Abstract:
Two series of triaxial compression tests were performed on vertical and horizontal specimens of sand to simulate the cross-anisotropic behavior of soil layers deposited by vertical gravitation in the field. Specimens with horizontal and with vertical bedding planes were created in cylindrical molds and tested in conventional triaxial compression tests. The specimens were pluviated in the vertical direction into an upright mold to create vertical specimens and into the two halves of the mold lying horizontally to create horizontal specimens. The latter were water saturated and frozen and the two halves were assembled to create a cylindrical specimen for testing. These specimens were isotropically confined at 20, 60, and 180 kPa and tested to reveal the behavior of the cross-anisotropic deposit. The characteristic behavior was controlled by the contact normals between the grains which favor the vertical direction, and the stress-strain, volume change, shear strength and elastic properties were analyzed to determine the influence of cross-anisotropy. The behavior of the vertical specimens showed stiffer initial slopes, smaller strain-to-failure, higher shear strengths and friction angles, less initial contraction and higher rates of dilation than the horizontal specimens. Cross-anisotropy was most pronounced for dense sand and it reduces with increasing confining pressure and increasing void ratio and vanishes at very high confining pressures and high 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.
