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

Abstract

The time eŠects on the stress-strain behaviour of geomaterial consist of eŠects of loading rate and ageing. The positive ageing eŠects are analysed based on the results from drained triaxial compression (TC) tests on cement-mixed kaolin and well-graded gravelly soil and incorporated into a non-linear three-component model that can simulate the elasto-viscoplastic behaviour of geomaterials. The inviscid yielding is controlled by the inviscid yield stress that develops basically by irreversible straining and time elapsing following, respectively, a basic inviscid strain-hardening function and an ageing function. The inviscid yield stress may develop additionally by positive interaction between ageing and inviscid yielding following an interaction function, which expresses an additional strength gain by longer ageing at higher shear stress levels. Positive interaction eŠects are damaged by subsequent irreversible straining following a damage function. These functions are formulated based on experimental results. Illustrative model simulations are presented to describe the structure of the proposed model. The model is validated by simulating drained TC tests exhibiting signiˆcant eŠects of loading rate and ageing.

Ageing Effects on the Yielding Characteristics of Cement-Mixed Granular Materials

“…It has been shown that, when the conˆning pressure isˆxed and only a single stress parameter is variable (e.g., the deviator stress or the principal stress ratio), this model can accurately simulate elasto-viscoplastic behaviour of a wide variety of geomaterials not exhibiting ageing eŠects during and after complex and arbitrary loading histories (Tatsuoka et al, , 2008aDi Benedetto et al, 2002;Kongkitkul et al, 2008). Moreover, the model can easily incorporate ageing eŠects via those on elastic and plastic components (Tatsuoka et al, 2008b(Tatsuoka et al, , 2008c. The model is only brie‰y described below, as its detailed description under general stress conditions is not the primary purpose of this paper.…”

“…On the other hand, to describe the other viscous property types (i.e., TESRA, Combined and P and N), eŠects of previous loading history need to be taken into account by introducing the decay function gdecay, which is a function of the current irreversible strain and a strain history parameter controlling the decay rate, as described in details by Di and Tatsuoka et al (2002Tatsuoka et al ( , 2008a. The previous studies Tatsuoka et al, 2008b) showed that the viscous property of the cement-mixed gravelly soil used in the present study is the Isotach type in the pre-peak regime while it changes toward the TESRA type in the postpeak regime. In the following part of this paper, as only the yielding characteristics of cement-mixed GM in the pre-peak regime is analyzed, only the Isotach type viscous property is dealt with.…”

“…4 )). In this illustrative case, no interaction eŠect between inviscid yielding and ageing is introduced: i.e., the s f -e ir relation for a given t c is unique, independent of loading history (Tatsuoka et al, 2008b). In Fig.…”

“…The time eŠects, which aŠect the yielding characteristics of cement-mixed GM, comprise the following two components (Table 1; Tatsuoka et al, 2003Tatsuoka et al, , 2008b, c): a) Ageing eŠects: deˆned as time-dependent changes in the intrinsic stress-strain properties, including peak strength, elasticity, yielding and viscous properties. The ageing eŠects can be expressed as a function of time (tc) having a speciˆcally deˆned origin.…”

“…1) are aŠected by ageing. Interactions between ageing eŠects (as a function of time tc) and the yielding of plastic body P are taken into account, as described in Tatsuoka et al (2008b) and later in this paper.…”