Various Viscosity Types of Geomaterials in Shear and Their Mathematical Expression

Abstract

The viscous properties, or loading-rate eŠects 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, ·e, and performing sustained loading during otherwise monotonic loading (ML) at a constant ·e and also by performing ML tests at diŠerent constant values of ·e. 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, e ir and its rate, ·e ir . So, the strength during ML at a constant ·e increases with ·e. With the other three types, the viscous stress increment that has developed at a given moment, denoted as Ds v , decays with e ir towards diŠerent residual values during subsequent ML. With the TESRA type, Ds v decays eventually totally and the strength during ML at constant ·e is essentially independent of ·e. With the Combined type, Ds v decays with e ir like the TESRA type, but it does not decay totally. So, the strength during ML at constant ·e increases with ·e like the Isotach type. With the P & N type, found latest, a positive value of Ds v decays towards a negative value. So, the strength during ML at constant ·e decreases with an increase in ·e. The viscosity type tends to change with e ir : 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.

Effect of Particle Shape on the Mechanical Behavior of Natural Sands

“…Though some authors provide numerical roundness values (e.g. Rouse et al, 2014, Yoshimoto et al, 2012Tatsuoka et al, 2008), in geotechnical research authors more commonly describe roundness qualitatively.…”

Modelling of Ageing Effects on the Elasto-Viscoplastic Behaviour of Geomaterial

“…So, the strength during ML at constant ·e decreases with an increase in ·e. Enomoto et al (2007), and Tatsuoka et al (2008) reported that the four viscosity types described above can be classiˆed by the viscosity type parameter, u, deˆned as:…”

“…The viscous property is a function of instantaneous irreversible (or visco-plastic) strain rate ( ·e ir or ·e vp ) and other relevant parameters, not by time Tatsuoka et al, 2002Tatsuoka et al, , 2003Tatsuoka et al, , 2008Tatsuoka, 2004. Geomaterials in theˆeld have been aged at early or late stages of diagenetic process on the geological or engineering time scale, or in between.…”

“…In the present study, the non-linear three-component model ( Fig. 2(a)) is employed based on the fact that this model can simulate laboratory stress-strain tests on geomaterials that exhibit various viscous responses (e.g., Di Benedetto et al, , 2005Tatsuoka et al, 2002Tatsuoka et al, , 2004Tatsuoka et al, , 2008. According to this model, the stress (i.e., the eŠective stress), s, is obtained by adding the viscous component, s v , to the inviscid (or rate-independent) component, s (Fig.…”

Viscous Behaviour of Unbound Granular Materials in Direct Shear

“…To this end, the time-eŠects on the stress-strain behaviour of geomaterial should be understood correctly and properly. Even if the in‰uence of pore water pressure changes is not involved, the following two types of time eŠects should be taken into account (e.g., Di Benedetto et al, 2005;Tatsuoka et al, 2008): the ageing eŠect, which can be deˆned as``changes with time in the intrinsic stress-strain properties due to time-dependent changes in interface and/or internal particle properties caused by a physico-chemical process'' and the``viscous or loading rate eŠect'', which can be attributed primarily to the``viscous deformation and sliding at inter-particle contact points and its eŠects on the structural stability of a given soil mass''. The viscous or loading rate eŠect is the topic of this paper.…”