吸力历史对非饱和弱膨胀土力学性质的影响

对经历较广吸力范围内不同吸力历史的非饱和弱膨胀土进行了一系列吸力控制的三轴剪切试验。关于最大吸力的施加，高吸力采用蒸汽平衡法；较低吸力采用轴平移技术。试验结果表明：在净应力和吸力相同条件下，经过湿化试样的应力-应变关系曲线升高、剪缩体变小；经过高吸力试样的应力-应变关系曲线也升高、剪缩体变小，随着经历过最大吸力的增加其应力比-应变关系、体变表现出的超固结土特性明显。其主要原因是前期试样受过较大的吸力，相当于受过较大前期固结压力，同时弱膨胀土失水收缩性明显，经过较大吸力后试样孔隙比明显减小，使试样剪切过程中表现出超固结黏土的特性。因此，讨论非饱和弱膨胀性土的应力-应变关系和强度时需考虑吸力历史引起的体积收缩影响。

Effect of suction history on mechanical behavior of unsaturated weakly-expansive soils

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.