Complementary Pavement Subsurface Assessment Using Mobile Acoustic Subsurface Sensing And Ground Penetrating Radar Systems

Pavement subsurface condition inspection is critical for transportation infrastructure health assessment. Mechanical properties, layer picking and de-bonding/voids detection are of specific interest. Previous research work either measured mechanical properties using acoustic surface waves methods in a slow contact sensing way, or detected pavement layers with a commercial Ground Penetrating Radar (GPR) system. This presentation explores a joint analysis of pavement subsurface properties using two subsurface sensing systems, a Mobile Acoustic Subsurface Sensing (MASS) and an air-coupled GPR with innovative design. MASS measures the near-surface radiating surface waves excited on the pavement with sound enclosed directional microphones. The radiating surface waves carry the pavement profiles information of mechanical properties as elastic modulus through dispersion features. The dispersion curve could be accessed rapidly through acoustic signal processing such as windowing, filtering and spectrum analysis. The challenge is the rapid inversion for irregular pavement profiles with no prior knowledge of layering. GPR is able to collect reflected electromagnetic signal from the interfaces of different layers with dielectric contrasts. Layer boundaries can be estimated by cross correlation with transmitted signal such that we can get the traveling time of radar signal within different layers. As well, the velocity of radar signal within each layer can be calculated from reflection coefficient by deconvolution. Therefore, we can identify the thickness of each layer of pavement. This work presents the joint analysis of complementary MASS and GPR measurements. First the layer boundaries are determined from the GPR data. This information is used as starting values in the acoustic inversion determining the mechanical properties. Results show improved inversion results using the GPR layer information. The subsurface assessment can be achieved rapidly in a mobile dual system strategy. This joint NDT strategy would supply an alternative solution for faster assessment for pavement subsurface with both thickness and stiffness profile.