Estimation of the Coefficient of Subgrade Reaction using Small-Strain Stiffness

Subgrade reaction modulus (Ks) is a conceptual relationship between soil pressure and deflection, which is widely used in structural analysis of various foundations. Values of Ks are assessed by relating them to intrinsic parameters of soil such as elastic modulus (Es) and California bearing ratio (CBR). The small-strain stiffness (Gmax) is a fundamental soil parameter, applicable to all types of geomaterials for static and dynamic loading. In-situ direct estimation of maximum stiffness or Gmax of soil are more accurate and reliable than the stiffness derived from resistance-based correlation or laboratory tests. This paper has provided a new method to estimate Ks based on Gmax. In order to validate the proposed method, results of the survey of loading tests and seismic geophysical tests of several sites were evaluated and compared. The results indicated that the proposed method in this study could be effectively used to predict the Ks of granular soils. This is much more accurate than the predictions of conventional methods.