Evaluation of FWD data for determination of layer moduli of pavements

Falling weight deflectometer (FWD) testing has been done extensively in the past to assess structural condition and determine the moduli of pavement layers. The set of modulus values for pavement layers obtained from the backcalculation process may not be accurate even though the computed and measured deflection basin may match within tolerable limits. Extensive interpretation is involved in obtaining the layer moduli of these pavements. Guidelines and tools are provided for calculating layer moduli for flexible pavements. FWD interpretation has become increasingly challenging because more and more of our roads have experienced multiple milling operations and overlays. The characteristics of the structure such as damaged layers, thickness variation, and temperature changes can overwhelm the deflection data, having a far more significant effect than those induced by structural layer stiffness. This study emphasizes that proper interpretation of FWD data involves a complete evaluation of all available data, including core data, roadway data, and section-specific distress information. Evaluating multiple FWD measurements along the sections allows for the evaluation of consistency and assures reasonableness of interpretation.