Permittivity Heterogeneity Influence of Multiphase Pavement Materials on Ground-Penetrating Radar Detection Results: A Study Based on Probability Distribution

For ground-penetrating radar (GPR) detection, multiphase heterogeneous pavement models were built and on-site detections were conducted. The statistic distribution rules of relative permittivity in pavement materials including asphalt mixture and cement-stabilized macadam were determined, and the heterogeneous error correction method of the layer thickness and distress buried depth were studied. The heterogeneous interferences in the A-scan curve before and after interlayer reflection wave filtering were quantified. The relationship between the crack width and homogeneous reflection wave was proposed, and the heterogeneous interference on the identification of the internal crack in the surface layer was discussed. The results show that the relative permittivity values of the surface and base layers obey Gaussian distribution obviously. Heterogeneous error formulas of the layer thickness and distress buried depth were proposed, and the concept of assurance rate was introduced in the error correction. The heterogeneous interference ratio (HIR) index was proposed to represent the heterogeneous interference in A-scan curves, and its Gaussian distribution characteristics were put forward. The heterogeneous interference increases with the wave frequency increase, and the standard deviation of HIR in the surface layer is higher than that in the base layer because of its finer gradation. The average value subtraction method filters the interlayer boundary reflection wave, which has no or minimal influence on the mean value and standard deviation of HIR, respectively. The crack interference ratio (CIR) index was proposed to quantify the heterogeneous interference on the crack reflection wave. Higher wave frequency, wider crack width, and higher water content of the crack medium are conducive to decrease the heterogeneous interference on the crack identification. The reflection waves of the millimeter-scale internal cracks have close magnitude compared with the heterogeneous interference wave, so filtering the heterogeneous interference wave is the premise to identify the millimeter-scale internal cracks in the surface layer.