON ROAD TEST SITES

Abstract This paper presents ground penetrating radar (GPR) experiments conducted on a number of road test sites. In its capacity as a State civil engineering research organization, the Laboratoire Central des Ponts et Chaussees (LCPC) possesses large-scale testing facilities, such as a circular pavement fatigue test track, ideal for road-related research. This particular facility is composed of several sections of different known structures especially well-adapted for GPR investigations. Our study of GPR techniques made use of a commercial system for measuring asphalt layer thickness. Various road structures have been examined with a GSSI system. Cores have been drilled and permittivity measurements performed in the laboratory. The initial study reveals a comparison between thickness measured by coring and that calculated from both measured permittivities and GPR-selected times. A second study has consisted of avoiding calibration with core drilling, by means of recording GPR signals with a non-destructive testing technique on the multi-layer structures (i.e. common middle point). A numerical reconstruction has then been developed in order to calculate the thickness and velocity of each layer from experimental data. When compared with the cored samples, results show a sufficient level of accuracy in the first two or three layer thickness measurements to satisfy the needs of road facility managers.