关键词: 黏滞性, 弹黏塑性, 过应力理论, 临界状态, 本构模型

Abstract: 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.

Key words: viscosity, elasto-viscoplasticity, overstress theory, critical state, constitutive model