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    A Pavement Evaluation Procedure Incorporating Material Non-Linearity

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    Two new computer programs, LEAD and FEAD, have recently been developed at Nottingham for the back-calculation of elastic stiffnesses of pavement layers from deflections measured with the Falling Weight Deflectometer (FWD). These programs represent a significant improvement on the program PADAL, previously developed at Nottingham. A revised algorithm for the iterative back-calculation process, based on the Gauss-Newton method, has been successfully implemented. Appropriate stress-strain relationships for the granular layers and the subgrade were built into the programs, enabling the non-linear behaviour generally exhibited by these materials to be evaluated. The influence of overburden, pore pressures and “locked-in” horizontal stresses on the in situ stiffnesses is also considered. Additionally, a rigid bottom may be included in the analysis. The main difference between the two codes is in the sub-routines adopted for the computation of deflections. LEAD makes use of layered elastic analysis, while FEAD uses a finite element approach which, although more accurate for non-linear problems, is more time consuming. Data from FWD surveys have provided a means of validating the new software. Examples are presented, including comparisons with laboratory test data. The results suggest that the stress-dependent nature of the lower layers can be of significance for the overall behaviour of the pavement.


    elastic stiffnesses, deflections, non-linear models, back-calculation algorithm, FWD data, validation

    Author Information:

    de Almeida, JR
    Research assistant, University of Nottingham, University Park, Nottingham

    Brown, SF
    Professor, University of Nottingham, University Park, Nottingham

    Thom, NH
    Lecturer, University of Nottingham, University park, Nottingham

    Committee/Subcommittee: D04.39

    DOI: 10.1520/STP18150S