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In this paper, a modified/extended rotational hardening (RH) rule is applied to the nonassociated simple anisotropic constitutive model, SANICLAY-D, for clayey soils. In the proposed model, the destructuration mechanism, as well as zero and nonzero fabric anisotropy at critical state (CS), are considered. A detailed model formulation with the RH rule that yields a unique CS in the e-ln(p′) space is presented including an appropriate form of the relatively simple substepping integration algorithm. In addition, the model is implemented into ABAQUS finite-element software using a User-defined Material (UMAT) subroutine and used in the simulation of various experimental tests. The modified SANICLAY-D model (SANICLAY-MD) is meticulously calibrated step by step for Saint-Alban sensitive soft clay. Drained and undrained triaxial tests after various consolidation paths as well as the direct simple shear (DSS) test are simulated for Saint-Alban and Bothkennar clays as a boundary value problem. Simulation results approve the SANICLAY-MD model's performance in the prediction of the natural soil behavior. Results show that neglecting the effect of fabric anisotropy at CS and destructuration of natural clays can lead to inaccurate prediction in the constitutive modeling of intact soft soils. [ABSTRACT FROM AUTHOR]

Physiochemical forces of attraction and repulsion from clay mineralogy of an expansive soil during hydration contribute to the macro swell behavior of expansive soils. In this research, diffuse-double-layer (DDL) theory–related electrostatic forces from individual clay minerals of an expansive soil and their influence on soil swelling were studied. A fundamental approach for estimating swell potentials using the DDL model is proposed here for improved characterization of soil swelling potential. As a part of this research, 14 natural expansive clays were characterized and studied by performing basic soil characterization and clay mineralogy studies, followed by one-dimensional swell strain and swelling pressure tests. Clay mineralogy data were used to estimate total DDL thicknesses, which eventually transpire as adsorbed layers during the swelling process. Assumptions with respect to clay mineral crystalline alignment and orientation of clay particles were made in order to estimate adsorbed DDL thicknesses. Estimated DDL thicknesses were then converted to DDL strains, which were later correlated with the measured swell potentials of the present soils. Strong correlations between DDL-based strains and measured swell potentials are observed, indicating the importance of using DDL concepts in the estimation of swell properties. Further refinements of the modeling and model coefficients are to be conducted in the progressive studies for better prediction of the swell behavior of soils. [ABSTRACT FROM AUTHOR]