Overall understanding of the factors for inelastic behaviour of geomaterial and their interactions

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Factors, viscosity, inviscid cyclic loading effect and ageing, which affect the stress-strain behaviour of geomaterial (i.e., clays, sands, gravels, cement-mixed soils, geosynthetic reinforcement, EPS etc.) as well as interactions of these factors with elasto-plastic properties were investigated by performing a great amount of drained plane strain and triaxial compression tests and direct shear tests. A general constitutive model that can simulate the above and can be used in numerical analysis of geotechnical boundary-value problems was developed. The major findings include the followings. Firstly, the geomaterial exhibits different viscosity types depending on particle shape and grading, categorized as 1) Isotach, 2) Combined, 3) TESRA and 4) Positive and Negative (P&N). Isotach is characterized by an increase in the strength with strain rate, while TESRA by the same strength in monotonic loading at different but constant strain rates and P&N by a decrease in the strength with an increase in the strain rate. These viscosity types have a positive component in that the stress increases upon a sudden increase in the strain rate and the strain increases during sustained 1