Mechanical Properties of Artificial Structured Soils Under a Conventional Drained Loading–Unloading–Reloading Stress Path

Triaxial tests were performed on artificially structured soils, including initially isotropic and initially stress-induced anisotropic soils, and remolded samples under consolidation drained conditions at confining pressures of 50, 100, 200 and 400 kPa to investigate their volumetric contraction behaviors upon axial unloading. The values of axial strain at which unloading begins are set as 3, 6, 9 and 12% to apply the axial unloading–reloading stress path. Factors, including confining pressure, axial strain at which unloading starts, structure and anisotropy, are investigated to analyze their influences on the behaviors of volumetric contraction due to axial unloading. The results demonstrate that: (1) for the three types of tested samples, including initially isotropic, initially stress-induced anisotropic and remolded samples, the volumetric strains are contractive during the process of axial unloading in unloading–reloading stress cycles under all of the confining pressures; (2) the higher the confining pressure and axial strain at which axial unloading starts, the greater the volumetric contraction due to axial unloading is; (3) in comparison with initially isotropic structured soils, initially stress-induced anisotropic samples have smaller volumetric contraction because of axial unloading at low confining pressure; and (4) stress-induced anisotropy can increase volumetric contraction due to axial unloading, but it has very weak influences on artificially structured soils at low confining pressure.