Search

Large volumes of waste tires are generated due to the rapid growth of the transportation industry. An effective method of recycling waste tires is needed. Using rubber from tires to improve problematic soils has become a research topic. In this paper, the dynamic response of rubber fiber-reinforced expansive soil under freeze–thaw cycles is investigated. Dynamic triaxial tests were carried out on rubber fiber-reinforced expansive soil subjected to freeze–thaw cycles. The results showed that with the increase in the number of freeze–thaw cycles, the dynamic stress amplitude and dynamic elastic modulus of rubber fiber-reinforced expansive soils first decrease and then increase, and the damping ratio first increases and then decreases, all of which reach the turning point at the 6th freeze–thaw cycle. The dynamic stress amplitude and dynamic elastic modulus decreased by 59.4% and 52.2%, respectively, while the damping ratio increased by 99.8% at the 6th freeze–thaw cycle. The linear visco-elastic model was employed to describe the hysteretic curve of rubber fiber-reinforced expansive soil. The elastic modulus of the linear elastic element and the viscosity coefficient of the linear viscous element first decrease and then increase with the increase in the number of freeze–thaw cycles; all reach the minimum value at the 6th freeze–thaw cycle. The dynamic stress–dynamic strain curve calculation method is established based on the hyperbolic model and linear visco-elastic model, and the verification shows that the effect is better. The research findings provide guidance for the improvement of expansive soil in seasonally frozen regions. [ABSTRACT FROM AUTHOR]

Enzyme induced carbonate precipitation (EICP) is a new bio-cementation technique that utilizes plant-sourced urease to catalyze urea degradation and reaction with calcium iron, resulting in the formation of calcium carbonate (CaCO3) for soil improvement. EICP has considerable promise for novel and sustainable engineering applications such as soil strengthening, pollutant remediation, and other in situ field applications. In this study, the effect of EICP on the geotechnical characteristics of expansive soil is examined. A series of laboratory tests have been performed with an optimal concentration ratio of 0.75 mol/L. The outcomes of the compaction experiment indicated a slight increment in the dry density of the expansive soil from 15.78 to 16.71 kN/m3.Further, it diminished the optimal moisture content of the soil, decreasing it from 22.3 to 18.5%. The utilization of EICP improves the soil mechanical characteristics, reducing swelling pressure by 80% and increasing the UCS, cohesion, friction angle, unsoaked and soaked CBR by 66%, 44%, 49%, 441%, and 430%, approximately. Additionally, it leads to a significant decrease in soil permeability, approximately 63%. Moreover, SEM and XRD analysis confirmed the presence of CaCO3 content in the treated soil. The experimental findings indicated that the EICP method holds promise in enhancing expansive soil within engineering projects. [ABSTRACT FROM AUTHOR]

MX80 bentonite pellet/powder mixture has been considered as a candidate sealing/filling material in geological high-level radioactive waste disposal. As a single pellet can play an important role in the global hydro-mechanical behaviour of the mixture, the compression behaviour of a single MX80 pellet was investigated by performing uniaxial compression tests on cylinder-shaped pellets at different initial suctions, imposed by the vapour equilibrium technique. Large cracks were observed at suctions ≤ 9 MPa. Results from the compression tests showed that the axial strain εaxial contributed to the contractancy, whereas the lateral strain εlateral contributed to the dilatancy. The uniaxial shear strength σa, max, the crack closure (CC) stress σcc, the crack initiation (CI) stress σci, the crack damage (CD) stress σcd and the Young's modulus E were found to decrease with decreasing suction, providing evidence of the suction effect through softening and cracking. CI was considered as the inflection point of Δεlateral and the onset of dilatancy. Because of the combined effects of suction and wetting-induced cracks, the Poisson's ratios v increased until the suction decreased to 38–25 MPa, and then decreased with further suction decrease. Loading closed the wetting-induced horizontal cracks at suctions ≤ 9 MPa, leading to a drop of εlateral before CC. [ABSTRACT FROM AUTHOR]

Index properties such as liquid limit, plasticity index, shrinkage index, colloidal content, and free swell index (FSI) are used to identify and classify the nature of soil expansivity. However, for these tests either powdered or remoulded soils are used for testing and do not reflect the field placement conditions and soil structure. Hence, the present article proposes a new Desiccated State Free Swell (DSFS) index to encompass the field placement conditions and soil structure. In this method, the small compacted soil specimens are subjected to two-stage process – desiccation followed by swell measurement. The compacted or undisturbed soil specimens are placed in 100 ml glass measuring jars and allowed to swell in distilled water, similar to the FSI test. The percentage increase in the volume of the desiccated soil specimens is measured, and the same is used for the classification of degree of soil expansion. A total of 21 soils covering a wide range of plasticity characteristics and swell potentials were used for the present study. Based on the DSFS test results, a new classification chart is proposed for the prediction of the degree of soil expansion. The experimental findings revealed that the soil expansion predicted using the DSFS method is superior to the conventional indirect methods and matches well with the oedometer swell potentials. [ABSTRACT FROM AUTHOR]

Expansive soils are characterized by significant swelling and shrinkage due to changes in water content, which could threaten the safety of buildings. In this study, an electrochemical treatment method was used to modify bentonite, with subsequent analysis focused on evaluating the alterations in its physical and chemical properties. The electrical resistance between the soil and the electrodes was significantly reduced by injecting a CaCl2 solution, leading to a substantial decrease in voltage loss at the anode. The thickness of the electrical double layer decreased as the Na+ cations adsorbed by smectite particles were exchanged by Ca2+ ions, which significantly decreased the water adsorption and free swelling ratio. The electrochemical treatment method removed more pore water from soil samples than the electroosmotic consolidation method. Furthermore, the results indicated that the injection of a CaCl2 solution could be effective in restraining the swelling potential of bentonite. The most suitable concentration for CaCl2 solution to modify bentonite by electrochemical treatment method might be 1 mol/L, and the injection volume could be 125 mL/L of soil. The results indicated that the electrochemical treatment method could be a promising in situ technique for modifying expansive soil. [ABSTRACT FROM AUTHOR]

With the rapid development of China's mineral industry, the emission of iron tailings sand has increased sharply. At present, the negative storage and landfill are still the main treatment methods, which does not only occupy a large amount of land resources, but also cause serious environmental pollution. Therefore, large-scale consumption of iron tailings sand is imminent. Iron tailings sand is a kind of waste discharged after the 'useful part' of iron ore is selected by grinding, flotation or magnetic separation under a certain condition. Compared with natural fine aggregate, the particle is finer, angular and more solid, which could be widely used in various practical projects. Among them, the regional differences of iron tailings, raw ore composition, grade, particle size and mining beneficiation refining process have a greater impact on the physical and chemical properties. As an inert material, different activation methods could be conducted to improve the activity of iron tailings sand, whereas, the composite activation is the most effective technology. In this paper, the utilization of building materials of iron tailings sand at home and abroad and its application in other fields are reviewed. The influence of concrete prepared by iron tailings sand on mechanical properties and durability is summarized. The key properties of the application in road functional materials are discussed. The application status of iron tailings sand-based bricks is sorted out. The feasibility of using it to prepare geopolymer is evaluated. Its advantages in the preparation of mesoporous molecular sieves and the improvement of expansive soil are discussed. [ABSTRACT FROM AUTHOR]

Soils with a significant proportion of clay or silt tend to have poor geotechnical characteristics (such as volumetric change and low strength) when exposed to varying moisture contents. The chemical stabilizers currently used are costly and have negative effects on the environment. Arkansas, in the United States, is the leading producer of rice in the country. During rice production, ~20% of the harvested grain consists of rice husk (RH). The rice milling process produces ash with a considerable amount of silicate. Research is being conducted to address the environmental concerns associated with its disposal in Arkansas, as there is growing interest in using rice husk ash (RHA) as a stabilizing additive for problematic soils. For RHA to be effective, an activator such as lime may be needed. The present study focuses on investigating the effectiveness of RHA in stabilizing substandard soils, as no prior study has used RHA as a stabilizing agent in the United States. Additionally, the research aims to determine the optimal proportions of RHA, hydrated lime (HL), or a combination of both. The study employs varying percentages of RHA (3%, 6%, and 9%) and HL (1%, 3%, and 5%) in a unary system. In the binary system, 3%, 4%, and 5% of RHA are combined with 1% HL. The study includes a range of routine tests, such as assessments of Atterberg limits, modified proctor compaction, pH levels, California bearing ratio (CBR), unconfined compressive strength (UCS), and free swell (FS). Furthermore, results from scanning electron microscopy (SEM) coupled with X‐ray diffractometer analyses demonstrated significant improvements in UCS and CBR values for the treated soils, indicating enhanced strength and stability. Moreover, the FS test reveals a reduction in swelling characteristics for the stabilized soils. It was found the optimal dosages of RHA and HL were 6% and 3%, respectively. Notably, when RHA and HL were combined, a blend of these two stabilizing agents exhibited the most promising results in terms of improving the swelling. The optimum percentage of the combined stabilizing agents was 4% RHA + 1% HL. The findings of this proof‐of‐concept research hold substantial potential for the construction industry in Arkansas, offering cost‐effective alternatives to conventional soil stabilization methods while promoting the sustainable and environmentally conscious use of RHA. [ABSTRACT FROM AUTHOR]

Expansive soils, known for their significant volume change with variations in moisture content, are widely distributed around the globe. Due to their swelling properties, expansive soils pose significant engineering challenges, especially in rapidly developing countries like China. This study aims to investigate the swelling mechanisms of expansive soils, focusing on the influence of crack characteristics on swelling behavior. The research methodology includes field investigations, laboratory experiments, and theoretical modeling. By comprehensively considering crack rate, dry density, initial moisture content, and overburden load, a nonlinear regression swelling model is proposed in this research. The degree of crack development in expansive soils is quantitatively characterized by the content of filling materials, leading to the establishment of a crack rate model for expansive soils. Swelling tests on expansive soils with different crack contents were conducted. The results show that the swelling rate is negatively correlated with the initial moisture content and positively correlated with dry density and crack rate. Additionally, the larger the crack rate, the more significant the change in the swelling rate. Furthermore, model validation confirms that this nonlinear regression model accurately describes the relationship between swelling rate and influencing factors. It offers a more precise prediction tool for infrastructure design and maintenance in expansive soil areas, advancing geotechnical engineering practices. [ABSTRACT FROM AUTHOR]

Soil shrinkage characteristic curves are used to describe the shrinkage behavior and hydraulic properties of unsaturated soils. To construct soil shrinkage characteristic curves, a high‐data‐density measurement method is needed that relates water content to soil volume changes. We present a fully automated soil shrinkage measurement setup, based on the simplified evaporation method, to characterize the shrinkage behavior of undisturbed natural expansive clay soils. The high data density creates the opportunity to produce soil shrinkage characteristic curves without the need for a mathematical model. The technique allows for resaturation of the samples after drying, enabling differentiation between reversible and irreversible shrinkage. The setup consists of the commercialized HYPROP2 apparatus combined with optical distance sensors to measure the horizontal and vertical dimensions of the samples, yielding data on the sample volume, weight, and soil water suction. The measurement frequency is once per 10 min, and the measurement period is up to 4 weeks, providing a detailed time series of the drying and shrinkage characteristics. The setup can capture the different shrinkage phases and offers the opportunity to relate the soil shrinkage characteristic curve to soil water suction. The measurement data acquisition rate and accuracy enable detailed interpretation of soil water retention curves for nonrigid soils and are shown to be essential for understanding and quantifying the shrinkage potential of several types of deposits. [ABSTRACT FROM AUTHOR]

ABSTRACT Expansive soils are widespread in the world and coincide with areas of high human activity. The main cause of deep instability of expansive soil slopes is due to their softening caused by excavation and seepage. By developing a comprehensive numerical model based on the theory of unsaturated soil, this study examines the characteristics of stress and displacement distribution of expansive soil slopes through hydraulic‐mechanical coupled numerical simulation. This study analyzes the evolution patterns of slopes with excavation unloading and seepage of water storage to reveal the mechanisms of deep‐seated instability of expansive soil slopes. The findings demonstrate that: The instability of expansive soil slopes begins at the foot of the slope and propagates along the interlayer, affecting the entire slope. Excavation leads to the softening of the expansive soil interlayer and the transfer of shear stress. During water storage, the weakening of the soil strength results in slope instability along the weak interlayer slip. Softening of the expansive soil interlayer facilitates the redistribution of shear forces in the slope and alters the distribution law of the plastic zone in the deep layer. Overly slowing down the slope leads to significant excavation unloading, which is detrimental to the slope's stability. [ABSTRACT FROM AUTHOR]

The risk posed by expansive soils can be lessened by placing foundations at a more deep level below the surface. Structures are able to withstand uplift forces because overburden pressure partially suppresses swelling pressure. In order to transfer the forces to a sufficiently deep depth, this study suggests introducing shafts of a low-expansion overburden material. Soil improved with cement is chosen for this purpose. This study suggests using sand with added excavated natural clay and cement. The expansive clay is added to sand in ratios of 10, 20, 30, 40 and 60%. The clay–sand mixture is then enhanced by cement of 1, 2, 4 and 8% by the weight of the mixture under four curing periods of 1, 7, 28, and 90 days. This material is recommended for use under lean concrete to transfer the loads to lower levels below the foundation depth. The thickness of this material depends on the stresses exerted, the type and the properties of the subsurface soils. The cement-enhanced clay–sand shaft's properties are examined in this work with regard to the swelling potential, compressibility, and the unconfined compressive strength for different clay contents and curing conditions. Stiff shafts were formed and found to support stresses from 600 to 3500 kPa at cement additions in the range of 1% to 8%. Clay content above 30% is found to be not suitable for Al-Qatif clay due to the compressibility and low strength of the mixture. When two percent or more of cement is added, the swelling potential is significantly reduced. This is reliant on the pozzolanic interactions of soils and cement as well as the clay mineralogy. Determining how cement affects clay–sand combinations in regions with expansive soils would facilitate the introduction of a novel, inexpensive technology to support loads applied by the superstructure. [ABSTRACT FROM AUTHOR]

The swelling soils, also known as expansive soils, increase in volume due to an increase in moisture content. The settlement of expansive soils could be the main reason for considerable damage to roads, highways, structures, irrigation channel covers, and the protective shell of tunnels that use bentonite for wall stability. Therefore, it is important to determine the amount of swelling pressure in expansive soils. This research uses two laboratory swelling test methods with constant volume (CVS) and ASTM-4546-96 standard, the swelling pressure of lime-stabilized bentonite soil has been estimated. Based on the key findings of this study, the swelling pressure values of pure bentonite samples tested using the ASTM-4546-96 method, compared to the constant volume swelling test, show an approximately 170% increase. [ABSTRACT FROM AUTHOR]

Objective: To explore the mechanical properties of weak expansive soil under different moisture contents and confining pressures. Methods: The triaxial remolded soil samples with different moisture contents (14%, 16%, 18%, and 20%) were prepared for the obtained Nanyang weak expansive soil. Four groups of 16 consolidated drained triaxial shear tests with a confining pressure of 50, 100, 200, and 300 kPa were carried out to study the effects of confining pressure and water content on the deviatoric stress and pore pressure of weak expansive soil with strain. Results: The study showed that the shear strength of weak expansive soil samples gradually increased with the increase of the water content, but its increase nonlinearly decreased as the confining pressure increased. When the axial strain was small, the pore pressure significantly increased, and the pore pressure increased tended to be stable slowly and gradually as the axial strain gradually increased. Therefore, the research results could be used to avoid the diseases caused by the characteristics of weak expansive soil in engineering construction and provide theoretical references for improving engineering foundations in weak expansive soil areas. [ABSTRACT FROM AUTHOR]

The stability of side walls in terraced fields constructed within expansive soil regions represents a critical challenge, often leading to structural failure due to the unique wetting–swelling behavior of the soil. This study employs a comprehensive approach, integrating analytical and numerical methods to elucidate the mechanism of overturning failure attributed to the swelling effect of expansive soil under conditions of layer‐by‐layer saturation. Initially, the earth pressure acting on side walls, constructed from fiber ecological bags, is assessed in their natural, unsaturated state using Bishop's formula for unsaturated shear strength. The study further explores the failure mode through one‐dimensional analytical analysis, focusing on the horizontal and unrestrained expansion of expansive soil during progressive saturation. Subsequently, the deformation of the side wall and the swelling effect of the soil are numerically evaluated. This is achieved by analogizing the wetting–swelling deformation field in expansive soil to an equivalent temperature field, thereby facilitating the use of finite element numerical simulation to investigate the overturning failure mechanism. Findings indicate that in the natural unsaturated state, the side walls remain stable under no earth pressure. However, as saturation depth attains a critical depth of 1.4 m during layer‐by‐layer saturation, the upper wall rotates outward in the form of local overturning failure, and the corresponding infiltration saturation depth is the critical depth for the local instability of the side wall. The investigation identifies the wetting–swelling effect as the predominant factor leading to the structural failure of side walls in terraced fields situated in expansive soil areas. Moreover, a critical infiltration saturation depth of 2.6 m is determined, beyond which the stability of the side walls is compromised. This research contributes significantly to the understanding of the failure mechanisms affecting terraced agricultural infrastructures in expansive soil regions, offering a theoretical foundation for the development of more resilient construction strategies. [ABSTRACT FROM AUTHOR]

For the expansion soil slope in the JiangHuai area before the disposal of the neglect of expansion of the weak defects and slope disposal after the poor long-term stability of the current situation. This study investigates the ability of ecological slope protection technology to cope with the destabilizing geohazard of expansive soil slopes. Analyzing the collapse reasons of weak expansive soil slopes in the JiangHuai region based on the reinforcement project of expansive soil slopes along highways in the JiangHuai region, combined with actual engineering research, a "storage-resistance" water regulation ecological prevention and control technology is proposed. The feasibility and sustainability of the ecological slope protection technology is discussed in terms of its principles and influencing factors, and the protection effect is verified by combining numerical simulation and field test methods. Research findings suggest that the "storage-resistance" technology effectively prevents rainwater infiltration, particularly under light rain conditions, with continuous blocking capability. Under rainstorm conditions, it can prevent infiltration for about 4 h, significantly enhancing slope stability. Slope rate variations show no significant impact on reinforced slope stability, with maximum deformation occurring at the slope's foot after rainfall. Reinforcement plans should prioritize strengthening support at the slope's base. Proper selection and optimization of technical parameters can lead to more economical and sustainable solutions while extending protection time. Field trials confirm the suitability of the "storage and blocking" water regulation ecological control technology for the JiangHuai region, particularly where light rain prevails. These findings suggest that ecological control techniques for expansive soil slopes can effectively regulate slope moisture changes and reduce the geohazard risk of expansive soil slope instability. [ABSTRACT FROM AUTHOR]

Freeze-thaw effects can significantly alter the volume of expansive soil due to the water-phase change and soil expansion. The montmorillonite content was an important factor influencing the expansibility of expansive soil. This paper investigated the micropore structure characteristics of expansive soil under freeze-thaw cycles with various montmorillonite contents. In addition, the micropore evolution of expansive soils and relationship between the unfrozen water content and temperature were also examined via X-ray diffraction (XRD) and nuclear magnetic resonance (NMR). The results indicated that: (1) the montmorillonite content affected the pore size distribution of expansive soil, and with increasing montmorillonite content, the relaxation time (T2) distribution curves changed from single-peak into double-peaks; (2) after multiple freeze-thaw cycles, the macropores in expansive soil increased and mesopore pores decreased; (3) considering the freezing point and capillary adsorption, the soil freezing characteristic curve (SFCC) could be divided into four stages, namely, unfrozen water, free water, freezing-capillary water, freezing-hydroscopic water; (4) the montmorillonite content only affected the unfrozen water content from 0°C to −5°C, while at temperatures lower than −5°C, the effect of the montmorillonite content on the unfrozen water content was negligible. [ABSTRACT FROM AUTHOR]

Construction resting on soil and rocks containing montmorillonite (MMT) are prone to damage induced by swelling, which involves a significant release of energy. It is often desirable to enhance these soils to mitigate swelling potential, regulate volume changes, and manage energy release. Experimental findings suggest that increasing temperature is one method to improve these soils, with water content, initial volume, and boundary conditions also influencing the swelling mechanism. This study utilizes ab initio molecular dynamics calculations to explore changes in volume and energy within MMT unit cells at the nanoscale due to temperature variations. The response of unit cells of MMT with varying dimensions and quantities of water molecules to temperature is assessed under constrained and unconstrained conditions. Results indicate that the volume changes and energy release of unit cells in response to temperature are contingent upon the presence of water molecules. In unit cells containing water molecules, both energy and volume decrease with rising temperature, whereas in unit cells devoid of water molecules, energy decreases while volume increases as temperature rises. Given the inherent association of soils with water in natural settings, it can be deduced that increasing temperature presents a viable method for enhancing naturally occurring MMT-dominated soils. Density functional theory calculations demonstrate that alterations in the volume and energy of MMT stem from shifts in interactions among the minerals, cations, and water molecules, as well as intrinsic structural defects like isomorphic substitution and peroxy links within the unit cells. These modifications induce variations in charge carriers and electrical properties, consequently influencing volume and energy changes within MMT unit cells. Additionally, it was observed that the failure of peroxy links can significantly impact the optimal temperature selection for the thermal enhancement of MMT. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Architecture & Civil Engineering is the property of Chang'an Daxue Zazhishe 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.)

Sulfate-bearing soils is widely distributed around the world, and this type of soil is prone to rock and soil disasters such as dissolution, corrosion of foundations, and swell when exposed to water. Cement is a frequently used stabilizer to treat sulfate-bearing soils. However, sulfate-bearing soils usually include various types of sulfates, such as, calcium sulfate (CaSO4), sodium sulfate (Na2SO4), potassium sulfate (K2SO4), and magnesium sulfate (MgSO4). So far, the effect of sulfate type on the strength and swelling properties of sulfate-bearing soil stabilized with cement has not been clarified. Therefore, in this study, the strength and swelling properties of four sulfate-bearing soils treated with cement were studied using unconfined compressive strength tests, and swelling tests. X-ray diffraction (XRD), scanning electron microscopy, and inductively coupled plasma spectroscopy were employed to study mineralogical, micro-structural properties, and concentrations of calcium ion of stabilized soils, to explore stabilization mechanisms. The results showed that the formation of magnesium silicate hydrate and highest concentration of free Ca2+ in the stabilized Mg-sulfate-soil caused its lowest strength. The reduction in free Ca2+ concentration was greater in the stabilized Na-sulfate-soil and K-sulfate-soil compared to stabilized Mg-sulfate-soil and Ca-sulfate-soil, contributing to the formation of more calcium silicate hydrate and ettringite. Therefore, the stabilized Na-sulfate-soil and K-sulfate-soil had greater swelling and strength compared to other soils. As the cement content increases, there are abundant in the sulfated cement stabilized soil observed in XRD and SEM photos. Overall, sulfates with monovalent cations increased the strength of cement-stabilized soils more than those with divalent cations, while sulfates with divalent cations improved the resistance to swelling of cement-stabilized soils. Before treating sulfate-bearing soils with cement, it is necessary to first determine the cations type in the soil. If the soil contains Mg2+, seek cement alternatives. If the other three cations are present, choose an appropriate cement content for stabilization. This study provides some references for the stabilization of sulfate-bearing soils with cement. [ABSTRACT FROM AUTHOR]

Highly susceptible to moisture changes, expansive soils are widely recognized as problematic soils. Swelling-induced damages to overlying engineering structures result in financial loss and billions of dollars in repair costs annually worldwide. Therefore, to mitigate swelling potential, various soil amendment approaches have been investigated to date. Sustainable soil treatment techniques such as microbially induced carbonate precipitation, although enjoying a low CO2 footprint, suffer from challenges pertinent to the use of living microorganisms at field scale treatments. Hence, the current study aims to explore the feasibility and efficiency of using enzyme-induced calcium carbonate precipitation (EICP) as an alternative eco-friendly method, yet to be examined for improving swelling characteristics of clayey soil. For this purpose, a series of laboratory experiments from macro- to microstructural scales involving free swell tests, swell pressure, pH measurement, X-ray powder diffraction, Bernard calcimeter, confocal Raman spectroscopy, and scanning electron microscopy have been conducted on the EICP-treated expansive samples. The experimental program focuses on the influence of constituent concentrations used in the EICP treatment on the swelling potential to obtain the optimal EICP solution. The study reveals that EICP can result in more than 60% reduction in the free swell index compared to untreated soil conditions. The results indicate that the EICP technique can double calcium carbonate content within expansive soil, increasing it by as much as 220%. Finally, it is demonstrated that there is a strong correlation between the amount of precipitated calcite and enhancement in the free swell index. [ABSTRACT FROM AUTHOR]

Copyright of Railway Construction Technology is the property of Railway Construction Technology Editorial Office 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.)

This study evaluates the impact of compaction on the soil–water characteristic curve of unsaturated remodeled weakly expansive soils by assessing changes in soil pore structure resulting from variations in compaction. The remodeled weakly expansive soil in the Xinjiang Hami area is taken as the research subject to investigate how compaction affects microscopic pore structure using mercury intrusion testing. Subsequently, mercury intrusion porosimetry is employed to examine pore structure and distribution patterns at different dry densities. Based on the capillary principle and experimental methods (filter paper method and pressure plate method test), modified soil–water characteristic curves are obtained by fitting them with a three-parameter model law. The results indicate that higher dry density leads to an increased air intake value and significantly reduces the total volume of large pores within samples. Both the Fredlund and Xing model and the three-parameter model effectively capture the influence of initial dry density on the development pattern of the soil–water characteristic curve. [ABSTRACT FROM AUTHOR]

High concentrations of sodium chloride dominate oilfield produced waters (brine) of the Williston Basin. When accidental spills of produced waters occur, there is an immediate need to reduce concentrations of chloride, to protect surface and groundwater systems and to reduce concentrations of sodium (Na) in soil to prevent any unwanted swelling and dispersion in soil. Swelling and dispersion of soils will likely occur if sodium adsorption ratio values are too high and the electrical conductivity drops below a certain threshold that is required to maintain flocculation. To prevent this, a calcium (Ca) amendment can be applied to replace Na with Ca on soil exchange sites. Historically, gypsum has been the most common Ca amendment used for improving brine impacted soils. Flue gas desulfurization gypsum is available in North Dakota but is still a sparingly soluble amendment. The purpose of this research was to investigate the use of calcium acetate (Ca‐Ac) as an amendment for brine‐impacted soils as compared to gypsum. Ca‐Ac has a similar concentration of Ca compared to gypsum but is over 100 times more soluble than gypsum. This laboratory experiment will compare how varying levels of gypsum and Ca‐Ac can influence soil hydraulic conductivity, and chemical and physical properties when mixed with oilfield brine‐impacted soils. Core Ideas: Calcium acetate can be a more effective amendment than gypsum to increase water flow in brine‐impacted soils.Clay mineralogy may impact the choice of amendment for brine‐affected soils.The surface area of gypsum impacts the movement of water and also the removal of sodium from soil. [ABSTRACT FROM AUTHOR]

Accurate assessment of pile group's performance in spatially variable unsaturated expansive soil has long been a challenge in geotechnical engineering. This paper presents a methodology to perform reliability analysis for vertically loaded pile group, where the modified load transfer method (LTM) is utilised to investigate the load–displacement response considering the pile–pile interaction and the non-linear relationship of the pile–soil interface under the influence of matric suction reduction and the swelling of expansive soil; the Karhunen–Loève (KL) expansion method is adopted to simulate the spatial variability of soil parameters; the first–order reliability method (FORM) is utilised to perform reliability analysis of each pile in the pile group; and the reliability analysis of pile group is then performed using the sequential compounding method (SCM) by considering the pile group as a parallel system. By applying the proposed methodology to a 3 × 3 pile group under different vertical loads and infiltration times, the relative magnitudes of reliability indices for different piles in the pile group and the pile group system under two failure modes of uplifting and sinking are identified. The effects of soil's spatial variability and pile spacing on the reliability of pile group are also analysed. [ABSTRACT FROM AUTHOR]

The study investigated the reinforcing effect of vetiver root on soil by conducting outdoor planting tests and indoor root tests. The cracking indexes of soil specimens with varying root contents were analyzed, and a statistical model was established to determine the relationship between the cracking indexes, the number of dry and wet cycles, and the root content. The study revealed the crack evolution law of vetiver-reinforced expansive soil. The study explored the mechanism of the vegetation root in inhibiting the cracking of expansive soil and determined the optimal planting density of vetiver grass through outdoor planting tests. The results indicate that: The surface crack rate (CR), total crack length (CL), and crack number (CN) in the root-soil specimen exhibited exponential growth with an increase in the number of wet and dry cycles. This growth was more pronounced during the first and second cycles. The vetiver root could effectively reduce soil crack formation, and the specimen's cracking resistance is positively correlated with the root content. With the root content increased, the CR, CN, and CL decreased. The logistic model is suited to the CL of added root soil. The logistic model is more suitable for the growth model of the CR of the expansive soil with low root content, while the Boltzmann model is more suitable for the growth model of the CR of the expansive soil with high root content. Width of crack (CW) is better suited to the DoseResp growth model. The Boltzmann model is more applicable to the CN in expansive soils with low reinforcement, while the logistic growth model is more suitable for the development of CN above 0.21% root content. The development of the crack network was influenced by two key factors: the root content and the number of wet and dry cycles. Under the condition of planting roots, the development of crack networks in expansive soil differs from that of expansive soil with added roots, and there is no clear pattern to follow. The inhibitory effect of the vetiver root on cracking of expansive soil is related to the planting density of vetiver. [ABSTRACT FROM AUTHOR]

Expansive soils pose significant challenges in civil engineering due to their susceptibility to volumetric changes, leading to structural instability and damage in infrastructure. This study evaluates the performance and microstructural characteristics of industrial solid waste materials (Class F‐fly ash and ground granulated blast‐furnace slag) as additives for stabilizing expansive soils. Tests, including moisture density, unconfined compressive strength, Atterberg limits, compressibility index (Cc), cation exchange capacity, direct shear test, and California bearing ratio, were conducted on the treated expansive soil. Scanning electron microscopy and energy dispersive X‐ray spectroscopy (EDX) were used to analyze the changes in the soil matrix due to the incorporation of the waste materials. The results demonstrate improved engineering properties of expansive soil treated with these additives. The analysis confirms enhancements in particle arrangement, reduced porosity/pore sizes, and improved bonding between soil particles, indicating the formation of calcium silicate hydrate and calcium aluminate hydrate. This research suggests that these waste materials can be eco‐friendly and cost‐effective alternatives for stabilizing expansive soils in construction projects. [ABSTRACT FROM AUTHOR]

The stabilization/solidification method can improve the engineering properties and reduce the environmental risks of heavy metal-contaminated expansive soil. However, the solidification effects deteriorate for soils experiencing wetting–drying (W–D) cycles. For this objective, the expansion/shrinkage, cracking, and leaching behaviors, as well as the corresponding internal relations, of lime-solidified lead-contaminated expansive soil were investigated. The results showed that during the W–D process, the volumetric strain increased, particularly along the radial direction. The cracks gradually developed and increased in length, width, and surface-crack ratio. Contaminant leaching and mobility increased, increasing environmental risk. In addition, a higher Pb(II) concentration in the solidified soil exhibited a more notable expansion potential release, crack development, and leaching capacity. X-ray diffraction and scanning electron microscopy results revealed the redistribution of soil particles and pores rather than chemical changes in mineral components during the deterioration process, and increasing the lead concentration accelerated the deterioration of W–D cycles. Finally, based on the grey correlation analysis, deterioration effects in leaching behaviors were controlled by expansion/shrinkage exponential release for solidified soil experiencing lower W–D cycles and higher Pb(II) concentrations, whereas leaching behaviors were controlled by crack behavior for solidified soil experiencing higher W–D cycles and lower Pb(II) concentrations. [ABSTRACT FROM AUTHOR]

Anchor reinforced vegetation system (ARVS) comprises high performance turf reinforcement mats (HPTRM), vegetation and anchors. It is a new attempt to apply the system in expansive soil slope protection. The goal of this paper was to evaluate the effectiveness of ARVS in protecting newly excavated expansive soil slopes. The field tests on the bare slope, grassed slope and ARVS protective slope were carried out, including natural and artificial rainfall. During the test, the soil water content, soil deformation, and anchor axial force were monitored, and then the slope protection mechanism of ARVS was analyzed. It was found that ARVS can effectively protect expansive soil slopes compared with bare slopes and grassed slopes. The vegetation and HPTRM form a reinforced turf, and the anchors fix it to the slope surface, thus restraining the expansion deformation. The axial force on the anchor of ARVS includes frictional resistance and tensile force transmitted by HPTRM, which is maximum at the early stage of support. The neutral point of the anchor of ARVS moves deeper under atmospheric action, but the vegetation and HPTRM on the slope surface can limit this movement. [ABSTRACT FROM AUTHOR]

Karal soils mainly composed of swelling clays are considered as one of the main causes of degradation in civil engineering structures in Cameroon. Thus, a better knowledge on Karal-type soil behavior is required to adapt soil treatment for road construction and foundation dimensioning. The physicochemical, mineralogical and geotechnical characterization of ten soils collected in North and Far North Cameroon allowed to classify Karal among plastic soils. As expected, the optimum water contents and maximum dry densities of dynamically compacted Karal reflected the particle size distribution and the mineralogical soil composition with various amounts of swelling clay (montmorillonite) and quartz associated to sand and silt fractions. Then the swelling/shrinkage properties of compacted specimens evaluated by free swelling test and volume shrinkage test were correlated to soil characteristics to propose a suitable classification for Karal-type soils. Not only swelling but also shrinkage properties were assessed and combined to define a new parameter called the total amplitude of swelling and shrinkage deformation, allowing the exclusion of the soil initial water content when evaluating soil deformation. After comparison of usual indirect methods to classify swelling soils, a predictive method of clay-rich soils deformation under moisture variation for Karal was proposed and discussed. [ABSTRACT FROM AUTHOR]

During the construction of tunnels in the Chinese Loess Plateau, the primary focus has traditionally been on the loess surrounding the tunnel. However, the swelling of paleosol and the low mechanical strength of loess in thick paleosol strata elevate the risks associated with tunnel construction. The distribution of loess and paleosol significantly influences tunnel stability. In this paper, we monitored the surrounding rock displacement and support structure pressure of a tunnel built within the thick paleosol strata. The thermal–mechanical coupling model was employed to simulate and calculate the swelling of paleosol, and the impact of loess and paleosol distribution on tunnel stability was thoroughly discussed. The results confirm the reliability of the thermal–mechanical coupling numerical model. At the vault and spandrel, where the interface lies between the thick paleosol strata and thick loess strata around the tunnel, the surrounding rock displacement initially increases and then decreases with the decrease in tunnel depth. However, the surrounding rock pressure exhibits an inverse variation, reaching a minimum when the interface is at the bottom of the lower bench. In areas with a thin loess layer around the tunnel, the surrounding rock displacement decreases, while the surrounding rock pressure increases with the reduction in the height of the thin loess layer. Furthermore, in comparison with surrounding rock with a full paleosol section, the displacement safety factor is 0.39–0.40 smaller, but the pressure safety factor is 1.21–1.24 larger when the interface is at the bottom of the lower bench. Simultaneously, the pressure safety factor is 0.17–0.41 larger, but the displacement safety factor is only 0.08–0.09 smaller with the thin loess layer in the upper bench. These findings provide a valuable theoretical reference for the construction of tunnels in thick paleosol strata and multi-strata environments with swelling soil and weak mechanical strength soil. [ABSTRACT FROM AUTHOR]

In this study, a Unified Soil Improvement Technique (USIT) that consists of prewetting, calcium lignosulphonate lime piles, fabric, and soil nail was applied to an expansive soil specimen to both accelerate the process and increase the effect of these techniques. 19 boreholes that had 0.45 cm diameter and 1.9 cm height were opened into an expansive soil specimen in an oedometer ring. Then, these boreholes were filled with a calcium lignosulphonate-water mixture prepared in a liquid form during the prewetting process. Thereafter, these boreholes were filled with a mixture including calcium lignosulphonate, water, and lime. Finally, a fabric was laid down over this specimen and seven pieces of soil nails were used for connecting the fabric and the lime piles. To sum up, the swelling potential of expansive soil specimens under 7 kPa decreased from 43.95 % to 1.58 % after 28 day curing period. The CBR swell of the USIT specimens, which waited in the humid room for 90 days, was measured as 1.14% under 7 kPa surcharge pressure and was measured as 0.4% under 25 kPa surcharge pressure. The significant changes in the swell potential values suggest that the Unified Soil Improvement Technique’s performance is better than calcium lignosulphonate-added lime piles in the improvement of expansive clays. [ABSTRACT FROM AUTHOR]

Expansive soil poses significant challenges for civil engineers, leading to structural damage, particularly in lightly loaded structures. This study employs an innovative and sustainable recipe to stabilize highly expansive soil using the Microbial- Induced Calcium Carbonate Precipitation (MICP) technique by substituting conventional ingredients with olive mill wastewater and hydrated lime. A series of laboratory tests were performed to evaluate the improvement in Atterberg's limits, Free Swell, Unconfined Compressive Strength (UCS), and pH, in addition to a series of qualitative measurements, including X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Optical Microscopic Images, and bacteria growth rate. Different mellowing periods and different cementation concentrations were used. The proposed recipe results showed a 50% reduction in the soil's free swell value. The UCS of the treated soil using the proposed recipe was eight times that of the untreated soil and twice that of the soil treated with the traditional recipe. The SEM images showed flocculation and aggregation in the soil particles, with the voids becoming smaller and filled with calcium carbonate (CaCO3). The XRD results showed the formation of new CaCO3 particles. The optimized recipe demonstrated remarkable enhancement improvement and significant changes in soil physical properties and microstructure. [ABSTRACT FROM AUTHOR]

Investigating crack evolution characteristics in expansive soil under dry–wet cycle conditions is essential for analyzing the shallow instability of embankments and roadbeds filled with this type of soil. Indoor tests on remolded expansive soil specimens were performed under dry–wet cycle conditions, and digital image processing technology (PCAS) was used to quantitatively analyze the process of crack evolution. The study examined how initial moisture content, compaction degree, thickness, and expansibility affect crack development in expansive soil. Additionally, the study discussed the mechanism of crack evolution, considering the characteristics of crack structures in expansive soil. The findings suggest that crack development in expansive soil specimens is influenced by various factors including initial moisture content, compaction degree, thickness, and expansibility. The crack ratio increases with the initial moisture content, thickness, and expansibility, but decreases with the compaction degree. Furthermore, a significant linear relationship exists between the attenuation rate of soil strength and the crack ratio. The development of cracks is governed by the variance in soil shrinkage, which leads to the formation of distinct shrinkage centers at various locations and is markedly influenced by the soil's thickness. This research explores the laws governing the evolution of cracks in expansive soils, elucidating the mechanisms by which these cracks evolve under the influence of various factors. It addresses a significant gap in the theoretical understanding of crack evolution in expansive soils under conditions of multiple influences, thereby offering crucial insights into the characteristics of soil evolution. [ABSTRACT FROM AUTHOR]

Expansive soils poses significant challenges in civil engineering projects, yet construction on them in many circumstances is unavoidable. Soil modification, therefore, is one of the finest options for improving the expansive properties of such soils. This study uses commercially available Sodium Bentonite as an expansive soil, where Recycled Glass Powder (RGP) alone and in combination with Polypropylene Fiber (PPF) are used as modifiers. RGP in the percentages of 5%, 10%, 20%, and 30% by dry weight, and 20% RGP in combination with PPF in the proportions of 0.25%, 0.5%, and 1.0% by dry weight of the soil sample were used in the study. Various tests to evaluate the index and engineering properties of both virgin and modified soil samples were carried out, including Atterberg limits, linear shrinkage (LS), specific gravity, compaction, free swelling index (FSI), expansivity index (EI), and one-dimensional consolidation test. Moreover, scanning electron microscopy and zeta-potential test were carried out to analyze the microstructural and electrokinetic properties of modified soil. The results demonstrated a significant decrease in LS (35.43%), FSI (62.23%), EI (50.29%), swelling index (37%), and compression index (22%) with the addition of 30% RGP. Furthermore, incorporating 1% and 0.5% PPF showed a remarkable decrease in LS (50%), and EI (31.78%), respectively as compared to the base soil mix with 20% RGP. Overall, recycled glass powder (RGP) and polypropylene fiber (PPF) as modifying agents hold strong potential for enhancing the expansive and swelling properties of highly expansive bentonite clay, offering promising solutions for construction challenges associated with expansive soils. [ABSTRACT FROM AUTHOR]

The aim of this study is to analyze the stabilization effects of an expansive soil using three different nontraditional chemical additives, in this case: white cement and nano-silica as admixture, waste granite dust, and a new liquid polymer soil stabilizer (i.e. liquid granite). The engineering properties such as soil consistency, linear shrinkage and soil swelling behaviour of a bentonite treated with these stabilizing agents were investigated. Furthermore, the bearing capacity of the stabilized bentonite was analyzed through the California Bearing Ratio test (BCR) and a laboratory foundation model. The experimental program consisted of three series of tests. In the first series, the tests were performed on an expansive soil reinforced with 2%, 4%, 8%, and 10% of white cement combined with 2% of nano-silica. Another series of tests consisted of samples mixed with different percentages of granite powder (5%, 10%, 15%, and 20%). In the third series, liquid granite as a soil stabilizer was blended with soil specimens at various concentrations (1%, 2%, 3%, and 4%). For all admixtures, the results showed a marked improvement in soil consistency, an important decrease in linear shrinkage, a considerable reduction on the expansion index, and a significant improvement of CBR and soil bearing capacity. Moreover, two empirical correlations were proposed between the bearing capacity parameters (i.e. CBR and Improvement factor) and the expansion index. [ABSTRACT FROM AUTHOR]

Most biopolymers used as additives for the improvement of expansive subgrade soils are ecofriendly but highly uneconomical and unsustainable. Even the traditional additives such as cement, lime, and fly ash that are used widely for most soil improvement schemes are highly notorious for their carbon footprint. This necessitated the motivation in the present study to utilize an economical, ecofriendly and highly sustainable biopolymer, known as pregelatinized corn starch (PGCS), to improve the strength properties of an expansive subgrade soil. The PGCS was admixed with quarry dust (QD), an industrial waste additive, before blending with the expansive subgrade soil in different mix ratios generated with a 32 full factorial design experiment. The California bearing ratio (CBR) samples were subjected to 7 day curing while that of the unconfined compressive strength (UCS) were subjected to 1, 7, and 28 day curing. Shortly after the improvement of the expansive subgrade soil, the PGCS and QD were used as predictors in the development of two regression models for the two strength parameters (CBR and UCS) of the expansive subgrade soil considered in the study. Next, multiobjective salp swarm optimization algorithm (MOSSA), a bioinspired algorithm, was employed to optimize the additives in order to obtain optimal values of the strength properties of the expansive subgrade soil blended with the additives. The developed models were set as fitness functions in the slightly modified MOSSA technique. Thereafter, nondominated solutions were determined after the implementation of the optimization analysis. The results obtained from laboratory experiments and the optimization process showed that there was significant improvement in the UCS and CBR of the expansive subgrade soil. Optimal improvement in the UCS (1,326.241 kN/m2) and CBR (36.8%) were observed when an optimum mix ratio of the additives, 0.3117% PGCS and 10% QD, was blended with the expansive subgrade soil. [ABSTRACT FROM AUTHOR]

Expansive soils present substantial challenges in civil engineering because they undergo volume fluctuations with changes in water content, mainly affected by the clay mineral montmorillonite. Nanotechnology has rapidly and widely improved, finding applications across all engineering fields. This study focused on enhancing soil engineering performance using lime alone and the impact of varying quantities of nanosilica with lime in the soil, focusing on engineering parameters like Atterberg limits, maximum dry density, optimum moisture content, and unconfined compressive strength over curing periods of 7, 14, and 28 days. In this study, the basic properties of soil were initially determined. Then, lime was mixed with soil in different proportions of 2%, 4%, 6%, and 8% according to the dry weight of the soil. Based on strength criteria, soil mixed with 4% lime gives the best results. Keeping the lime content constant at 4%, nanosilica was added to the soil. These findings suggest modifications in the amended soil's plasticity, compaction characteristics, and strength with the minor addition of nanosilica to lime-mixed black cotton soil. The enhancement in strength of expansive soils relies on the amount of lime and nanosilica and the duration of curing. After conducting tests, it was found that the optimal quantities for lime and nanosilica through strength performance tests are 4% and 3%, respectively. The research asserts that adding nanosilica to lime notably improves the mechanical properties of black cotton soil. Scanning electron microscopy and X-ray diffractometer analyses support these findings, revealing variations in the character and strength of the CSH phase over curing time. These conclusions offer wide-ranging relevance for projects seeking to enhance the engineering properties of soft soils. Practical Applications: Soil with 4% lime and 3% nanosilica gives good results, and the use of lime in soil stabilization contributes to the reduction of environmental pollution. The cost of nanosilica for real projects demands huge quantities. From an economic and commercial perspective, nanosilica liquid and lime are generally considered cost-effective for most practical applications. However, nanosilica with lime is recommended in areas where durability is important. Lime with soil is used to strengthen the soil in pavements and embankments; for example, when strengthening black cotton soil used for an embankment with a top width of 2 m, height of 6 m, side slope of 1:1, and length of 1 m, the volume is calculated as 48 m³. For soil +4% lime +3% nanosilica, the dry density is 17.1 kN/m³ and the moisture content is 14.9%. Considering this, the mass of the sample is obtained as 943 kN. Consequently, the required quantities are 38 kN (3,872 kg) lime, 28 kN (2,435 L) nanosilica liquid, and 877 kN (89,443 kg) of soil in its dry state. The cost of lime and nanosilica liquid depends on the location. [ABSTRACT FROM AUTHOR]

This research mainly sought to evaluate the sediments of the Urmia lake bed to prevent their erosion and the possibility of improving the problematic saline fine soils in the region by the geo-polymerisation process. For this purpose, perlite and pumice materials, with pozzolanic properties and weight percentages of 3, 5, and 7, were separately mixed with soil, along with the calcium hydroxide (Ca(OH)2) solution as a catalyst with 2%, 5%, and 7%. Then, the samples were cured for one day. Uniaxial compressive strength (UCS), direct shear, and consolidation tests were performed to assess the geotechnical properties of improved soil compaction. The results revealed that, compared to pumice, perlite could improve the behavioural properties of the studied soil. The inclusion of perlite and pumice, along with calcium hydroxide, increased the flexibility of the stabilised soil, as indicated by the brittleness index. Similarly, combining 3% perlite with 2% Ca(OH)2 could increase UCS at failure by 3.27 times. In addition, the mixture of 5% perlite with 7% Ca(OH)2 could enhance the shear strength by 3.3 times. Finally, combining 3% perlite with 5% calcium hydroxide reduced the swelling of the improved soil by 82%, and the consolidation settlement was decreased by 64% on average. Highlights: Sodium saline silty soil can cause many problems, such as settlement and swelling in ground and underground structures. The present research investigated the effects of perlite and pumice materials and calcium hydroxide as a catalyst on improving saline silty soil. The results revealed that perlite is more effective than pumice because of its pozzolanic properties. As a result of mixing perlite with saline silty soil along with calcium hydroxide, after curing, the skeleton of the soil particles changed from fine to coarse grains, modifying the characteristics of the soil. [ABSTRACT FROM AUTHOR]

A study was conducted on the effects of temperature and salt concentration of pore fluid on the properties of an expansive soil during drying and wetting cycles. The experimental tests were performed on modified and conventional odometers at constant and variable temperatures under 10 kPa surcharge pressure. Distilled water and solutions of sodium chloride and calcium chloride with concentration of 250 g/litre were used for making samples and distilled water was used for inundating samples during the wetting stage. The results showed that the swelling potential is decreased with increasing the number of cycles for both constant and variable temperature conditions. It was revealed that the potential of swelling is a function of salt concentration of pore fluid of the sample and the effect of temperature on the potential of shrinkage and swelling is negligible. The variation of void ratio with water content is dependent on the salt concentration of pore fluid and the position of void ratio-water content curve is a function of temperature. The results of scanning electron microscopy (SEM) tests showed that the structure of soil is changed during drying and wetting cycles which results in the reduction of potential of shrinkage and swelling. [ABSTRACT FROM AUTHOR]

This paper reports the average pore water density (ρwp) measured on a Japanese bentonite, which was compacted to a dry density (ρd) range from 0·3 to 1·8 Mg/m3 and saturated under a water pressure of 2·7 MPa. It was found that ρwp monotonically increased from ∼1·0 Mg/m3 at ρd of 0·3 Mg/m3 to ∼1·23 Mg/m3 at ρd of 1·8 Mg/m3. A review of the available literature revealed that the methodology of accurately measuring ρwp in a full range of water content (w) is not available. An upper boundary of ρwp for montmorillonite was drawn, and proportions of water at different swelling states were estimated. [ABSTRACT FROM AUTHOR]