Effect of specimen preparation on mechanical behavior of unsaturated soils

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 from 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.