Agreement of FWD and TSD measurements

Abstract: Non-destructive testing, such as deflection measurements, is vital in evaluating pavement structural behaviour and capacity. The Falling Weight Deflectometer (FWD) is the most widely used deflection measuring device in the world. However, it poses some limitations, particularly in high-mobility routes, where traffic accommodation measures must be implemented during testing. The latest developed deflection measurement technologies include Traffic Speed Deflectometer Devices (TSDDs), comprising of moving deflectometers or continuous deflection measurement devices, which include the Traffic Speed Deflectometer (TSD), Rolling Wheel Deflectometer (RWD), and Rolling Dynamic Deflectometer (RDD). The TSD offers, advantages, taking continuous measurements while travelling at speeds of 80 km/h, minimizing traffic disruptions, especially on high-mobility routes. Regarding the deflection testing, the FWD applies the load using a circular plate with a standard 40 kN load, while the TSD applies a load using two rear dual tires of 20 kN each (totaling 40 kN). Maximum surface deflections, lower layer index (LLI), middle layer index (MLI) and base layer index (BLI) are four important surface parameters or indices that are used to evaluate pavement behaviour in benchmarking analysis. The study presented in this paper employs two statistical methods ( limit of agreement and analysis of variance), to assess the agreement between FWD and TSD measurements. The paper further simulates the FWD and TSD loads on granular pavement structures by using software for mechanistic-empirical design and General Analysis of Multi-layered Elastic Systems (meGAMES) to evaluate the surface indices. Through correlation analysis, this study proposes reduction factors to facilitate the use of TSD-based condition rating criteria, similar to FWD-based criteria, for pavement structures with granular base and subbase layers.