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A layered elastic theory approach to the calculation of the allowable load-carrying capacity and required overlay thickness of a pavement requires the values of the static elastic moduli of the pavement layers and the subgrade. A method is developed for determining the subgrade Young's modulus by vibratory nondestructive tests performed on the pavement surface. The response of pavements and subgrades to dynamic loadings is nonlinear, so that a nonlinear dynamic model of pavement response was developed by which the subgrade Young's modulus can be obtained from the measured dynamic pavement response data. The value of the subgrade Young's modulus predicted by vibratory nondestructive field tests was checked by laboratory dynamic resilient modulus tests. This was done by developing a nonlinear theory of the dynamic resilient modulus test by which the Young's modulus of the subgrade soil sample can be extracted from the resilient modulus test data. (Author)