Evaluation of traffic speed deflectometer for collecting network-level pavement structural data in Tennessee

Due to the incompleteness of construction history and the resulting inaccuracy of pavement structure value, it is necessary to adopt innovative technologies to obtain accurate network-level pavement structural data in Tennessee. Recent technological advancements have resulted in the development of continuous deflection-measuring devices including traffic speed deflectometer (TSD). TSD can provide better spatial coverage and efficiency than static devices such as falling weight deflectometer (FWD) [1]. Since the first prototype device developed in Denmark in the late 1990s, TSD has been constantly evolving with new features, but the concept remains the same: for a semi-truck with a rear axle load of 100 kN (22 kips), a set of Doppler velocity-sensing lasers are mounted on a servo-hydraulic beam close to the rear axle to measure the deflection velocity of a loaded pavement [2]. Based on the measurements, the deflection velocities divided by the instantaneous vehicle speed give the deflection slopes. As shown in Figure 1, absolute deflections can be obtained by integrating the deflection slopes numerically or by using a closed-form solution of a mechanical model, such as an elastic beam on a Winkler foundation. Once the deflection bowl is obtained from TSD for a specific location, it can be compared with the FWD deflection bowl measured at the same location