Dynamic Backcalculation Approach of Deflections Obtained from the Rolling Dynamic Deflectometer: Fundamental Theory

In this study, the dynamic behavior of asphalt pavement from the Rolling Dynamic Deflectometer (RDD) was investigated. The effect of the loading frequency to the RDD deflections was evaluated by conducting RDD tests on several road sections. Stationary RDD tests were done to measure the forced and free vibration response of the pavement in which steady-state and decaying response signals were observed. It was found that aside from calculating the peak-to-peak deflections from the RDD forced vibration, the pavement's natural frequency and damping ratio can be determined from the RDD free vibration response. To verify whether the measured natural frequency and damping ratio represent the dynamic response of the pavement system, a frequency sweep response (FSR) test was conducted. First, the repeatability of free vibration testing was studied by evaluating the measured responses at different locations. Then, a steady-state vibration equation was used to predict the response of the pavement system from a sinusoidal loading using the damping ratio and natural frequency measured in the field. The measured deflections from field FSR testing showed a good correlation with the predicted response, suggesting that the measured natural frequency and damping ratio represent the pavement at a unique stiffness parameter, k .