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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]

A change in temperature induces thermo-osmosis (T-O) and thermofiltration (T-F) effects in soils, which can influence consolidation under certain conditions. Whether such conditions are met is not always known a priori. Therefore, this paper first develops a coupled model to assess these effects on the thermohydromechanical coupled behavior of saturated soils. The proposed model, which incorporates the extended Darcy's law and Fourier's law, is implemented in the finite-element method (FEM) solver OpenGeoSys version 6.3.3. To determine when T-O/T-F effects become relevant in an analysis, two characteristic numbers are then derived from the extended governing equations, which can be directly expressed by readily available soil and water parameters. Both theoretical and numerical analyses were conducted, and the results indicate that the T-F effect has little influence on heat transfer in typical soils, while the T-O effect appears to be significant for both sandy and clayey soils, provided the T-O coefficient exceeds 4.3 × 10-12 m²=ðs · KÞ. The T-O effect could even lead to the development of negative excess pore water pressure (PWP) and, consequently, soil compression, with relevance for the stability of geotechnical facilities subjected to temperature gradients. It is thus inferred that the T-O coefficient should be measured in conjunction with related necessary experimental work, in addition to soil permeability, to determine whether the T-O effect should be treated with caution. [ABSTRACT FROM AUTHOR]

The writers appreciate the discussers' recognition of the pioneering and novel nature of the original work, which provides a unified effective stress equation for all types of soils under all saturation conditions. However, the discussers fail to appreciate the importance of the roles of soil water adsorption mechanisms in soil water retention and effective stress, given the ample experimental evidence presented in our work and other previously published work. Instead, they raise some points, which are academically thought-provoking notions that are largely reflections of the misunderstanding of the importance of the soil sorptive potential (SSP) concept and the roles of SSP in the effective stress in soils, as detailed subsequently, following the order outlined by the discussers. The discussers consider that the sole mechanical energy in soil water is capillary pressure as they state "That [capillary water] is presumably why many researchers have previously suggested that capillary water, solely, plays a role in the mechanical behavior of unsaturated soil.". [Extracted from the article]

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]

A clayey soil is an electrically charged porous medium whose behavior is sensitive to the variations in the composition and concentration of pore water. Pronounced physicochemical interaction can occur between the solid particle and the pore water so that the clayey soil shows strong chemomechanical coupling effects and complex mechanical behaviors. If the degree of saturation varies the pore-water composition and concentration can also vary, resulting in intensive physicochemical effects in the soil. In this paper, a conceptual constitutive model for unsaturated soils is proposed to explain the influence of pore-fluid chemistry on the chemomechanical behavior of unsaturated clayey soils. A new intergranular stress which can effectively account for the physicochemical effects including osmosis, capillarity, and adsorption is introduced as the stress-state variable. The formulation of the proposed model can lead to a remarkable unification of the experimental results obtained under complex chemomechanical loading conditions. The proposed model is validated by comparing the theoretical calculations with the experimental results. It is shown that the proposed model is capable of addressing the effect of water content, concentration and species variation on the mechanical behavior of the clayey soil. [ABSTRACT FROM AUTHOR]

Shear wave propagation in soil is a physical phenomenon and has been used widely for monitoring and seismic property assessment in geotechnical engineering. Shear wave velocity Vs and small-strain shear modulus G0 are the key parameters in defining material response to various dynamic loadings. To date, the dependencies of Vs and G0 on saturation, especially in high suction range, are still not well understood because of the limited testing methodology and experimental evidence. In this study, the authors present a new laboratory instrumentation of measuring shear wave propagation in different types of unsaturated soils. Low relative humidity and water mist injection environment are used for measuring shear wave velocity under both drying and wetting conditions. Bender element technique was used to measure the shear wave responses. Step function was used as excitation, and determination of a first arrival time was identified and consistently used for all shear wave measurements. Shear wave evolution and the calculated Vs and G0 with varying volumetric water content under zero total stress condition along drying and wetting are presented. The effects of different soil-water regimes on the evolution of G0 are examined. It is found that Vs or G0 depends highly on soil types, saturation, and drying/wetting state. Parameter Vs or G0 is the lowest when a soil is saturated and the highest when it is dry—varying from tens of meters per second for Vs or a few megapascals for G0 at full saturation for all soils to up to 1,800 m=s of Vs or 2 GPa of G0 in clayey soil at dry state. The variability of Vs or G0 on soil type becomes more pronounced as soil has more clayey materials. It is also identified that hydraulic hysteresis of Vs or G0 is prominent only in the capillary water retention regime for all types of soil. [ABSTRACT FROM AUTHOR]

This paper extends Olson’s solution for one-dimensional consolidation under time-dependent loading with the assumption of constant coefficient of consolidation, to those with varying loading-dependent coefficients of consolidation. The investigation first presents the experimental study on a series of one-dimensional consolidation tests with various loading rate. Subsequently, the viscoelastic theory was applied to estimate the consolidation settlement and compared with the experimental results. Four consolidation tests with different loading rates were performed on three types of remolded clay soils with various plasticity indices to evaluate loading rate effects on the consolidation settlement. After explicitly performing the falling head permeability test at various stages during the conventional consolidation tests, the variation of coefficient of consolidation with external pressure was established and converted to the relationship between the coefficient of consolidation and the time of the corresponding pressure applied on the specimens for each loading rate test. The hereditary integral of viscoelastic theory was then applied to predict the settlement curve with time for each loading rate test. The findings indicate that the theoretical predictions using the loading-dependent coefficients of consolidation and experimental results in term of consolidation settlement are in good agreement. [ABSTRACT FROM AUTHOR]