制样方法对非饱和土力学特性的影响

Effect of specimen preparation on mechanical behavior of unsaturated soils

以一种非膨胀性黏土为试验材料,对孔隙比相近的非饱和压实试样和预固结试样进行一系列等吸力控制下的等向压缩试验和三轴剪切试验,研究了制样方法对非饱和土的压缩特性和剪切特性的影响。由等吸力等向压缩试验结果表明:初始孔隙比相近的预固结样和压实样在等向净应力20 k Pa条件下进行等吸力平衡,平衡过程中预固结试样的孔隙比明显减小而压实样的变化不大;其原因是两种试样的初始吸力和土结构存在差异。此外,预固结样和压实样在吸力150 k Pa条件下,预固结样的含水率随着等向净应力的增大而减小,而压实样的含水率几乎不变。上述变形特性可用SFG弹塑性模型说明。在净围压和吸力相同条件下对剪切前孔隙比相同的两种试样进行了三轴剪切试验,试验结果表明:在剪切前的密度、剪切时的吸力和净围压相同条件下,预固结样的偏应力–应变曲线和强度明显高于压实试样的曲线和强度。其原因可用两种试样的孔隙尺寸分布不同来解释。

The soil used in this study is one of non-expansive clays. A series of suction-controlled isotropic compression tests and suction-controlled triaxial compression tests are designed with the main objective of investigating the compression and shear behavior of unsaturated soil samples made via either compaction or pre-consolidation method. The isotropic compression test results indicate that the void ratio of pre-consolidation specimen decreases with the increasing suction value under isotropic net stress of 20 kPa, while the void ratio of compacted specimen shows little change during the suction equilibrium process. The reason is that different initial suctions and soil structures exist in two types of specimens. In addition, the pre-consolidated specimen has obvious drainage occurring during imposing suction t^om the initial suction to 150 kPa under isotropic net stress of 20 kPa, while the compacted specimen shows a little change. These deformation characteristics can be explained by SFG elastoplastic model for unsaturated soils. The triaxial compression test results indicate that the deviatoric stress-strain curve and strength of pre-consolidation specimen are higher than those of compacted specimen under the same suction and net confining pressure during triaxial shearing and almost the same density before the shearing. The reason is the difference in the pore-size distributions of the two kinds of specimens.