Bentonite-based materials are candidate buffer materials for the geological disposal of radioactive waste in many countries. Once the disposal facility is closed and the groundwater level recovers, the buffer will gradually become saturated by the infiltration of groundwater. The swelling properties of saturated bentonite affect the distribution of dry density and the stress state within the buffer. Therefore, to evaluate the long-term safety of the buffer, a model must be developed that can continuously express the mechanical behavior of bentonite from the construction and operation of the repository for disposal (the unsaturated state) to the resaturation phase (saturated state). In this study, the existing elastoplastic constitutive model for saturated expansive soils was extended to predict the mechanical response in the unsaturated state. In formulating this model, the effective degree of saturation and the plastic volumetric strain were employed as the hardening parameters to express the changes in stiffness and swelling properties due to desaturation or saturation. In addition, a method was proposed for estimating the material parameters added to the expanded constitutive model. This study demonstrated the validity of the proposed constitutive model and the parameter estimation method by comparing the results of simulations with those of laboratory tests.

膨润土基材料是许多国家放射性废物地质处置的候选缓冲材料。一旦处置设施关闭，地下水位恢复，缓冲区将因地下水的入渗而逐渐饱和。饱和膨润土的膨胀特性影响干密度分布和缓冲层内的应力状态。因此，为了评估缓冲器的长期安全性，必须开发一个模型，能够连续表达膨润土从处置库的建设和运营（非饱和状态）到再饱和阶段（饱和状态）的力学行为。 . 在这项研究中，将现有的饱和膨胀土弹塑性本构模型扩展到预测非饱和状态下的力学响应。在制定该模型时，采用有效饱和度和塑性体积应变作为硬化参数，以表达由于去饱和或饱和引起的刚度和膨胀特性的变化。此外，还提出了一种估计添加到扩展本构模型中的材料参数的方法。本研究通过将模拟结果与实验室测试结果进行比较，证明了所提出的本构模型和参数估计方法的有效性。提出了一种估计添加到扩展本构模型中的材料参数的方法。本研究通过将模拟结果与实验室测试结果进行比较，证明了所提出的本构模型和参数估计方法的有效性。提出了一种估计添加到扩展本构模型中的材料参数的方法。本研究通过将模拟结果与实验室测试结果进行比较，证明了所提出的本构模型和参数估计方法的有效性。