It is necessary to build a visco-elasto-plasitc constitutive model for unsaturated soils, because soils deform over time. Based on existed rate independent constitutive model, a rate dependent model which considers the influence of strain rate on soil behavior is developed. Previous test data indicated that the preconsolidate stress increased with the strain rate. Accordingly, the strain rate was included in the hardening equation,and thus the loading collapse yield surface was rate dependent. The one-dimensional constitutive equation of unsaturated soil was then obtained with the help of consistency condition. The model was used to compare with the existing test data. The model simulations show the model behaviors. The model was used to predicted experimental data for the degenerated cases included saturated condition and rate independent condition. Results show a good consistency.%非饱和土变形是随时间发展的,为了描述非饱和土随时间变化的长期变形行为,本文建立了非饱和土黏弹塑性模型.在已有的非饱和土率无关模型的基础上,考虑应变率对变形和强度影响,建立了一个非饱和土率相关的黏弹塑性模型.根据试验结果,应变率越大,屈服应力则越大,将屈服应力表示为应变率的函数,给出率相关影响的加载湿陷屈服面.利用一致性条件,给出了一维条件下非饱和土的增量方程.对模型进行数值分析,对模型基本行为进行预测.将模型退化饱和条件和率无关2种情形,利用已有的试验结果对模型进行了验证,结果表明模型可以用于预测非饱和土的蠕变行为.
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