Stiffness of sands through a laboratory test database. Geotechnique

Abstract

Deformations of sandy soils around geotechnical structures generally involve strains in the range small (0 . 01%) to medium (0 . 5%). In this strain range the soil exhibits non-linear stress-strain behaviour, which should be incorporated in any deformation analysis. In order to capture the possible variability in the non-linear behaviour of various sands, a database was constructed including the secant shear modulus degradation curves of 454 tests from the literature. By obtaining a unique S-shaped curve of shear modulus degradation, a modified hyperbolic relationship was fitted. The three curve-fitting parameters are: an elastic threshold strain ª e , up to which the elastic shear modulus is effectively constant at G 0 ; a reference strain ª r , defined as the shear strain at which the secant modulus has reduced to 0 . 5G 0 ; and a curvature parameter a, which controls the rate of modulus reduction. The two characteristic strains ª e and ª r were found to vary with sand type (i.e. uniformity coefficient), soil state (i.e. void ratio, relative density) and mean effective stress. The new empirical expression for shear modulus reduction G/G 0 is shown to make predictions that are accurate within a factor of 1 . 13 for one standard deviation of random error, as determined from 3860 data points. The initial elastic shear modulus, G 0 , should always be measured if possible, but a new empirical relation is shown to provide estimates within a factor of 1 . 6 for one standard deviation of random error, as determined from 379 tests. The new expressions for non-linear deformation are easy to apply in practice, and should be useful in the analysis of geotechnical structures under static loading