The parameters obtained from oedometric consolidation tests are commonly used in the development of constitutive modeling and for engineering practice. This paper focuses on the influence of the natural deposition plane orientation on oedometric consolidation behavior of three natural clays from the southeast coast of China. Oedometer tests were conducted on intact specimens prepared by sampling at a series of angles relative to the natural deposition plane. For each specimen, yield stress,compressibility indexes, secondary compression, and permeability coefficients were determined. The influence of the sampling angle on these properties was investigated, revealing that yield stress, compression index, swelling index, creep index, ratio of secondary compression coefficient to compression index(Cae/Cc) and permeability coefficient were all dependent to some extent on the sampling angle. These findings indicate the role of the anisotropy due to the natural deposition on the oedometric consolidation behavior.
This work focuses on the uniqueness of rate-dependency, creep and stress relaxation behaviors for soft clays under one-dimensional condition. An elasto-viscoplastic model is briefly introduced based on the rate-dependency of preconsolidation pressure. By comparing the rate-dependency formulation with the creep based formulation, the relationship between rate-dependency and creep behaviors is firstly described. The rate-dependency based formulation is then extended to derive an analytical solution for the stress relaxation behavior with defining a stress relaxation coefficient. Based on this, the relationship between the rate-dependency coefficient and the stress relaxation coefficient is derived. Therefore, the uniqueness between behaviors of rate-dependency, creep and stress relaxation with their key parameters is obtained. The uniqueness is finally validated by comparing the simulated rate-dependency of preconsolidation pressure, the estimated values of secondary compression coefficient and simulations of stress relaxation tests with test results on both reconstituted Illite and Berthierville clay.
In this study, we aim to investigate a unified modeling method for the monotonic and cyclic behaviors of sand and clay. A simple double-yield-surface model, with plastic hardening modulus and dilatancy relation being dependent on density state unlike in existing approaches, is developed by considering the location of the critical state line. The model is used to simulate the drained and undrained tests of various sands and clays under monotonic and cyclic loadings. Prediction results are compared with experimental results, which show that the proposed approach is capable of modeling the monotonic and cyclic behaviors of sand and clay.
Experiments show that silts and silty soils exhibit contraction followed by dilation during shearing and the slope of failure line decreases at large strains, termed as phase transformation behaviour. This paper is to develop a new micromechanical stress-strain model that accounts for the phase transformation behaviour by explicitly employing the phase transformation line and its related friction angles. The overall strain includes plastic sliding and plastic compression among grains. The internal-friction angle at the phase transformation state and the void state variable are employed to describe the phase transformation behaviour. The model is examined by simulating undrained and drained triaxial compression tests performed on Pitea silts. The local stress-strain behaviour for contact planes is also investigated.
