Various viscosity types of geomaterials in shear and their mathematical expression
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Author list: Tatsuoka F., Dibenedetto H., Enomoto T., Kawabe S., Kongkitkul W.
Publisher: Elsevier
Publication year: 2008
Journal: Soils and Foundations (0038-0806)
Volume number: 48
Issue number: 1
Start page: 41
End page: 60
Number of pages: 20
ISSN: 0038-0806
eISSN: 2524-1788
Languages: English-Great Britain (EN-GB)
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Abstract
The viscous properties, or loading-rate effects on the stress-strain behaviour, of unbound and bound soils, in particular unbound granular materials, are summarised. The viscous properties were evaluated by stepwise changing the strain rate, ε̇, and performing sustained loading during otherwise monotonic loading (ML) at a constant ε̇ and also by performing ML tests at different constant values of ε̇. Four basic viscosity types, Isotach, Combined, TESRA (or Vis-cous Evanescent) and Positive & Negative (P & N), which were recently found are described. The Isotach type is the most classical one and, in the case of ML, the current viscous stress component is a function of instantaneous irreversible strain, εir and its rate, ε̇ir. So, the strength during ML at a constant ε̇ increases with ε̇. With the other three types, the viscous stress increment that has developed at a given moment, denoted as Δσv, decays with εir towards different residual values during subsequent ML. With the TESRA type, Δσ v decays eventually totally and the strength during ML at constant ε̇ is essentially independent of ε̇. With the Combined type, Δσv decays with εir like the TESRA type, but it does not decay totally. So, the strength during ML at constant ε̇ increases with ε̇ like the Isotach type. With theP&N type, found latest, a positive value of Δσv decays towards a negative value. So, the strength during ML at constant ε̇ decreases with an increase in ε̇ . The viscosity type tends to change with εir: e.g., from Isotach toward TESRA and from TESRA toward P & N. A general mathematical expression that can describe these four viscosity types and transitions among them is proposed. Numerical simulations of typical drained triaxial compression tests of geomaterials based on a non-linear three-component model incorporating the general expression of the viscous stress are presented. The viscosity type is controlled by at least, grading characteristics and particle shape. Copyright © 2005-2009 National Institute of Informatics.
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Rate effect
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