An anisotropic elastoplastic model for soft clays based on logarithmic contractancy

Abstract

SUMMARYA new constitutive model for soft structured clays is developed based on an existing model called S-CLAY1S, which is a Cam clay type model that accounts for anisotropy and destructuration. The new model (E-SCLAY1S) uses the framework of logarithmic contractancy to introduce a new parameter that controls the shape of the yield surface as well as the plastic potential (as an assumed associated flow rule is applied). This new parameter can be used to fit the coefficient of earth pressure at rest, the undrained shear strength or the stiffness under shearing stress paths predicted by the model. The improvement to previous constitutive models that account for soil fabric and bonding is formulated within the contractancy framework such that the model predicts the uniqueness of the critical state line and its slope is independent of the contractancy parameter. Good agreement has been found between the model predictions and published laboratory results for triaxial compression tests. An important finding is that the contractancy parameter, and consequently the shape of the yield surface, seems to change with the degree of anisotropy; however, further study is required to investigate this response. From published data, the yield surface for isotropically consolidated clays seems 'bullet' or 'almond' shaped, similar to that of the Cam clay model; while for anisotropically consolidated clays, the yield surface is more elliptical, like a rotated and distorted modified Cam clay yield surface.

Undrained expansion of a cylindrical cavity in clays with fabric anisotropy: theoretical solution

“…To validate the semi-analytical solution, finite element simulations have been performed using the commercial code PLAXIS 2D 2015 [2]. The S-CLAY1 model has been implemented as User-defined soil model in PLAXIS, using an automatic substepping in combination with a modified Newton-Raphson integration scheme [27,28].…”

Numerical simulations of the reuse of piled raft foundations in clay

“…More theoretical formulations were later documented by Sekiguchi [43], Adachi and Oka [1], and Borja and Kavazanjian [7]. Highly advanced constitutive models have recently been developed to capture various soil characteristics including soil destructuration, anisotropy (due to deposition history) and cyclic loading [19,20,24,26,31,34,35,41,49,55,57,59,61]. This is not intended to be an exhaustive list, however, and more in-depth discussion on this topic is available in Liingaard et al [33].…”

A Constitutive Model for Soft Clays Incorporating Elastic and Plastic Cross-Anisotropy

“…The elastic behavior in the model is formulated as isotropic, with elastic increments of volumetric and deviatoric strains given by the same expressions as in MCC: where is a stress-dependent elastic bulk modulus ( ). The model has traditionally been implemented assuming a constant Poisson’s ratio, [ 3 , 14 ]. Thus, the shear modulus is related to the elastic bulk modulus , and is also stress dependent, instead of being constant.…”

“…The main advantages of the S-CLAY1S model are: (i) its relatively simple model formulation; (ii) its realistic prediction; and, most importantly; (iii) the fact that model parameter values can be determined from standard laboratory tests using well-defined methodologies [ 10 ]. S-CLAY1S was chosen to keep the model simple, but there are more advanced constitutive models for soft clays that, for example, introduce some flexibility in the shape of the plastic potential [ 14 ] or use a non-associated flow rule [ 18 , 19 ]. Some other advanced features of clay behavior, such as creep [ 20 ] or small-strains [ 21 ], have not been here considered either.…”