侧限条件下增湿时湿陷性黄土的变形及持水特性

用改装的非饱和土直剪仪在无应力及净竖向应力作用下对湿陷性黄土进行分级增湿试验,测量增湿过程中变形及吸力的变化,分析增湿前孔隙比(无应力时)及净竖向应力对增湿时湿陷性黄土的变形及持水特性的影响,探讨无应力与净竖向应力作用时增湿持水特性之间的关系,提出力水耦合作用下孔隙比与吸力关系的表达式及以饱和度与吸力关系表征的持水特性模型。研究结果表明:力水耦合作用下,孔隙比与归一化吸力关系可用对数函数来描述,可以用孔隙比的变化来反映净竖向应力对持水特性的影响。无应力及净竖向应力作用时,只要孔隙比相同,则饱和度与吸力间关系相同。吸力小于阈值时,增湿前孔隙比和力水耦合作用所致孔隙比的变化对含水率与吸力间关系皆有较大影响;大于阈值时,几乎没有影响,且可用同一幂函数描述,据此提出考虑孔隙比变化的修正V-G模型,该模型可以预测无应力及净竖向应力作用时湿陷性黄土的增湿持水特性,预测结果与试验结果吻合较好。

Deformation and water retention behaviour of collapsible loess during wetting under lateral confinement

Stepped wetting tests were performed on collapsible loess under null stress and net vertical stress by using refitted direct shear apparatus for unsaturated soils. The variation of deformation and suction were measured during wetting. The influences of void ratio at the beginning of wetting(null stress) and net vertical stress on deformation and water retention behaviour of collapsible loess were analyzed during wetting. The wetting water retention behaviour under null stress was compared with that under net vertical stress. The models describing the relation of void ratio versus the suction and the water retention behaviour on the degree of saturation versus the suction were proposed under hydro-mechanical coupling. Having considered hydro-mechanical coupling，the relationship of void ratio and normalized suction was described by a logarithmic function and the influence of net vertical stresses on the water retention behaviour was reflected by the variation of void ratio. The relationship of the suction and degree of saturation under hydro-mechanical coupling was the same as that under null stress for the same void ratio. When the suction was less than a certain threshold value，the variations of the void ratio either at the beginning of wetting or induced by hydro-mechanical coupling had great influence on the relationship of suction and water content. A modified V-G model considering the variations of the void ratio was put forward. The model described the wetting water retention behaviour under null stress and net vertical stresses. The predicted results were in good agreement with the test results.