Numerical investigation of pavement responses under TSD and FWD loading

The Traffic Speed Deflectometer (TSD) overcomes the limitations of the Falling Weight Deflectometer (FWD) in terms of traffic interruption and testing inefficiency, thus has been used for network-level pavement structural evaluation. However, compared to FWD, which has accumulated plenty of data and comprehensive evaluation methods over decades, the applicability of TSD is yet to verify. It is imperative to compare pavement responses under TSD and FWD to validate the applicability and substitutability of TSD. Based on the difference between TSD and FWD in loading characteristics and asphalt concrete (AC) properties, six 3D-Move models were established successively to explore the influence of different testing factors on pavement responses. The simulation results show that under the same load magnitude, peak deflections and peak strains caused by TSD were always greater than that of FWD due to the lower equivalent load frequency of TSD. Compared to the peak deflection, the deflection basin shape of TSD was more sensitive to the dynamic effects and the viscoelasticity of the AC layer. Besides, AC viscoelasticity and damping caused the lag in TSD deflections and strains. In the layer modulus back-calculation from TSD deflections, the dual circular load and dynamic effect of TSD were crucial, but the AC viscoelasticity could be neglected. The use of FWD-based programs to back-calculate the layer modulus from the TSD deflection would result in a stiffer AC layer and a stiffer subgrade.