等向压缩应力条件下原状黄土的吸湿持水特性

用改装的非饱和土三轴剪切渗透仪,在不同等向压缩应力作用下对天然状态的原状黄土进行了分级浸水试验,分析了应力对吸湿持水曲线的影响,提出了可以直接考虑等向压缩应力影响,以饱和度及含水率与吸力关系表征的持水特性模型。研究结果表明:应力对饱和度与吸力关系的影响较大;对含水率与吸力间关系的影响与吸力大小有关,当吸力大于阈值时几乎没有影响,可近似归一,当吸力小于阈值时影响较大。随着应力增大,脱气吸力值增大,饱和含水率减小,且可分别用线性函数及对数函数描述之。不同应力下,饱和度及含水率比(含水率与饱和含水率之比)与吸力比(吸力与脱气吸力值之比)关系皆可以归一,且可用提出的模型描述。该模型直接把等向压缩应力作为变量,与以应力作用下孔隙比作为变量的持水曲线模型相比,更便于实际工程应用。模型对饱和度及含水率与吸力关系的预测结果与试验结果吻合较好。

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.