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 (G_max) and modulus reduction relationships [shear modulus (G) versus shear strain (γ)] 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 (G/G_max versus γ/γ_r, where γ _r, is defined as reference strain) leads to relationships that are approximately independent of stress level for a given material.