The experience of several researchers in using back-calculation programs showed that the predicted moduli may vary for each program. Also, inappropriate seeds, given as initial values to iterative procedures, occasionally led to suspicious solutions, since they appear to have no physical meanings. The conclusion was that it is necessary to use engineering jdgment to ensure that the calculated moduli are reasonable. The objective of this paper is to present the influence of the thickness input, not only on the pavement and the subgrade moduli, but also on the final overlay results. This is done by analyzing in detail a recent local taxiway evaluation project, with two different program codes (NOALIV and SAASHTO) for a fixed, two-layer model.
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