Wetting water retention behaviors of intact loess under isotropic compression stress

The wetting tests by stages on intact loess with natural state are performed under different isotropic compression stresses by using the refitted triaxial equipment for shearing and permeability measurement of unsaturated soil. The influences of stresses on wetting water retention curves are analyzed. The models describing the water retention behaviour expressed by the degree of saturation and water content versus the suction are proposed, in which the effects of isotropic compression stress are directly considered. The results show that the stress has remarkable influence on degree of saturation as a function of suction. Its effect on the relationship between water content and suction depends on the magnitude of suction. When the suction is higher than a certain threshold value, the effect is much less pronounced, and the data appear to lie on a curve. When it is lower than the threshold value, the effect is obvious. The air-occlusion suction increases and the saturated water content decreases with the increasing stress, and the relations between them can be described by linear and logarithm functions respectively. There are all unique relationships of both degree of saturation and water content ratio (defined as water content to saturated water content ratio) versus suction ratio (defined as suction to air-occlusion suction ratio) under different stresses. Moreover, these can be descried by the proposed models. Compared with the water retention models taking void ratio at applied stress as variable, the models taking isotropic compression stress as variable are more convenient for engineering application. The predicted results of both liquid saturation and water content against functions of suction are in good agreement with the test results.