Abstract: The suction-controlled triaxial shear tests were conducted on unsaturated weakly-expansive soil experiencing different suction histories over a wide range of suction. The maximum suction was applied by using the vapor equilibrium method for high suction and the axis translation technique at low suction. The results show that at the same net stress and suction, the stress-strain curves of the specimens subjected to drying-wetting cycle are situated at a higher level and a smaller contractive volumetric strain occurs during shearing, and the stress-strain curves of the specimens experiencing larger suction also raise up and a smaller contractive volumetric strain can be observed during shearing. Furthermore, the stress-strain and volumetric strain behaviors become more and more similar to the deformation characteristics of overconsolidated soil with the increase of the imposed maximum suction. The reason for the above phenomena is that the specimen experiences a larger suction as the specimen experiences a larger pre-consolidation pressure. Meanwhile, the shrinkage characteristics of weakly-expansive soil become significant due to water loss. After experiencing a larger suction, the void ratio decreases significantly, and thus the specimen exhibits the deformation characteristics similar to the overconsolidated clay during shearing. Therefore, in order to characterize the stress-strain relationship and the strength of unsaturated weakly-expansive soil, the specimen volumetric shrinkage caused by suction history should be considered.

Key words: unsaturated weakly expansive soil, suction history, vapor equilibrium method, volume shrinkage, overconsolidation