Evaluating Falling Weight Deflectometer Back-Calculation Software for Aircraft Pavement Strength Rating

In recent years, software has been developed to calculate aircraft pavement strength ratings from modulus values that are back-calculated from deflections measured by a falling weight deflectometer. Deflection data from a uniform section of consistent runway pavement was analysed for variability to determine the effect of deflection variability on back-calculated modulus and the resulting pavement strength rating. The drop force of the falling weight had a significant influence on the calculated pavement strength, with 50 kN drop force rating the pavement approximately 35% lower than the 100 kN drop force. The number of layers in the nominated pavement structure also had a significant influence on the back-calculated modulus values, but not the resulting pavement strength rating. Compared to traditional design-based evaluation using intrusively measured layer thicknesses and laboratory material characterisation, the falling weight deflection back-calculation underestimated the pavement strength. Consequently, it is recommended that airports do not set their PCN based on back-calculated FWD data unless also supported by intrusive geotechnical investigation and a design-based evaluation.