Characteristic Behavior of Cross-Anisotropic Deposits of Granular Soils

Triaxial compression tests were performed on sand to simulate the cross-anisotropic behavior of soil layers deposited by vertical gravitation. Specimens were created with horizontal and vertical bedding planes, which were obtained by air pluviation in the vertical direction into an upright mold and two halves of the horizontally lying mold respectively. After pluviation, horizontal specimens were water saturated and frozen, which allowed the assembly of the two halves to create a cylindrical specimen for testing. All specimens were isotropically confined at 20, 60, and 180 kPa. The characteristic behavior was controlled by the contact normals between the grains, which favor the vertical direction. Influence of the cross-anisotropy was analyzed by stress-strain, volume change, shear strength, and elastic properties. The behavior of the vertical specimens showed stiffer initial slopes, smaller strain-to-failure, higher shear strengths, less initial contraction and higher rates of dilation than the horizontal specimens. Cross-anisotropy was most pronounced for dense sand and reduces with increasing confining pressure and void ratio and vanishes at very high confining pressures and void ratios. The elastic properties evaluated from unloading-reloading cycles showed slightly higher values of Young's moduli for vertical specimens than for horizontal specimens and they increased with the sand density.