FACTORS AFFECTING THE BACKCALCULATION OF PAVEMENT CHARACTERISTICS BASED ON FFWD DATA

The evaluation of pavement structural condition is essential for ensuring safe operation, timely detection of defects, and informed decision-making regarding maintenance and rehabilitation. One of the primary and most effective methods for such assessment is the backcalculation of pavement layer moduli based on the results of testing with a Fast Falling Weight Deflectometer (FFWD). This method allows for indirect, non-destructive determination of the actual load-bearing capacity of pavement structures. Objective. To analyze the influence of input data — including specified thicknesses of structural layers, surface temperature during testing, type and duration of loading impulse, condition of interlayer bonding, and load positioning relative to deformation — on the results of backcalculated elastic moduli derived from FWD data. The paper examines key factors affecting the accuracy and reliability of backcalculation outcomes. Particular attention is paid to the role of input parameters such as modulus values, interlayer adhesion, weighting coefficients, as well as the influence of climatic conditions and the physical state of the pavement. A theoretical review of scientific and technical literature was conducted, alongside a synthesis of recent experimental studies. The impact of various factors — such as geometric characteristics of layers, temperature, surface and subsurface defects, measurement parameters, and data processing methods — on the accuracy of the backcalculated results is assessed. Variations in temperature, material heterogeneity, presence of cracks, ruts, voids beneath slabs, or poor load transfer conditions significantly affect deflection results and, consequently, the accuracy of computed moduli.