An endochronic strain rate-sensitive model for soils susceptible to dilatancy

The object of this research was to apply the concepts of endochronic plasticity toward developing, from thermodynamic principles, a strain rate-sensitive constitutive equation for soils with dilatant capability. The approach was to set the theory in a three dimensional framework and endow the resulting constitutive relations with the capability for accounting for strain rate-sensitivity and dilatancy.; A pair of constitutive equations, which are derived from deformation kinetics, and are based on the concepts of critical state theory, is proposed to describe the rate-dependent deviatoric and hydrostatic responses of soil.; The degree of time-dependency of soil behavior differs depending on the soil type, each type of soil having its own intrinsic time-dependent characteristics.; For the study of their creep characteristics, sands have some convenient properties. First, sands are very permeable and, therefore, the creep characteristics of sands can be directly observed by chained creep tests without any influence upon the mean effective principal stresses caused by the variation of pore water pressure. Similarly, it is easy to maintain a constant mean effective principal stress throughout the drained creep test. Another convenient characteristic of sand is that it is cohesionless; that there are no physico-chemical bonding forces between sand particles as long as they are saturated or completely dry. Due to the above advantages, and disregarding its shortcomings of having inconspicuous time dependency, Ottawa sand was chosen as the material for this study of the strain rate-sensitive constitutive equations. It is shown that the theory yields analytical results which are in close agreement with the experimental results.; Of consequence is the fact that the strain rate-sensitive constitutive equation applies to three-dimensional stress based on strain history and is thus not limited to those associated with creep. In this study, the simplest loading condition-creep test was employed to find the material parameters in the constitutive equation. After the finding of the material parameters, the strain rate-sensitive constitutive equation may be used for predicting the material response to any three dimensional loading. (Abstract shortened with permission of author.)...