Numerical and Optimization Techniques Applied to Surface Waves for Backcalculation of Layer Moduli

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Abstract
This paper eontains two methods of determining the pavement moduli and thicknesses using a computer prograrri written in FORTRAN 77. The first method, a simple finite difference technique, is developed for the analysis of generalized Rayleigh waves in multilayered elastic media. The method, which leads to an eigenvalue problem, is very effective in determining theoretical dispersion curves for pavement systems modeled as layered composite plates with free surfaces at both top and bottom or free surface of the top and rigid base at the bottom. Backcalculation of moduli and thicknesses is done by an optimization routine developed by Powell [1] based on least squares criterion. The second method determines a theoretical dispersion curve based on Knopoff s technique [2]. Since phase velocities of the waves observed experimentally on pavement structures are complex, suitable modification of Knopoff's algorithm for the geologic model has been made by the authors to account for this effect. For optimization, the same technique is used as mentioned above. Numerical results obtained in the two cases show excellent agreement with previously published solutions obtained by other theories.

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