Identification of pavement elastic moduli by means of impact test

• Transformation of the dynamic displacements into static substitutes is presented.
• An original method for identification of pavement model parameters is proposed.
• Influence of the accuracy of the measurement on the identified values is analyzed.
• The proposed method has been experimentally validated on a newly built road section.

The practically important problem of identifying airport and road pavement model parameters by means of the falling weight deflectometer (FWD) is solved in this paper. The loads exerted by FWD have a momentary dynamic (impact) character, whereas the current computational pavement models (commonly used in practice) are static models. Dynamic models are used marginally due to their complicated mathematical description. As a result, in practice static model parameters (elastic moduli) are identified on the basis of displacements determined under a dynamic load (a force impulse), which creates an obvious methodological conflict. This paper presents a method of identifying the parameters of airport and road pavement models (in the form of multi-layered elastic half-spaces) on the basis of dynamic impulse test results, using a method of transforming the dynamic displacements into their static substitutes (i.e. the displacements which would be determined by a hypothetical static test). The presented solution makes it possible to identify model parameters for any shape of the distribution of the load (under the loading plate), approximated by a series of Legendre polynomials. The algorithm was subjected to simulation tests in order to determine the influence of the limited accuracy of the displacements yielded by the FWD test on the values of the identified parameters (elastic moduli). For this purpose randomly generated errors were added to the theoretically calculated displacements. The proposed method has been experimentally validated on a newly built flexible-pavement road section, by comparing the results yielded by it with the results of direct static measurements by means of the Benkelman beam. The results obtained by the proposed method were also compared with the currently most commonly used method which wrongly assumes that the static flexibility of a tested system can be approximated with a ratio of the maximum displacement to the maximum load, measured in the impact FWD test.