STP1026

    On Transforms and the Dispersion Computations Used for Evaluating Layer Properties

    Published: Jan 1989


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    Abstract

    Computations of the dispersion of waves propagating through a layered pavement structure are fundamental to the determination of moduli for individual layers by what is called the wave propagation method. Processing field data using the Fourier transform is shown to lead to incorrect results that are generally inadequate for distinguishing among the multiple limbs of layered structures. The protocols for a new transform and dispersion analysis based on the cross-correlation operation have been defined and the transform has been programmed. Used in conjunction with pattern recognition methods applied “by hand,” the new method was tested with data from a well-defined laboratory model composed of encapsulated layers of sand with different moduli corresponding to different levels of vacuum. The results indicate that the method is capable of identifying at least as many as three layers in a structure. A prototype, rule-based and with totally automatic computation, has been demonstrated and holds promise. The new method calls for data collection at higher frequencies than before, and computation time is increased considerably. The significance of the work extends outside this area of research.

    Keywords:

    layered media, pavement structures, wave propagation, dispersion, Fourier transform, phase, cross-correlation transform, pattern recognition, rule-based, expert systems, layered sand model


    Author Information:

    Douglas, RA
    Professor, graduate research assistant, and professor, North Carolina State University, Raleigh, NC

    Eddy, JL
    Professor, graduate research assistant, and professor, North Carolina State University, Raleigh, NC

    Wahls, HE
    Professor, graduate research assistant, and professor, North Carolina State University, Raleigh, NC


    Paper ID: STP19834S

    Committee/Subcommittee: D04.39

    DOI: 10.1520/STP19834S


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