Anisotropic small-strain stiffness of calcareous sand affected by sample preparation, particle characteristic and gradation

Sands exhibit a directional diversity in shear modulus at small strains, reflecting the anisotropic stiffness behaviour in the structure. In this paper, sample preparation method, particle shape and particle size are considered as parameters to produce samples with various initial fabric. Five preparation methods, namely, air and water pluviation, dry and moist tamping and dry funnel deposition are used to reconstitute the samples. The stiffness anisotropy of calcareous sand and Mol silica sand is quantified by the small-strain modulus G₀ measured in horizontal and vertical planes with the bender element technique in triaxial tests. Test results show that calcareous sands behave as an elastic homogeneous continuum material at small strains. Calcareous samples prepared by the air pluviation method possess the highest anisotropic ratios. The lowest stiffness anisotropy exists in the samples prepared by moist tamping and dry funnel deposition methods. Compared with the anisotropic ratios of the air pluviation samples from the literature, the notably higher values for the calcareous sand in this study are attributed to the lower sphericity. In addition, less prominent stiffness anisotropy is found in calcareous sands with smaller particle sizes (D₅₀).