Voids and Granulometry: Effects on Shear Modulus of Unsaturated Sands

This paper describes the results of an experimental investigation of capillary effects on the low strain shear modulus of sands in a partially saturated condition. It studies: (1) Void ratio; (2) confining pressure; (3) grain shape; and (4) grain size distribution on shear modulus. The results of resonant column tests show that capillary stresses significantly increase the shear modulus of partially saturated sands. These effects are more pronounced for soils with low void ratios and confining pressures. The optimum degree of saturation increases with increasing void ratio and a linear relationship exists between the maximum shear modulus ratio and void ratio. The slope of this relationship is not affected by confining pressure and grain size distribution, and instead depends on the soil grain shape. If the smallest grains of a sand are larger than the 400 sieve size, the grain size distribution does not affect the optimum degree of saturation, but only affects the maximum shear modulus in a partially saturated condition. The content of the minus 400 sieve size fraction can affect both the maximum shear modulus and the optimum degree of saturation for unsaturated sands. Soil grain shape also affects both the maximum shear modulus and the optimum degree of saturation.