Small-Strain Characteristics of Reconstituted Soils: The Effect of Slurry Water Content and Fabric Anisotropy

Determination of small-strain properties of soils is essential for many geotechnical applications. Reconstituted specimens have conveniently been used to characterize small-strain properties of cohesive soils in the laboratory. In this study, the influence of slurry water content (W-s) and fabric anisotropy on the small-strain properties of reconstituted kaolinite and illite specimens was investigated. Bender elements were employed, within triaxial testing equipment, to obtain vertically propagated, horizontally polarized, shear wave velocity measurements and corresponding shear moduli during the consolidation stage of undrained triaxial compression tests. The soils were initially prepared at water content values of one and one-half (1.5x) and three (3x) times the respective liquid limit for each soil type. The shear wave velocity and shear modulus data were normalized to the void index by following a procedure that was similar to procedures that have previously been used to normalize compression and undrained shear strength data. Unique "intrinsic" relationships for shear wave velocity or shear modulus, independent of soil fabric, were not observed during this study. Inherent fabric anisotropy was also assessed by comparing the aforementioned triaxial shear wave velocity data to measurements of horizontally propagated, vertically polarized, shear wave velocity that were obtained by utilizing bender elements within a consolidation device. The amount of fabric anisotropy was dissimilar and the characteristics of the cross-anisotropic fabric were not observed for the specimens. The amount of inherent fabric anisotropy (V-s,V- HV/V-s,V- VH) ranged from 0.63 to 0.97 for the kaolinite and illite specimens with w s values of 1.5x the liquid limit and ranged from 1.13 to 1.21 for kaolinite specimens with w s values of 3x the liquid limit. During the shearing stage, inconsistent and unreliable relationships were obtained for the shear wave velocity-vertical effective stress behavior and shear modulus-axial strain behavior. As discussed herein, the w s level should be considered when reconstituting soil specimens for small-strain stiffness determination.