临界状态是土的重要破坏特征，是当今许多土本构模型建立的基础。由于工程和试验中不能忽略时间因素，临界状态实际上是土在一定的时间作用下或者说一定的加载速率作用下表现出的破坏规律。率相关本构模型作为考虑了时间对土应力-应变关系影响的本构模型，理应可以描述临界状态。通过使用较为常用的率相关本构模型——过应力弹黏塑性模型对三轴不排水和排水剪切进行预测，探讨了这些模型对临界状态的描述情况。预测结果表明：（1）第1类过应力弹黏塑性模型（该模型认为屈服面是黏塑性体积应变率的等值面）计算所得的三轴不排水应力路径在临界状态线的下方出现应变软化，并且应力路径趋向于坐标原点，不能终止于临界状态；（2）第2类过应力弹黏塑性模型（认为屈服面是黏塑性标量因子的等值面）在对高应变率三轴排水剪切进行预测时，所得的最终应力比超过临界状态应力比；（3）第3类过应力弹黏塑性模型，亦即时间UH模型（认为屈服面是统一硬化参量变化率的等值面，并认为土产生应力塑性变形）在三轴不排水和排水剪切条件下均能较好反映临界状态。通过3种模型的公式分析了前述预测结果产生的原因。

The critical state, as an important failure characteristic of clays, is the basis of most existing constitutive models. Since the temporal effect cannot be neglected in laboratory tests, the critical state observed in tests is actually a failure phenomenon occurring in clays under the influence of time or a loading rate. Rate-dependent constitutive models, which consider the influence of time on the stress-strain relation of clays, should be able to describe the critical state. In order to characterize the critical state for rate-dependent constitutive models, the overstress elasto-viscoplastic (EVP) constitutive models are used to simulate the triaxial undrained and drained compression tests. The simulated results show that: 1) The triaxial undrained stress paths predicted by the first kind of overstress EVP models (which consider the yield surface to be a locus of constant viscoplastic volumetric strain rate) show strain softening below the critical state line, and they approach the origin of the coordinate system, but cannot attain the critical state. 2) In predicting the triaxial drained compression test at a high strain rate, the final stress ratio calculated by the second kind of overstress EVP models (which consider the yield surface to be a locus of constant viscoplastic scalar factor) exceeds the critical-sate stress ratio. 3) The third kind of overstress EVP model, i.e. the time-dependent UH model (which takes the stress-induced plastic deformations into account, and considers the yield surface to be a locus of the constant rate of unified hardening variable) can describe the critical state well in simulating both the triaxial undrained and drained compression tests.