吸力历史对非饱和土力学性质的影响

Effect of suction history on mechanical behavior of unsaturated soils

现在被广泛公认的由Fredlund提出的非饱和土力学的双参数理论,即净应力和吸力为非饱和土的应力状态变量,不能直接考虑吸力历史及其饱和度对非饱和土的应力-应变关系和强度的影响。非饱和土三轴试验结果表明,即使净应力和吸力相同的条件下,经过干-湿循环试样与未经过干-湿循环试样的应力比-应变关系和强度是不相同的。在其他条件相同时,经历过干-湿循环的试样比未经过干-湿循环试样的应力比-应变关系要高、强度大和体变小。经过干-湿循环试样的饱和度低而强度高,主要是由于经过先期较高的吸力,相当于受过较大的前期有效压力,使试样成为超固结土。更多不同吸力历史的对比试验有待于进一步研究,以便为非饱和土的水力-力学特性耦合弹塑性本构模型定量地表示上述非饱和土的性质提供基础性试验数据。

A widely accepted two parameters theory of unsaturated soil mechanics by Fredlund, using net stress and suction as stress-state variables, cannot consider the effect of suction history and saturation on stress-strain behaviour and strength of unsaturated soils. In this paper,the triaxial compression test results show that even if the same path of net stress and suction, stress-strain behaviour and strength are not the same between the samples experienced different suction history. While other conditions are the same, the samples experienced drying-wetting cycle have higher relationship of stress ratio-strain, higher strength, smaller volumetric deformation than the sample not experienced drying-wetting cycle. The samples experienced drying-wetting cycle have low saturation but high relationship of stress ratio-strain and strength. It is because larger suction experienced previously is equivalent to larger effective pressure experienced, that makes the sample to become overconsolidated state. Study of effect of different suction histories on unsaturated soil behaviour is needed further for providing the basis of experimental data. With the data, the elastoplastic constitutive model coupling hydraulic and mechanical behaviour could express behaviour of unsaturated soils more accurately and quantitatively.