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.
Volumetric contraction due to axial unloading Artificially structured soils Anisotropy Axial unloading–reloading stress path Triaxial compression
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The authors appreciate the financial support from the CAS Pioneer Hundred Talents Program (Liu Enlong) and the National Natural Science Foundation of China (NSFC) (Grant Nos. 51009103 and 51579167).
The financial support is from the National Natural Science Foundations of China (NSFC). This study is also funded by Open Fund Research at the State Key Laboratory of Hydraulics and Mountain River Engineering (No. SKHL1508).
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