Estimating the shear modulus of gravelly soils

A special large-scale torsional resonant column apparatus was used to test gravelly soils. Values of small strain elastic shear modulus (Gm,) and modulus reduction relationships [shear modulus (G) versus shear strain ( gamma)] were measured for specimens of uniform and graded crushed limestone gravel, graded river gravel, standard Ottawa and crushed limestone sands, and gravel-sand-silt mixtures. Measurements of G(max) were used to modify existing three-dimensional constitutive equations for soil elasticity for application to gravelly soils. The value of G(max) for relatively clean uniform and graded gravels was found to increase with particle size. Soils with a variety of gradations were tested to identify the particular particle size in a graded material that is effective in determining G(max) With respect to modulus reduction, the need to normalize both modulus and strain is demonstrated. Normalization of both modulus and strain (GIG,a, versus gamma/gamma(r), where gamma(r) is defined as reference strain) leads to relationships that are approximately independent of stress level for a given material.