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. © 2015 The Authors. International Journal for Numerical and Analytical Methods in Geomechanics published by John Wiley & Sons Ltd.
Highlights
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 behaviour of soils
This paper extends the S-CLAY1S model [12] using the framework of logarithmic contractancy [16] to include some flexibility in the shape of the yield surface
The normalized vertical separation eN ÀeΓ λiÀκ to the normal compression line (NCL) in the e-ln p′ space at critical state with the nL value is presented in Stress paths M=1
Summary
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 behaviour of soils. Especially for settlement prediction, horizontal displacements are generally not well matched, for example, [15] Those differences may be attributed to the shape of the yield surface (i.e. associates with flow rule), or to the horizontal/vertical stress ratio predicted by the model for compression loading. The framework is based on curve fitting of experimental results of the contractancy (compressive volumetric strain, εv) during drained shear at constant mean effective stress (p′) of normally consolidated clays. The contractancy parameter can be related to the coefficient of earth pressure at rest for normally consolidated conditions, K0NC, the undrained shear strength, cu, or the stiffness under shearing stress paths In this way, the proposed model, called E-SCLAY1S, extends the predictive capabilities of the S-CLAY1S model, while including just an additional parameter with clear physical meaning. The model is validated against laboratory tests on two clays, namely, Kaolin clay and Santa Clara clay (Section 5) and some discussion and conclusions are provided
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