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This paper targets the expansive soils in Heilongjiang and Ankang to explore the influence of initial dry density, dry-wet cycle, and freeze-thaw cycle on the soil-water characteristics. The centrifuge method was used to obtain the soil-water characteristic curves (SWCCs) with different conditions. The volumetric strain of SWCC was modified based on the shrinkage test, and the corresponding fitting equations considering different factors were established. The results show that the volumetric water content is modified to consider the volume shrinkage effect of expansive soil, and the modification is more obvious in the high matric suction range. The smaller the initial dry density is, the worse the water-holding capacity of the sample is, and the smaller the air intake value is. The greater the time of the dry-wet cycle is, the greater the saturated volumetric water content of the sample is, and the corresponding water-holding capacity is significantly reduced. When the dry-wet cycle increases to a certain extent, the structure becomes stable. With the increase of the freeze-thaw cycle, the saturated volumetric water content first decreases and then increases. Similarly, after several times of the freeze-thaw cycle, the structure is basically stable. The fitted Gardner model equations under different conditions were proved to be able to describe the SWCCs of the two targeted expansive soils.

In order to reveal the mechanical characteristics of the unsaturated undisturbed Ili loess in westerly region, the isotropic compression tests controlling suction, the triaxial shrinkage tests controlling net mean stress and consolidation shear tests controlling net confining pressure and suction were carried out under different soluble salt contents. The objective of investigation is to explore the normalized characteristics of compression curve, soil water characteristic curve and critical state line. The results show that the ratio of void ratio to initial void ratio and the ratio of net mean stress to yield net mean stress are suitable to normalize the compression curves under different suctions in the isotropic compression test. The soil water characteristic curves under different net mean stresses in the triaxial shrinkage test can be normalized by the ratio of water content to saturated water content and the ratio of suction to air entry value. In the consolidation shear test controlling constant suction, the unsaturated critical state lines under different suctions can be normalized by the corresponding saturated critical state line in the plane of effective net mean stress and deviator stress. The unsaturated critical state lines under different suctions in the plane of void ratio and net mean stress can be normalized by means of degree of gas saturation and the ratio of unsaturated void ratio to saturated void ratio under the same effective net mean stress. The results provide potential benefits for the constructions of large-scale water conservancy projects in the special area of Central Asia.

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