A Small-Strain Hypoelastic Constitutive Model and Application to Foundation Field Tests for Initial Stiffness Evaluation

The small-strain stiffness of soil measured through dynamic tests can be utilized in the finite element method to simulate static conditions. Although numerous soil constitutive models incorporated the elastic law of the maximum shear modulus and normalized shear modulus degradation curves to simulate the small-strain behavior of soil, rare models can be calibrated using the normalized shear modulus degradation curves measured from the resonant column and torsional shear tests varying a wide range of mean effective stresses. The poor calibration of the elastic law in the soil constitutive model may result in uncertainties when simulating the initial stiffness of the foundation in finite element modeling. The current study developed a small-strain hypoelastic model based on normalized shear modulus degradation curves using four material parameters that provide greater flexibility in controlling the curvature shape of the degradation curves. The small-strain hypoelastic model was evaluated using an element test and applied to a settlement test on a shallow foundation, a laterally loaded test on a slender pile, and a series of laterally loaded tests on monopiles. The results indicated that the reference strain and curvature parameter in the empirical equations for the normalized shear modulus degradation curves should be related to the mean effective stress, and the curves should be carefully calibrated by using resonant column and torsional shear tests under low mean effective stresses. The calibrated hypoelastic model significantly improved the accuracy of predicting the nonlinear initial stiffness in finite element modeling. The suggested procedure of calibrating the small-strain hypoelastic model was proposed to provide guidance in various engineering practices.