Verification and Analysis of the Pavement System Transfer Function Based on Falling Weight Deflectometer Testing

The falling weight deflectometer (FWD) test is a prevalent non-destructive testing (NDT) technique in engineering that is essential for evaluating pavement conditions. In this work, the transfer function (TF) theory in frequency domain analysis was applied to address the technical challenges present in FWD research. A pavement system transfer function (PSTF) was proposed as a novel approach for evaluating pavement conditions. The spectral method with fixed-end boundary conditions (B-SEM) was employed to compute the theoretical deflection data for different pavement structures with bedrock during FWD testing. The fast Fourier transform (FFT) technique was used to convert the data into the frequency domain, enabling the construction and calculation of the PSTF. The validity of the PSTF theory was confirmed, and the pavement information contained in the PSTF spectrum was discussed. An analysis and summary are conducted on the impact of variations in pavement attributes on the spectrum. The results indicate that the proposed PSTF contains information regarding pavement system, including the structural layer modulus, structural layer thickness, and bedrock depth. The pavement conditions can be evaluated by directly analyzing the PSTF without considering external factors. The PSTF spectrum is most significantly influenced by bedrock depths between 200 and 500 cm. For every 50 cm variation in bedrock depth, the coefficient of increase and decrease (CIE) of peak frequency ranges from 8.1% to 23.1%. The PSTF spectrum is highly sensitive to variations in the subgrade modulus between 40 and 70 MPa. In this range, the CIE of peak amplitude is greater than 11% for every 10MPa variation in subgrade modulus. The impact of the modulus and thickness of both the surface layer and base layer on the spectrum is noteworthy and should not be disregarded. Spectral analysis is used to summarize the variation in pavement attributes within the PSTF spectrum, serving as a theoretical foundation for further investigations.