Abstract
Natural clays exhibit a significant degree of anisotropy in their fabric, which initially is derived from the shape of the clay platelets, deposition process and one-dimensional consolidation. Various authors have proposed anisotropic elastoplastic models involving an inclined yield surface to reproduce anisotropic behavior of plastic nature. This paper presents a novel constitutive model for soft structured clays that includes anisotropic behavior both of elastic and plastic nature. The new model incorporates stress-dependent cross-anisotropic elastic behavior within the yield surface using three independent elastic parameters because natural clays exhibit cross-anisotropic (or transversely isotropic) behavior after deposition and consolidation. Thus, the model only incorporates an additional variable with a clear physical meaning, namely the ratio between horizontal and vertical stiffnesses, which can be analytically obtained from conventional laboratory tests. The model does not consider evolution of elastic anisotropy, but laboratory results show that large strains are necessary to cause noticeable changes in elastic anisotropic behavior. The model is able to capture initial non-vertical effective stress paths for undrained triaxial tests and to predict deviatoric strains during isotropic loading or unloading.
Highlights
The stress–strain response of natural soft clays is influenced by geological processes that occurred long time ago and their response is much more complicated and unpredictable than that of any other man-made construction material
Natural soft clays exhibit a significant degree of anisotropy in their fabric, which initially is derived from the shape of the clay platelets, deposition process and one-dimensional consolidation
For the sake of simplicity, the mathematical formulation is presented in bonds is reproduced using intrinsic and natural yield surfaces [12] and a hardening law the following in triaxial stress space, which can be used only to model the response of cross-anisotropic describing destructuration as a function of plastic straining
Summary
The stress–strain response of natural soft clays is influenced by geological processes that occurred long time ago and their response is much more complicated and unpredictable than that of any other man-made construction material. Extensive experimental testing of soils under different stress paths and conditions as well as the increase in computing power has led to the development of advanced constitutive models that reproduce more accurately the mechanical behavior of soils. Some of these advanced constitutive models incorporate plastic anisotropy using a rotated and distorted elliptical yield surface [2,3,4,5]. The MELANIE model does not consider two important features of soft clay behavior: evolution of plastic anisotropy with plastic straining and stress-dependent elastic stiffness. A and r subscripts indicate axial and radial principal directions, respectively
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