VARIOUS VISCOSITY TYPES OF GEOMATERIALS IN SHEAR AND THEIR MATHEMATICAL EXPRESSION

摘要

References(45) Cited-By(1) 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, ε, and performing sustained loading during otherwise monotonic loading (ML) at a constant ε and also by performing ML tests at different constant values of ε. Four basic viscosity types, Isotach, Combined, TESRA (or Viscous 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, εir. So, the strength during ML at a constant ε increases with ε. 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 TESRAtype, Δσv decays eventually totally and the strength during ML at constant ε is essentially independent of ε. 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 ε increases with ε like the Isotach type. With the P & N type, found latest, a positive value of Δσv decays towards a negative value. So, the strength during ML at constant ε decreases with an increase in ε. 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.