Effects of time and rate on the stress-strain-strength behavior of soils

抄録

This paper presents main data from both oedometer tests and triaxial tests on Hong Kong Marine Clay (HKMC) and a mixture of bentonite-silica. The oedometer tests include (i) multi-staged loading tests with unloading/reloading and enough time for creep and swelling in 1D straining and (ii) step-changed constant rate of strain compression tests with unloading/reloading in 1D straining as well. The triaxial tests include K_o-consolidated undrained compression or extension tests with constant (or stepped changed) strain rates. This paper will discuss the time effects and rate effects with a special attention to the non-linear and elastic visco-plastic behavior. Based on the test data presented above, this paper presents a brief review of the works of elastic visco-plastic (EVP) modelling of the time-dependent stress-strain behaviour of soils in one-dimensional straining (1D) and in 3D stress state. A few important concepts and their physical meanings are explained. The 1D EVP model is briefly reviewed with a comparison with the classic Maxwell’s rheological model. It is found that Yin and Graham’s 1D EVP model is an extension of Maxwell’s rheological model for considering the nonlinear behaviour of soils. The recent extension of the EVP modelling framework to consider the swelling of a saturated soil is introduced. A 3D EVP model is also introduced and discussed. A nonlinear creep function proposed by the author is presented. This function has been used in refined 1D and 3D EVP models. It is concluded that the time and rate effects of clayey soils shall be considered in a suitable constitutive model.