非饱和土的修正SFG模型研究

Modified SFG model for unsaturated soils

从非饱和土的有效应力出发,对SFG模型进行了修正,将饱和度的影响引入到了模型当中,使得模型在不增加参数的同时可以反映更多的实验现象。首先简单介绍了SFG模型。然后以功的表达式推导得到的非饱和土有效应力为基础给出了非饱和土的体变方程,在饱和阶段该方程可以自动退化为饱和土的体变方程。结合土水特征曲线方程,推导得到了修正模型的加载湿陷屈服面方程,由此得到的屈服面方程不仅是吸力的函数,同时也是饱和度的函数。屈服面可以连续光滑地从饱和状态过渡到非饱和状态,并可以预测干燥时出现塑性变形的现象。此外它还可以反映SFG模型无法反映的现象,即考虑饱和度的影响,对于吸力相同饱和度不同的土样,给出的屈服应力将不同。最后利用已有试验数据对修正模型进行了验证,说明了修正模型与试验结果是相符的。

A modified SFG model is developed based on the principle of effective stress. With the effective stress of unsaturated soils deduced from the expression of input work, the degree of saturation is naturally introduced into the proposed model without any additional parameters. After a simple introduction to the SFG model, the volume-change behaviors and the soil-water characteristics are discussed, and then the loading collapse curve is formulated. The loading collapse yield equation in the modified model is a function not only of suction, but also of the current degree of saturation. The yield surface provides a smooth transition between saturated and unsaturated states, which is convenient for simulating the plastic deformation during drying process. The simulated results of the modified model are compared with the experimental data available in literatures, showing that the modified model agrees well with the experimental results. Compared with the original SFG model, the new model yields better results at different degrees of saturation.