A destructuration theory and its application to SANICLAY model

Abstract

SUMMARYMany natural clays have an undisturbed shear strength in excess of the remoulded strength. Destructuration modeling provides a means to account for such sensitivity in a constitutive model. This paper extends the SANICLAY model to include destructuration. Two distinct types of destructuration are considered: isotropic and frictional. The former is a concept already presented in relation to other models and in essence constitutes a mechanism of isotropic softening of the yield surface with destructuration. The latter refers to the reduction of the critical stress ratio reflecting the effect of destructuration on the friction angle, and is believed to be a novel proposition. Both the types depend on a measure of destructuration rate expressed in terms of combined plastic volumetric and deviatoric strain rates. The SANICLAY model itself is generalized from its previous form by additional dependence of the yield surface on the third isotropic stress invariant. Such a generalization allows to obtain as particular cases simplified model versions of lower complexity including one with a single surface and associative flow rule, by simply setting accordingly parameters of the generalized version. A detailed calibration procedure of the relatively few model constants is presented, and the performance of three versions of the model, in descending order of complexity, is validated by comparison of simulations to various data for oedometric consolidation followed by triaxial undrained compression and extension tests on two structured clays.

Application of an Anisotropic Constitutive Model for Structured Clay to Seismic Slope Stability

“…In this way, the developed model can be simplified back to the MCC model. The present formulation does not include some of the constitutive features that existed in earlier work of Taiebat et al (2010), such as the nonassociated flow rule and frictional destructuration mechanism, trading slightly less accuracy in simulations for simplicity. The resulting model is simple and rational, yet significantly improves the MCC model in describing some essential features of response in natural clays.…”

“…The kinematic hardening rule for the internal variable α is based on the distance of back stress ratio α from its bounding image α b , which in turn is defined by an attractor term r=x as (Dafalias et al 2006;Taiebat et al 2010)…”

“…A slight difference of notation is adopted here from the work of Taiebat et al (2010), whereas instead of p 0 and p 0d , the notations were p à 0 and p 0 , respectively, were used. With this new definition of p 0 , Eq.…”

“…(8)- (10) is a classical approach of isotropic destructuration introduced earlier by Nova (1992) and Gens and Nova (1993). In Taiebat et al (2010), in addition to the present isotropic destructuration mechanism that is in effect an isotropic-softening constitutive feature, an additional frictional destructuration mechanism was introduced that addressed the possible collapse of the critical state stress ratio M in the foregoing destructuration plastic strain rate of Eq. (10).…”

“…FLAC 3D is a dynamic code that uses an explicit time-integration scheme, coupled solid-pore fluid interaction, and large strain formulation and is well suited for solving dynamic stability problems. Constitutive behavior of the soil matrix is characterized in this work by a simplified version of the simple anisotropic clay (SANICLAY) plasticity model (Dafalias 1986;Dafalias et al 2006;Taiebat et al 2010). This model accounts for a number of important aspects of material response, such as initial and induced anisotropy and destructuration, to capture the strain softening that exists in some marine clays.…”