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Bentonite is utilized as a barrier material in high-level nuclear waste repositories due to its superior low permeability and swelling properties. However, its engineering properties are influenced by the chemical composition of the infiltrating pore water during operation. Understanding the effect of salt solution on the mechanical properties of bentonite is crucial for evaluating the performance of buffer and backfill barriers in deep geological repositories for nuclear waste. In this study, various concentrations and types of salt solutions were used to treat Na-bentonite samples, which were then subjected to free swell test, no loading swelling ratio test, Atterberg limits test, compaction test, and analysis of the content of exchangeable cations. The results showed that the content of counterbalance cations changed significantly after the addition of salt solution, and the decrease in free swelling rate increased gradually with the increase of solution concentration. The effect of different types of salt solutions on swelling was primarily determined by the type of cation that governs charge level and hydration capacity. The inhibition of the free swelling rate was stronger for high-concentration low-valence salt solution than that for low-concentration high-valence one. Bentonites undergoing cation exchange exhibited a decreased plasticity index, a decreased maximum dry density, and an increased optimum water content. This was mainly due to the cation exchange that occurred between bentonite layers under the action of the salt solution, which affected the crystal layer structure, double electric layer structure, and intergranular stress. Finally, the van’t Hoff equation was used to quantitatively characterize the differences in swelling in the test results. [ABSTRACT FROM AUTHOR]

Determining osmotic suction from the electrical conductivity (EC) of soil pore water was widely reported in the literature. However, while dealing with unsaturated soils, they do not have enough soil pore water to be extracted for a reliable measurement of EC. In this paper, the chilled-mirror dew-point hygrometer and contact filter paper method were used to determine the total and matric suctions for low-plasticity soils with different salinities (0.05‰, 2.1‰, and 6.76‰). A new piecewise function was proposed to calculate the osmotic suction, with the piecewise point corresponding to the first occurrence of precipitated salt in mixed salt solutions (synthetic seawater). EC, ion and salt concentrations used for osmotic suction calculation were transformed from the established relationships of mixed salt solution instead of experimental measurement. The calculated osmotic suction by the proposed equation and the equations in the literature was compared with the indirectly measured one (the difference between the measured total and matric suctions). Results showed that the calculated osmotic suction, especially the one calculated using the proposed function, was in fair agreement with the indirectly measured data (especially for specimens with higher salinity of 6.76‰), suggesting that the transformation of EC and concentrations from the established relationship is a good alternative to direct measurement for low-plasticity soil. In particular, the proposed method could be applied to unsaturated low-plasticity soils which do not have enough soil pore water for a proper EC measurement.

Salinity-induced soil degradation is a significant challenge in coastal reclamation areas, impacting agricultural productivity and infrastructure development. Variations in soil compression and deformation caused by changes in salinity warrant further investigation, particularly for agricultural applications. This study explores the relationship between soil pore water salinity and compressibility by conducting isotropic compression tests on salinized unsaturated agricultural soils treated with distilled water, 0.5 mol/L and 1 mol/L sodium chloride (NaCl) and calcium chloride (CaCl 2) solutions. The results demonstrate that the type and concentration of salts significantly affect the compression behavior of these soils. The constitutive parameters were calibrated based on the experimental data. To account for osmotic suction, Barcelona Basic Model (BBM) was adjusted. The findings indicate that as pore water salinity increases, soil compressibility decreases, reflected by a compression index (C c), and higher pre-consolidation stress (p y). This modification aimed to quantify the impact of pore water salinity on soil compression. To validate the constitutive model, a numerical analysis of an isotropic compression test was carried out. This study contributes to our understanding of the isotropic compression behavior of coastal saline soil, proposes a constitutive framework for predicting soil responses under different salt conditions, and provides theoretical support for engineering construction in coastal reclamation areas. • Isotropic compression test were performed on salinized unsaturated soils. • The compression index decreased with increasing pore water salinity. • Osmotic suction was considered in the Barcelona Basic Model (BBM). • The model can be well applied in simulating saline soil compression behavior. [ABSTRACT FROM AUTHOR]

In order to clarify the suction characteristics of unsaturated clay under different conditions of water and salt, taking soil in western Jilin province, China as the research object, the suctions (matrix suction and osmotic suction) of samples with different water content, salt type, and salt content were determined by filter paper method. The results indicate that salt type and content have insignificant influence on the matrix suction. With the increase of water content, the matrix suction decreases at different rates in different suction regimes. When water content is constant, the osmotic suction increases with the increase of salt content, and under the condition of a constant salt content, the osmotic suction first increases and then decreases with the increase of ion concentration of the pore water, and can reach tens of MPa. The concept of suction equilibrium water content is proposed. When water content of sample is higher than this value, the magnitude of osmotic suction will always be greater than that of matrix suction. This indicates the necessity to consider osmotic suction in the presence or change of salt in soil. The applicability of the traditional models of matrix suction and osmotic suction in the full suction range of clay is discussed, and it is found that the traditional models cannot make a full explanation to the variation in suction. Based on the experimental data, an improved van Genuchten matrix suction model and an osmotic suction model, transformed by the Planck blackbody radiation formula, are proposed. [ABSTRACT FROM AUTHOR]

As most previous studies have neglected the positive influence of salinity (osmotic suction) on most coastal soils in Australia, the design of transport infrastructure involving these soils has often been overly conservative. In this study, a laboratory approach based on direct shear testing was explained to determine the stress–strain behavior of compacted coastal silty clay (CL) at different levels of osmotic suction generated by various salinity (NaCl) concentrations. A broad data set for a total of 147 direct shear tests conducted on remolded and recompacted test specimens at seven different initial matric suction conditions was analyzed to develop a semiempirical model that captures the effect of osmotic suction on the soil shear strength. The results suggested that the greater the initial matric suction, the more pronounced the role of osmotic suction. The proposed semiempirical model was governed by an electrical conductivity relationship with the osmotic suction generated by soil salinity. A new parameter χ2 was introduced to quantify the role of soil salinity in the apparent soil shear strength corresponding to different levels of osmotic suction. When this novel relationship was coupled with the conventional matric suction theory, the overall unsaturated shear strength of a saline soil could be properly evaluated, as proven by the close proximity of the predictions to the measurements. [ABSTRACT FROM AUTHOR]

Copyright of China Sciencepaper is the property of China Sciencepaper and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Investigation of osmotic suction effects on the volume change behavior of clay is of great importance in evaluating the performance of engineering barrier in deep geological repository for the disposal of high-level radioactive waste. From the effective stress principle point of view, the linear relationship between the concentration of salt solution and osmotic suction described by the common van't Hoff equation is not consistent with the experimental results, because the salt solution (or osmotic suction) effect on the swelling behavior and compressibility became insignificant when the concentration of salt solution was higher than 2.0 M. Meanwhile, the osmotic suctions described by Lang (Aust J Chem 20(9):2017–2023, 1967), Rao et al. (Géotechnique 56(10):707–713, 2006) and Witteveen et al. (Géotechnique 63(3):244–255, 2013) are also not consistent with the effective stress principle. In this study, the influence of osmotic suction on swelling behaviors was explained from the crystalline swelling and the double-layer swelling for specimens with a void ratio higher than 0.5. According to the experimental observations, a new effective stress equation was proposed with consideration of osmotic suction effects for the compacted GMZ01 bentonite specimen with a void ratio higher than 0.5. Finally, the proposed equation was verified based on the observations of the swelling and oedometer tests conducted on as-compacted GMZ01 bentonite specimens. [ABSTRACT FROM AUTHOR]

This paper presents a new designed 1-D free swelling test of compacted bentonite in glass tubes to simulate the process by which the bentonite cushion in the nuclear waste disposal reservoir swells and squeezes into the crack after absorbing the fissure water from surrounding rock. Deionized water and NaCl, Na2SO4, CaCl2 solutions with different concentrations were used as soaking solutions, and the change of the specimen height with time was recorded until the swelling completed. The effects of initial dry density, initial water content, and soaking solution concentration and type on the swelling deformation of bentonite were analyzed. Results show that the maximum swelling strain, almost independent from initial water content, increases with the initial dry density. The increase in the concentration of the salt solution reduces the free swelling deformation, and the degree of inhibition is related to the type of the salt solution. The effect of the concentration and type of the salt solution on swelling property can be uniformly reflected by the osmotic suction that acts as an additional stress applied on bentonite and is quantified as osmotic pressure item of the total effective stress proposed previously that controls the swelling strain of compacted bentonite. Then, the maximum swelling strains of the compacted bentonite under different soaking solutions in 1-D free swelling test can be predicted by a uniform power-law relationship with the total effective stress. [ABSTRACT FROM AUTHOR]

Osmotic suction affects the mechanical properties of the clay and exists as long as the solute is present in pore water of soil. Determination of osmotic suction of pore solution is significant for quantitatively explaining the mechanical behaviors of clay in saline solution. This paper aims to introduce a calculation method to determine the osmotic suction of saline solutions and the application of the osmotic suction to quantify the mechanical behaviors of clay in saline solutions. Osmotic coefficient as the bridge connecting ion concentration and osmotic suction was calculated by a simplified half-empirical equation and verified by published experimental data. Then the osmotic suctions were achieved using the calculated osmotic coefficients, and two filter paper methods were carried out to verify the calculated results. The consistency between the experimental results and the calculated ones proved the correctness of the proposed method for calculating the osmotic suction. A step further, the mechanical behaviors of clay in saline solutions were explained and quantified from the microscopic with the concept of microstructural effective stress and the macroscopic with the concept of modified effective stress, both related to the osmotic suctions. [ABSTRACT FROM AUTHOR]

Numerous studies have shown that the invasion of the chemicals plays an important role on the geomechanical properties of the soil. This article aims to investigate the shear behavior of contaminated soil by laboratory tests and develop an extended shear strength model on the basis of the experimental results. In order to explicitly evaluate the effect of solution concentration on the shear strength behavior of soil, the remolded samples of kaolinite mixed with different concentrations of CuCl2 solutions were prepared to carry out a series of consolidated-undrained triaxial shear strength tests. The results indicate that different CuCl2 solution concentrations have significant influence on the shear strength property of kaolinite. With the increase of CuCl2 solution concentration, the shear strength of soil displays a declining tendency, and the strength properties including cohesion and internal friction angle are also reduced, which indicates the Cu (II) that existed in the soil samples has deteriorated the soil strength strongly. Based on the experimental results, an extended Mohr–Coulomb strength model for contaminated soils has been proposed by introducing osmotic suction as a macro variable parameter. The conclusions in this study can provide reference for pollution prevention of existing and future foundations. [ABSTRACT FROM AUTHOR]

Bentonite is usually selected as the buffering barrier material for high-level nuclear waste repository due to its characteristics of high expansibility and low permeability, yet the swelling properties are influenced by the saline solution existing in the fissures of surrounding rocks. Quantifying the effects of saline solution concentration on the swelling property of compacted bentonite is significant for assessing the security of engineering barrier used to dispose high-level radioactive waste. In this study, the modified effective stress incorporating with osmotic suction generated from saline solution is proposed to depict the volume changes for bentonite in saline solution with different concentrations by a unique equation. The osmotic suctions are calculated with the simplified Debye-Hückel equation and the results are validated by comparing with the experimental data in other literatures. The published experimental data prove the uniform relationship between the volume change and the modified effective stress in saline solution with different concentrations. Therefore, the quantitative predictions of volume change of bentonite in saline solution with different concentrations are presented using the modified effective stress concept. [ABSTRACT FROM AUTHOR]

Abstract Knowledge of the peak shear strength of compacted bentonites is of fundamental importance to high-level nuclear waste repositories, as it forms the basis of the analysis of repository stability. The shear strength properties of GMZ bentonites are throughout investigated by undrained direct shear tests with different concentrations of NaCl solutions, and are explained in the light of the modified effective stress concept, which takes into consideration of the osmotic suction. The modified effective stress concept is expressed as p ' = p + π (p / π) D s-2, incorporated with the normal stress (p) and osmotic suction (π) based on the bentonite surface fractal model. The peak shear strength behavior of GMZ bentonites in NaCl solutions appears to be explained satisfactorily by the modified effective stress. According to the Mohr-Coulomb criterion, the peak shear strength of bentonites saturated by distilled water and NaCl solutions is expressed by the same unique line in the τ - p ' plane. GMZ bentonite has the same values of the peak friction angle and the peak cohesion in distilled water and NaCl solutions of different concentrations. Highlights • Peak shear strength of bentonite expressed by modified effective stress according to the Mohr-Coulomb criteria • A modified effective stress expressed as p ′ = p + (p / π) D s ‐2 π , incorporating with osmotic suction (π) • The surface fractal dimension (D s) of GMZ bentonite measured using the nitrogen adsorption isotherm. [ABSTRACT FROM AUTHOR]

Investigation on influences of cyclic salinization-desalinization processes on clay is of great importance for evaluation of the behavior of engineering barrier in deep geological repository for disposal of high-level radioactive waste. In this study, one-dimensional free swelling tests were conducted on densely compacted GMZ01 bentonite specimens, which has an initial dry density of 1.7 Mg/m 3 , with cyclically infiltration of NaCl, CaCl 2 or KCl solution at different concentrations and de-ionized water. Results show that the volume change of the compacted clay could be influenced by concentrations and cation types of solutions, as well as number of salinization-desalinization cycles during the salinization-desalinization processes. The total swelling strain of GMZ01 bentonite specimens measured on the first salinization with salt solutions at a same concentration follows an order: NaCl > CaCl 2 > KCl. This observation could be explained by the influences of basal space, DDL theory and K-linkage. A cation with higher replacing power can be replaced by another cation with lower replacing capacity when it has a higher concentration in the pore solution. The concentration effect on the swelling behavior of GMZ01 bentonite was explained using the concept of osmotic suction for specimens initially infiltrated with NaCl solutions. For specimens initially infiltrated with CaCl 2 solutions, in addition to the osmotic suction effect, the distance between the unit layers of montmorillonite also played a role in explaining the swelling behavior. The swelling behavior of specimens initially infiltrated with KCl solutions could be explained by the strong K-linkage. [ABSTRACT FROM AUTHOR]

Pore solution salinity has important bearing on engineering behavior of marine sediments as they influence electrochemical stress ( A- R) and differential osmotic stress (∆ π) of the salt-enriched clays. The electrochemical stress ( A- R) is contributed by van der Waals ( A) attraction and diffuse ion layer repulsion ( R) , while the differential osmotic stress (∆ π) is governed by the differences in dissolved salt concentrations in solutions separated by osmotic membrane. The paper examines the relative influence of differential osmotic stress (Δ π) and electrochemical stress ( A- R) on the consolidation behavior of slurry consolidated kaolinite specimens, which are known to be encountered in recent alluvial marine sediments. Methods are described to evaluate the magnitudes of these physico-chemical components and their incorporation in true effective stress. Results of the study demonstrate that differential osmotic stress finitely contributes to true effective stress. The contribution from differential osmotic stress enables kaolinite specimens to sustain larger void ratio during consolidation. [ABSTRACT FROM AUTHOR]

Copyright of Irrigation & Drainage is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

When evaluating the range of salt weathering of loess check dams during freeze-thaw, the freezing point and its relationship to suction should be considered. Field surveys on the salinity of loess slopes of check dams in Shenmu county of northern Shaanxi were conducted in spring from 2019 to 2021. Marked salt concentration was observed in the slope surface, approaching the threshold of saline soil of 0.3% and sodium sulfate was the main component. Freezing point, suction and microstructure of sodium sulfate loess after freeze-thaw were studied. Results show that soil freezing point decays with freeze-thaw cycles, which is linked to pore structure and particle morphology, as revealed from quantitative indexes of soil microstructure. The matric suction of sodium sulfate loess declines with freeze-thaw, while the osmotic suction that depends mainly on solute concentration is less correlated. The Mizoguchi model was found to be valid for estimating the freezing point of salt-free loess, but it deviates significantly for sodium sulfate loess. To address the above limitation, a modified model that considers the correlation between soil freezing point and suction under freeze-thaw conditions was suggested and verified by test data. • Marked accumulation of sodium sulfate was noted on the loess check dams. • Matric suction of loess decays with freeze-thaw while osmotic suction is unrelated. • A modified Mizoguchi model considering freeze-thaw effect was established. [ABSTRACT FROM AUTHOR]

The volume change behaviour is usually expressed by different curves of e – p when concentrated pore fluids are introduced to clays. Increase in effective stress from osmotic suction in salt solution and increase in inter-particle attraction from the pore-water salt concentration in salt-clay system. The void ratio is smaller in the salt solution with higher concentration under the same vertical overburden pressure, and it results the different curves of e – p in salt solution with different concentration. This paper aims to express the e – p relationship using a unique curve for clays in salt solution with different concentration. A conceptual model is proposed to explain the influence of osmotic suction on the volume change of clays in a quantitative way. A new formula for effective stress is proposed as p e = p + p π incorporating with osmotic suction ( π ), and p π = ( p / π ) D ‐ 2 π . Experimental data for volume change of clays in NaCl solution with different concentration can be expressed by a unique curve using the proposed effective stress. [ABSTRACT FROM AUTHOR]

Compacted expansive clays swell due to crystalline swelling and osmotic/double layer swelling mechanisms. Crystalline swelling is driven by adsorption of water molecules at clay particle surfaces that occurs at inter-layer separations of 10-22 Å. Diffuse double layer swelling occurs at inter-layer separations >22 Å. The tendency of compacted clay to develop osmotic or double layer swelling reduces with increase in solute concentration in bulk solution. This study examines the consequence of increase in solute concentration in bulk solution on the relative magnitudes of the two swelling modes. The objective is achieved by inundating compacted expansive clay specimens with distilled water and sodium chloride solutions in free-swell oedometer tests and comparing the experimental swell with predictions from Van't Hoff equation. The results of the study indicate that swell potential of compacted expansive clay specimens wetted with relatively saline (0.4, 1 and 4 M sodium chloride) solutions are satisfied by crystalline swelling alone. Comparatively, compacted clay specimens inundated with less saline solutions (0.005-0.1 M sodium chloride) require both crystalline and osmotic swelling to satiate the swell potential. [ABSTRACT FROM AUTHOR]

Tensiometer is one of the most popular and simple instrument for in situ and laboratory measurement of negative pressure or suction in soils. Such measurements in the top soil or root zone are useful for automated optimized irrigation scheduling for different vegetation. The top soil accommodates various salts/contaminants whose main source is storm water runoff, irrigation water and application of crop fertilizers. These salts accumulate in the soil due to evaporation. It is an established fact that tensiometer measures only soil matric suction with the help of a ceramic interface. It is believed that osmotic effect of salts present in the soil does not influence tensiometer measurements. However, there is no systematic experimental verification in the literature to understand the influence of salt laden soil on tensiometer measurements. It needs to be ascertained that the pore size of the tensiometer ceramic will not exhibit semi-permeable membrane characteristics leading to osmotic effect. Such verification is important as it would influence the irrigation scheduling of crops. It is also of interest to know whether the osmotic suction (due to the salts) would increase the water retention characteristics and hence the irrigation requirement. If so, then the tensiometer based irrigation scheduling would be an underestimate of the actual irrigation requirement of crops. To investigate these issues, the present study has performed controlled laboratory suction measurements using tensiometer in a locally available soil, contaminated with known concentration of inorganic salt solution. The total suction of the same salt laden soil has been measured using the WP4 dew point potentiameter technique. The results indicate negligible influence of salts present in the soil on tensiometer measurements. The study demonstrates the incapability of tensiometer to assess the osmotic component of salt present in the soil. This would result in the under prediction of water retention and hence irrigation requirement of the soil. [ABSTRACT FROM AUTHOR]

Estimation of osmotic compression strain magnitudes is important in certain geoenvironmental engineering applications. Typically, clay barriers exposed to chemical concentration gradients in waste disposal facilities are susceptible to osmotic compression strains. The chemical concentration gradient between pore water of clay and external chemical reservoir induces osmotic compression strains. The current laboratory method is based on consolidating the saturated clay specimen to the desired consolidation pressure and replacing the distilled water in the oedometer reservoir with preferred salt solution. As dissipation of osmotic suction difference is diffusion controlled, establishing the time-osmotic compression curve at each consolidation pressure may extend over weeks. Designing oedometer experiments that facilitate rapid estimation of osmotic compression strains forms the focus of this study. A double oedometer test based on an earlier concept of Barbour and Fredlund is developed to rapidly estimate the osmotic compression strains of saturated clays at multiple consolidation pressures. The proposed double oedometer method relies on establishing volumetric strain (e)-log pressure curves of clay samples saturated with distilled water and salt solution respectively and reading the difference in volumetric strains of the two clay samples at constant consolidation pressure. The predicted osmotic compression strains from double oedometer method are compared with experimental osmotic compression strains obtained using single oedometer test. [ABSTRACT FROM AUTHOR]

This paper presents a study on osmotic suction of compacted highly plastic clays. Two different types of bentonite (i.e. Calcigel and a bentonite from India called herein as Indian bentonite) were used. Squeezing technique was utilized to obtain soil pore-water of the specimen. Using relationship between electric conductivity and osmotic pressure of salt solution, osmotic suction of soil pore-water was obtained. Additional tests (i.e. total and matric suction using filter paper method and swelling pressure using constant volume swelling pressure test) were performed. The results show that osmotic pressure of soil pore-water obtained decreases by increasing squeezing pressure. Based on experimental result, osmotic suction of the specimen is osmotic pressure of the first drop of extracted soil pore-water. An empirical method was suggested to determine the squeezing pressure in squeezing technique. In addition, roles of osmotic suction in thermo-hydro-mechanical behavior of highly plastic clays were presented and discussed in the paper. [ABSTRACT FROM AUTHOR]

Abstract: Osmotic suction arises in clay soils due to the presence of dissolved salts in soil water. Variations in dissolved salt concentration of soil water impact the osmotic suction balance between soil water (of clay soil specimens) and external reservoir that gets adjusted through diffusion of salts and osmotic flow of water molecules. Available theoretical and experimental studies in literature mostly focus on the behaviour of clay samples reconstituted from slurries. Compacted clays differ from clay samples reconstituted from slurries as they are characterized by both matric suction and osmotic suction. Compacted clays are typically exposed to osmotic suction gradients in landfills and brine ponds where compacted clay liners are in contact with leachate/brine solutions. Upon exposure to solutions, diffusion of salts dissipate osmotic suction gradients, while, absorption of salt solutions in the partly saturated void spaces dissipate matric suction of the compacted clay specimens. The impact of dissipation of matric suction and osmotic suction gradients on the swelling behaviour of compacted expansive clays forms the focus of the present study. Experimental results illustrated that the direction of salt diffusion during dissipation of osmotic suction difference has a significant bearing on the swelling behaviour of compacted clay specimens. [Copyright &y& Elsevier]

This paper presents suction and strength characteristics for a dense, compacted, unsaturated sand–bentonite mixture under a variety of preparation and stressing conditions. Suctions were determined experimentally using thermocouple psychrometers and the filter paper method. They are shown to be related to water contents, saturation, dry densities and osmotic agents. The influence of the initial suctions on strength was evaluated using quick undrained triaxial compression tests, here called ‘constant-mass’ tests. Examination of the suction response to applied external stresses was carried out using stress-controlled triaxial tests along selected stress paths. These tests measured suctions in tests where the mean stress p and deviator stress q were changed systematically to give a series of constant values of Δq/Δp. The results showed that suction decreased as mean stress loading increased. Suction changes appear to be produced only by the mean stress component of the stress tensor and not by the shear stress component. In this compacted sand–bentonite material, for the pressure range at which the tests were performed (p′≤3 MPa), changes in suction produced by changes in mean stress are largely reversible. [Copyright &y& Elsevier]

The salinization of agricultural soil is a common issue of concern. However, the coupling relationship between soil chemical properties and mechanical behavior has been largely ignored. A constant water content triaxial test was conducted by controlling suction on unsaturated agricultural soils collected from paddy fields. The soil samples were diluted with different salt solutions (a distilled water, a sodium chloride (NaCl) solution and a calcium chloride (CaCl 2) solution) to investigate the influence of salinity on the mechanical behavior of soils. The pore water pressure of silt loam was significantly influenced by the pore water salinity, while the pore water pressure of silty clay was significantly influenced by the net normal stress. The results showed that the salt type and concentration significantly affected the cohesion value of silt loam. An empirical constitutive model that incorporated osmotic suction was presented in this paper to explain and quantify the effect of pore water salinity on the shear strength of silt loam. Osmotic suction was considered an independent stress variable in the constitutive model, unlike the salt type and concentration. The Barcelona unsaturated constitutive model explained how the pore water salinity affected the mechanical behavior of agricultural silt loam. With an increase in the osmotic suction in silt loam, the yield surface expanded to both sides of the original ellipses, resulting in an increase in cohesion. The constitutive framework considering osmotic suction provides an improved prediction of the mechanical behavior of agricultural soil under natural conditions subjected to salinization/desalinization. This framework can be implemented in a stabilization plan when the soil and salt are involved in agricultural activities. • A modified unsaturated triaxial test to obtain detailed mechanical behavior of agricultural soils • Investigated the influence of soil pore water salinity on the mechanical behavior of agricultural soil. • Soil pore water salinity had a higher influence on silt loam than silt clay. • The osmotic suction should be considered as an independent stress variable in the constitutive framework. [ABSTRACT FROM AUTHOR]

In this study, the relationship between freezing point and suction of four types of chloride loess samples (CaCl 2 , MgCl 2 , NaCl and KCl) was investigated by freezing point tests and filter paper method-based suction tests. Break points were observed from the freezing point versus water content curves near the plastic limit, which decline at higher salt contents. The freezing point declines roughly linearly with salt content for samples with 2–1 type chloride salts (CaCl 2 and MgCl 2), while decreases attenuatedly for those with 1–1 type chloride salts (NaCl and KCl). The higher the cation content, the more significant the freezing point depression, and the ranking of Mg2+ > Ca2+ > Na+ > K+ was roughly noted, which is linked with the cation hydration capacity. In addition, the relationship between the osmotic suction of samples h 0soil and that of chloride solution h 00solution was suggested to be described by a linear relationship. The freezing point of samples depends on both matric suction and osmotic suction. The limitations of the Mizoguchi's model were noticed through data analysis and by retaining its basic construct, a suction-based model for freezing point of chloride loess was established and verified. • Relationship between freezing point and suction of chloride loess was revealed. • Effect of cations on freezing point of chloride loess depends on hydration degree. • Osmotic suction of chloride loess is fitted as a function of that of chloride solution. • A modified Mizoguchi model for chloride loess considers the influence of suction. [ABSTRACT FROM AUTHOR]

The chemical composition of pore fluid and matric suction rule the mechanical behaviour of soils. In case of clays, their fabric changes in line with those variables. Since both the increase in matric suction and salinity cause a transition from an open to a close microstructure of low and medium activity clayey materials, a unique framework could tackle problems where salinity and saturation changes are expected. This paper presents a simple elasto-plastic model capable of reproducing the behaviour of unsaturated clayey soils in saline environments. Changes in the pore fluid composition are addressed through the use of osmotic suction as a variable. The proposed model extends the Barcelona Basic Model for partially saturated soils to consider the effect of osmotic suction. The model, implemented in the Thebes code, is calibrated for Boom Clay. The reproduced tests include mechanical loading at different matric and osmotic suctions in oedometric conditions, as well as more complex chemo-mechanical stress paths. Despite the simplicity of the formulation, the agreement between the experimental results and the simulations is encouraging. It seems that the modelling approach addresses the most important features of partially saturated soils with saline pore fluid which are slightly or moderately expansive. • A simple modelling framework for partially saturated clays in saline environments is proposed. • The modelling framework is based on a sound microstructural interpretation. • The Barcelona Basic Model is enhanced to consider the effect of osmotic suction. • The model is applied to reproduce experimental data on compacted Boom Clay. [ABSTRACT FROM AUTHOR]

Investigation of the effect of salt solution on the swelling properties of compacted bentonite is of great importance for evaluation of the properties of behavior of engineering barrier in deep geological repository for disposal of high-level radioactive waste. In the present work, a multitude of swelling deformation tests were performed on sodic bentonite using NaCl, KCl, and CaCl 2 solutions. It is revealed from the results that the swelling strains of the tested samples in variety of saline solutions follow the order of NaCl > KCl > CaCl 2 at the concentration of 0.1 mol/L (M), whereas the order was NaCl > CaCl 2 > KCl at 1.0 M concentration. The fractal e m – p e relations for swelling deformation of Na-bentonite in different solutions were estimated, where e m is the smectite void ratio at saturation, p e is effective stress incorporating osmotic suction depicting the effects of ionic concentration on swelling. In addition, the effect of the cation exchange is described using the smectite swelling coefficient K. The estimation values fit well with the experimental data. In NaCl solutions, the coefficient K is basically unchanged due to the weak cation exchange reaction. On the contrary, Ca2+ can much easily replace Na+ even at low concentrations and the CaCl 2 solution exhibits the highest values of osmotic suction, the swelling coefficient and swelling deformation of the samples in the 0.1 M CaCl 2 solution are smaller than that of samples in other 0.1 M solutions. However, at high concentrations, Na+ can be fully replaced by both Ca2+ and K+. The hydration energy of K+ is comparatively lower due to which the swelling coefficient of the samples in the 1.0 M KCl solution significantly decreased thereby resulting in least swelling deformation. • Effects of different salt solutions on swelling are expressed by e m - p e relation. • Exchangeable cations have little effect on the surface fractal dimension. • Effects of cations on swelling are described by smectite swelling coefficient. [ABSTRACT FROM AUTHOR]

The impact of multi-component hypersaline groundwater is simulated by synthetic hypersaline water with 330 g/L total dissolved solids and an osmotic suction of 41 MPa. The effects of this hypersaline water on the retention behavior of compacted MX80 and MX80/ poorly graded sand mixtures as well as MX80 amounts and distributions of soluble and exchangeable cations, and their valences were investigated. Wetting path unconfined condition total suction measurements on pre-hydrated and compacted specimens were reported for MX80 and MX80/sand mixtures prepared at different dry densities and water contents with deionized and hypersaline water. The hypersaline water had no effect on total suction and soluble cations until about 13% gravimetric water content and then the effect gradually increased up to a gravimetric water content of 18%, at which point the total suction values of MX80 were dominated by the osmotic suction of the pore fluid. For the levels of initial compaction and percentages of MX80 in the mixture studied, there was no clear change in the total suction for MX80 gravimetric water contents greater than about 18%. It is indicated that the effect of hypersaline pore fluid should be considered in designing deep geological repositories in a highly saline environment. [ABSTRACT FROM AUTHOR]