压实膨胀土饱和抗剪强度的变动性

Variation of Saturated Shear Strength of Compacted Expansive Soil

饱和抗剪强度是工程设计的基本指标与描述非饱和抗剪强度的基准,然而其具有一定变动性,为探讨变动规律,在四联直剪仪上对6种制样压实度下的荆门弱膨胀土开展一维无荷载膨胀-固结-慢剪试验,将其结果与不同水化状态下的三轴试验数据对比.结果表明:相同应力状态下孔隙比状态的差别是造成该变动性的主因;先期应力历史与水化状态的差别导致相同应力状态下孔隙比状态的差异.水化状态为浸水膨胀稳定(膨胀势完全释放)后的饱和状态时,有效黏聚力随孔隙比增大规律性降低,有效内摩擦角对孔隙比并不敏感.水化状态为膨胀势未完全释放的饱和状态时,有效内摩擦角显著高于浸水膨胀稳定后的相应值,原因是膨胀势引发的剪胀效应造成的剪切抗力提高,反映于有效内摩擦角的增大.浸水膨胀稳定后有效内摩擦角是低且稳定的,相关工程应用及描述非饱和抗剪强度时,建议选取浸水膨胀稳定后的饱和抗剪强度参数作为相应指标.

Saturated shear strength is a key soil property and the reference of unsaturated shear strength,however,the variation of which is obvious. The mechanism of the variation of saturated strength was investigated. The direct shear tests under consolidated drained condition after the samples swelling to steady state were carried out for Jingmen expansive soil associated with six levels of compactness. The direct shear test results were compared with the results of triaxial compression tests. Comparative investigation finally discovered that the causation of the variation was the different void ratios under the same stress state,and the difference of void ratios was resulted from pre-stress history and hydration state. Under the hydration state of the swelling was complete,the effective cohesion decreases with the increasing void ratio regularly,the effective angle of internal friction was insensitive to void ratio which can be considered as a stable value. Under the hydration state of the swelling was restricted by the saturator（ void ratio is relatively lower） which is the conventional saturation method,the effective angle of internal friction is significantly higher than that of the previous hydration state. That was because the swell potential increases with the decreasing void ratio,a higher shear resistance can be mobilized by the dialtancy induced by higher swell potential. Since the effective angle of internal friction under the hydration state of the complete swelling is low and stable,it was suggested that the saturated strength parameters under that state should be adopted.