高吸力下黏性土的抗剪强度和体变特性

Shear strength and volume change behavior of clay-rich soil at high suctions

非饱和土中土-水之间的相互作用可区分为毛细作用和吸附作用,已有的非饱和土力学特性的研究大都局限于较低吸力、毛细作用占优范围。实践中由于环境的变化,地表土体常经历干湿循环及处在低含水率、高吸力状态,此时吸附作用占优。针对高岭土-河砂配制的非膨胀性黏性土,采用饱和盐溶液蒸汽平衡法,从脱湿和吸湿两种吸力路径下对土体施加高吸力。测试了高吸力下土体的强度和变形特性,试验中选用了0(接近无侧限)、25、50、100 kPa共4组小围压。试验结果表明,高吸力下土体表现为应变软化型破坏和剪胀性。随着围压的施加,土体从沿纵向开裂的张裂破坏过渡为剪切破坏。验证了修正后的Bishop非饱和土强度公式不适用于描述高吸力时峰值抗剪强度的变化,得到了高吸力下峰值抗剪强度可用相对于净应力的临界状态强度和剪胀作用来表示。分析发现,高吸力时土体的抗剪强度和比表面积直接相关,吸力对土体抗剪强度的作用取决于土体集聚体组构的形成和发展程度及其导致的剪胀作用。

The soil water interaction in unsaturated soils can be divided into capillarity and adsorption. The current study of unsaturated soils is mostly limited to lower suction range where capillarity dominates. In practice, due to climatic changes, soils near the ground surface often experience cyclic wetting and drying, and the low water content and high suction conditions, where adsorption dominates. Using the vapor equilibrium technique on the saturated salt solution, the high suctions are controlled for non-expansive kaolin-sand soil under drying and wetting paths respectively. The strength and deformation behaviors under high suction are tested under four confining pressures of 0 （close to unconfined）, 25, 50, 100 kPa. The results show that the soils under high suctions indicate strain softening failure and dilatancy. With confining pressure applied, the failure mode change from the longitudinal cracking to shear failure. It is proved that the modified Bishop＇s effective stress model is not suitable for describing the peak shear strength at high suction. The peak shear strength can be expressed by the net stress-dilatancy relationship. The peak shear strengths are directly related to specific surface area and depend on the development of aggregates and dilatation.