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We conducted an experimental study on the swelling–shrinking characteristic of expansive soil treated with enzyme-induced carbonate precipitation (EICP) using yellow soybean. A series of tests including the free swell test, swelling rate test, swelling pressure test, and shrinking test were conducted on expansive soil specimens with various water contents and equimolar concentrations. The test results showed that EICP-treated expansive soil samples exhibited an obvious reduction in the magnitude of free swelling rate, swelling rate, swelling pressure, and shirking rate compared with the untreated one. This indicates that EICP using yellow soybean can effectively reduce the swell and shrink potential of expansive soil. The free swelling rate consistently decreases with the increasing equimolar concentration. A more remarkable reduction in swelling rate can be observed at a concentration of 1 mol/L compared with a less significant decrease at a higher concentration. The free swelling rate shows an ascending trend first and then a declining tendency with the increase of water content at higher equimolar concentrations. The influences of equimolar concentration and water content on the change of swelling rate for treated samples with applied loading pressures are insignificant. The swelling pressure reduces remarkably with increasing equimolar concentration and then tends to level off. The swelling pressure exhibits an ascending tendency with the increase of water content. The shrinking rate reduces more remarkably with equimolar concentration at first and then increases less remarkably, with an equimolar concentration of 2 mol/L exhibiting the lowest shrinking rate. The soil specimen with higher water content shows a higher value of shrinking rate than that with a lower one. [ABSTRACT FROM AUTHOR]

Rain-induced shallow failures in expansive soils often occur on gentle slopes with slope ratios of 1:2–1:6, resulting in highly complex stability issuesThis study established an equivalent theoretical model for the swelling behavior of expansive soils based on the similarity theory of temperature and humidity fields. A numerical simulation approach was developed using a model with consistent nodes and the conversion of seepage results and swelling loads, allowing for the decoupling analysis of slope seepage–deformation–stress considering swelling and strength softening. Numerical analyses were conducted on a specific slope profile in a case study, analyzing the distribution and evolution of the slope seepage, deformation, and shear stress. The findings revealed that changes in moisture content at the slope toe have the most significant impact, with infiltration depth and strength attenuation being the largest. Horizontal and vertical deformations were also highly influenced by the reduction of shear strength. The uneven water absorption and swelling of expansive soil slopes resulted in shear stress concentration areas on the slope, leading to local failures near the slope toe and eventual overall instability of the slope. This study provides valuable insights into the complex behavior of shallow failures in expansive soil slopes. [ABSTRACT FROM AUTHOR]

The shear strength and stiffness characteristics of steel slag indicate that it can potentially be utilized as a competent base/subbase material of bound and unbound pavement layers. However, concerns with respect to the utilization of steel slag remain due to its long-term swelling, corrosivity, and leaching characteristics. In this study, long-term swelling and corrosivity tests were performed on basic-oxygen-furnace steel slag (BOFSS) and electric-arc-furnace ladle steel slag [EAF(L)SS] generated in Indiana, USA. In order to reduce the 1D swelling strains of these slags, 5%, 10%, and 20% Class C fly ash (CCFA) and 10% ground rubber replacement ratios were used to prepare steel slag mixtures for testing. The improvement due to CCFA replacement was evaluated by performing unconfined compression and long-term swelling tests on selected steel slag–CCFA mixtures. The seven-day unconfined compression strengths of 90% EAF(L)SS + 10% CCFA and 90% BOFSS + 10% CCFA mixtures were 2,387 and 3,768 kPa, respectively. After nine months of monitoring, the maximum 1D swelling strains of soaked samples of BOFSS and EAF(L)SS mixtures prepared with 10% CCFA replacement were 0.1% or less. The unconfined compression and swelling test results for the steel slag–CCFA mixtures indicated superior strength gain characteristics and negligible swelling strains with time than for steel slags. [ABSTRACT FROM AUTHOR]

In nature, expansive soil is generally in a state of swelling during rainfall, and its soil–water characteristic curve (SWCC) exhibits a three-dimensional space shape under the action of an increasing void ratio. In this study, expansive soil from Hefei, China, was used. SWCC and hygroscopic tests were performed. A three-dimensional hygroscopic swelling mathematical model of the dry density–void ratio–saturation degree was constructed based on the volume change behavior of expansive soils resulting from the hygroscopic test. In addition, depending on the variation in suction with the saturation degree of expansive soil under different values of dry densities, an SWCC mathematical model considering the swelling effect was constructed. The three-dimensional surface model of the hygroscopic swelling of the expansive soil was steeper in the lower saturation degree area. As the saturation degree increased, the three-dimensional surface gradually became flat. The SWCC model of the expansive soil under the action of swelling in a three-dimensional space is an S-shaped surface. The model exhibited dynamic changes in the suction and saturation degrees as the dry density of the soil decreased continuously. The model comprehensively revealed the hydraulic and swelling properties of expansive soil. [ABSTRACT FROM AUTHOR]

Due to the fast-growing number of cars, the amount of scrap tires is quickly increasing across the world. Because buried tires need a long period of time to dissolve, the accumulation of scrap tires in different countries has caused several social, economic, and environmental issues worldwide. Many researchers in geotechnical engineering have utilized scrap tires in various forms for soil reinforcement in recent years. A by-product of waste tire processing is waste tire textile fiber (WTTF). These WTTFs are classified as special wastes, and they are frequently buried or burned in violation of international law. This study experimentally shows that these materials could be recycled and mixed with soil to improve the mixture mechanical properties. A complete series of small-scale laboratory tests, including direct shear test, Brazilian tensile test, permeability test, and swelling test, was conducted to examine the possibility of reusing WTTFs as soil-reinforcing agents. Five different fiber percentages (FPs), i.e., 0%, 0.5%, 1%, 2%, and 4%, of soil dry weight were mixed with the soil and the mechanical behavior of the mixture was investigated. The test results suggest that adding fiber to the soil improves both its shear and tensile strengths. The material ductility increases by adding the fiber to the soil as well. Further, the soil mixed with the fiber has a greater permeability coefficient and has less swelling potential. The mixture with these improved mechanical properties can cause less lateral pressure in case of being used as a backfill material. As a result, rather than being buried or burned, these wastes could be utilized to enhance the mechanical properties of various types of soils in geotechnical applications. The testing procedures and results are reported, discussed, and compared with those from the literature. [ABSTRACT FROM AUTHOR]

Cracking risk of cementitious materials remains one of the serious problems in the construction and highway field. Here, a series of pH-sensitive microgels with different anionic content and crosslinking density have been successfully synthesized and applied in cement mortar. The absorption behavior and pH sensitivity of microgel in aqueous solutions were determined. The effects of microgel on hydration degree, autogenous shrinkage, and compressive strength of cement mortar were studied. Experimental results indicate that the microgel exhibits less desorption in the pore solution and releases water timely in pH from 12–13. Despite the different anionic content of microgels, the addition of microgel with moderate crosslinking density is 0.19%∼0.31% , which can alleviate the autogenous shrinkage of cement mortar. The compressive strength of mortar can be increased by about 5.7 MPa by the microgels with low anionic content and moderate crosslinking density, thereby showing excellent internal curing effect. [ABSTRACT FROM AUTHOR]

The present research investigated the impact of heavy metals such as lead (Pb2+), copper (Cu2+), and zinc (Zn2+) on different bentonite's characterization. Two types of bentonites, possessing a difference in physiognomies, were adopted for this objective. Interesting observations were extracted from the study; first, a decrement in the values of liquid limit (LL), swelling pressure (SPr), and swelling potential (SPo) was observed in both the bentonites. Also, a higher variability in the LL (36.3, 39.2, and 38.1% decrease), free swell (FS) (73.8%, 77.2%, and 80.0% decrease), and SPr (48.4%, 50.4%, and 54.4% decrease) was observed in presence of Pb, Cu and Zn for the bentonite with a higher LL, swelling capacity, specific surface area (SSA), cation exchange capacity (CEC), and montmorillonite content. Likewise, the time–swelling test confirmed a decline in the time consumed for primary swelling with a rise in heavy metal concentration. The void ratio–pressure study revealed lower void ratio values for samples with heavy metals than deionised (DI) water under any assigned pressure. On the other hand, this shrinkage in the void ratio was predominantly evident for Zn2+ and Cu2+ solutions, compared to Pb2+ solution. Furthermore, the compression index and time required for 90% of consolidation were found to vary inversely, whereas the coefficient of consolidation varied directly with the heavy metal concentrations. Finally, the unconfined compressive strength study at multiple concentration ranges (from 0 to 2,000 mg L−1) revealed a value higher than 200 kN/m2, the mandatory criteria for a liner material for application in landfills. The results obtained will aid in understanding the dynamics of heavy metals on the bentonites' characterization. [ABSTRACT FROM AUTHOR]

The time-dependent behavior of soft and problematic soils is a major concern as constructional fill geomaterial. Several researchers have been utilizing different admixture to stabilize soft soil. In this study, fly ash (FA) has been used as an admixture to investigate the time-dependent behavior of Indian montmorillonitic clay (BC) by considering its elastic-viscoplastic behavior. A series of oedometer tests have been carried out on the test specimens at different FA contents. Microstructural arrangement of the BC–FA matrix was investigated using scanning electron microscopy, X-ray powder diffraction, and Fourier transform infrared spectroscopy. The results indicate that the addition of FA increases the compression stiffness of the matrix and that the unloading–reloading index decrease continuously. Time-dependent parameters, that is, creep coefficient, swelling coefficient, and strain limit, are significantly reduced by the addition of FA. Results show that hydrated FA contents, which encounters BC soil, produce calcium silicate hydrate (C-S-H) gel due to pozzolanic reaction and form a dense BC–FA matrix. Microscopic study exhibits the contribution of specific minerals toward its elastic, plastic, and viscous behaviors. The results show that the constitutive elastic-viscoplastic model considering swelling (EVPS model) works well in predicting the long-term compressibility behavior of FA-blended soft soils. [ABSTRACT FROM AUTHOR]

This paper describes key research on expansive soils and the methods employed to characterize them; fallacies in the current characterization of expansive soils are also explained. Novel swell characterization models that account for hydro, chemical, and mechanical behaviors of soils are introduced and used to demonstrate in case studies to improve expansive soil stabilization practices. The first two case studies present the results of expansive soils stabilized by incorporating clay mineralogy and soluble soil sulfate measurements. An innovative design method for successful stabilization of expansive soil is introduced in the first case study, which incorporated both basic clay mineralogy and unsaturated soil behaviors as well as performance-based durability studies. Sulfate soil stabilization works on medium-to-high sulfate soils, including rigorous laboratory and field validation studies, are presented in the second case study. The third case study, which involves a steep earthen embankment built with expansive clayey soils and experiencing recurring surficial slope failures and maintenance issues, is also discussed. Forensic studies explaining the causes of slope failures and their mitigation methods are also included. All case studies reveal the need for detailed data about soil chemistry, including clay mineralogy and sulfate studies, to improve the current field stabilization and infrastructure design on expansive soils. The last section summarizes recent innovations for better health monitoring and management of civil infrastructure built on expansive soils using unmanned aerial vehicle platforms and visualization tools, which will be valuable for validating the application of new materials, designs, and construction processes. [ABSTRACT FROM AUTHOR]

Acid/alkali contamination of expansive soils, which has been probed in recent years, gives rise to unexpected structural failure when exposed. However, a systematic research aiming at evaluating volumetric behavior of natural illitic clays when subjected to acid/alkali solution as pore fluid and its microlevel analysis is not well established. A series of oedometer tests and microanalytical experiments (X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy) have been carried out to investigate the effects of acid and alkali contamination on swelling and compressibility of natural expansive clays from Heilongjiang province in China and to identify the underlying controlling mechanisms. Distilled water, sulfuric acid of pH 3, and caustic soda of pH 13 were selected as three different pore fluids. The results show that compared to samples inundated with water, specimens exhibit greater swelling and lower compressibility after being exposed to acid solution, and lower swelling and greater compressibility after being subjected to alkali solution. In three different soaking solutions, all samples present an increasing tendency for swelling deformation with dry density from 1.4 to 1.8 g/cm3, while the highest compressibility occurs at dry density around 1.5 g/cm3. The microanalysis revealed that soils undergo reactions, including desiliconization and cation exchange, due to the acid and alkali erosion, which correspondingly leads to changes in soil mineralogy and texture. Acid and alkali contamination results in disintegration and loose structure, and acid exerts more destructive impacts than alkali do. The sulfuric acid promoted the dissolution of tetrahedral cations, while the caustic soda improved the dissolution of octahedral cations. [ABSTRACT FROM AUTHOR]

Fine-grained soils that expand when in contact with water can be a major issue in some geotechnical situations, but the soil can be stabilized through chemical means by hydrated lime incorporation. However, there is not yet any rational dosage methodology that combines the effects of both lime content and porosity of the treated soil specimen to predict its behavior regarding swelling. Thus, the present research intends to assess the one-dimensional swelling response of an expansive fine-grained soil stabilized with lime. For this purpose, compacted soil–lime blends were molded with three distinct amounts of lime (2%, 4%, and 6%), compacted to three different dry unit weights (14, 15, and 16 kN/m3) and tested after 3 h of curing. The results show that lime content, porosity, and their interaction are statistically significant in altering the swelling behavior of the compacted blends. Moreover, both can be combined through the adjusted porosity/lime index and related to the one-dimensional swelling. As a result, a single unique relationship could be established between the swelling and the proposed index with a coefficient of correlation (R2) of 96%. This approach was also successfully employed in other fine-grained soils treated with lime as validation. [ABSTRACT FROM AUTHOR]

Expansive soils are suitable as backfill and buffer materials in engineered barrier systems to isolate heat-generating nuclear waste in deep geological formations. The canisters containing nuclear waste would be placed in tunnels excavated at a depth of several hundred meters. The expansive soil should provide enough swelling capacity to support the tunnel walls, thereby reducing the impact of the excavation-damaged zone on the long-term mechanical and flow-barrier performance. In addition to their swelling capacity, expansive soils are characterized by accumulating irreversible strain on suction cycles and by effects of microstructural swelling on water permeability that for backfill or buffer materials can significantly delay the time it takes to reach full saturation. To simulate these characteristics of expansive soils, a dual-structure constitutive model that includes two porosity levels is necessary. The authors present the formulation of a dual-structure model and describe its implementation into a coupled fluid flow and geomechanical numerical simulator. The authors use the Barcelona Basic Model (BBM), which is an elastoplastic constitutive model for unsaturated soils, to model the macrostructure, and it is assumed that the strains of the microstructure, which are volumetric and elastic, induce plastic strain to the macrostructure. The authors tested and demonstrated the capabilities of the implemented dual-structure model by modeling and reproducing observed behavior in two laboratory tests of expansive clay. As observed in the experiments, the simulations yielded nonreversible strain accumulation with suction cycles and a decreasing swelling capacity with increasing confining stress. Finally, the authors modeled, for the first time using a dual-structure model, the long-term (100,000 years) performance of a generic heat-generating nuclear waste repository with waste emplacement in horizontal tunnels backfilled with expansive clay and hosted in a clay rock formation. The thermo-hydro-mechanical results of the dual-structure model were compared with those of the standard single-structure BBM. The main difference between the simulation results from the two models is that the dual-structure model predicted a time to fully saturate the expansive clay barrier on the order of thousands of years, whereas the standard single-structure BBM yielded a time on the order of tens of years. These examples show that a dual-structure model, such as the one presented here, is necessary to properly model the thermo-hydro-mechanical behavior of expansive soils. [ABSTRACT FROM AUTHOR]

In this work, the swelling behavior of sodium (Na)-montmorillonite clay with increasing amounts of hydration is studied using molecular dynamics. The molecular models of the dry clay and the hydrated clays, consisting of 2, 4, 6, 8, and 10 monolayers of water in the interlayer, are used in this study. This work captures the evolution of interaction energies in the interlayer of Na-montmorillonite swelling clay with increasing hydration and provides insight into swelling mechanisms. This work shows the important role of bound water and clay-Na interactions during swelling to stabilize clay structure during hydration. Changes to water molecule conformations in the interlayer during swelling are also reported. The results and insight provided by this work will help in modeling and predicting exfoliation and resulting particle breakdown in swelling clays, in addition to expounding the key role of interlayer interactions on swelling in smectite clays. [ABSTRACT FROM AUTHOR]

The present investigation examines the efficiency of an in situ lime precipitation technique in stabilizing expansive soil through laboratory-scale model tests. Expansive soil was compacted in a cylindrical mold and sequentially permeated with CaCl2 and NaOH solutions into the expansive soil through a central hole filled with coarse sand. Successive permeation of CaCl2 and NaOH solutions into the compacted expansive soil resulted in precipitation of lime in the expansive soil mass. The precipitated lime reduced the plasticity index, controlled the swell-shrink potentials, and increased the unconfined compressive strength of the expansive soil by both strong lime modification reactions and soil-lime pozzolanic reactions. The results are corroborated with microfabric studies on lime precipitation treated specimens, which showed the formation of cementation bonds. [ABSTRACT FROM AUTHOR]

Determination of consolidation properties of compacted lime-treated cohesive clays by the one-dimensional fixed-ring oedometer consolidation method with conventional load increment duration may not be appropriate due to immediate pozzolanic reactions, which occur in the presence of lime. An attempt has thus been made to study the effect of accelerated loading on the compressibility characteristics of two different cohesive clays originating from diversified terrains of Saudi Arabia, before and after treating them with lime. In order to study the extent of improvement on the strength characteristics upon lime treatment, a series of unconfined compression strength tests are also carried out. The effect of lime treatment on the elastic moduli has also been studied. It is observed that, prior to any treatment, the final equilibrium void ratio values increase with the increase in duration of loading for the soils. The addition of lime significantly affects the compressibility behavior of both the soils. The unconfined compressive strength and elastic moduli (initial tangent and secant moduli) values increased with an increase in lime content and curing period. [ABSTRACT FROM AUTHOR]

This paper examines the use of ladle furnace steelmaking slag (LFS) as a material for the construction of embankments in civil works. It reports the chemical, mineralogical, and geotechnical properties of two soils, two LFS, and various mixtures thereof, in addition to their volumetric stability. The findings show that lengthy periods of time are required to achieve the potential expansion of LFS because of the hydration of certain aluminates and calcium oxide in addition to the slow hydrocarbonation reactions of magnesium oxide. The expansion test on the soil-LFS mixtures revealed slight swelling, attributable to the pozzolanic reactions of clay minerals with portlandite and brucite in addition to accommodation within the soil-slag pore structure. The cation exchange capacity of clay minerals affects the interaction between soil and LFS; minerals such as montmorillonite, with a high cation exchange capacity, improve the California bearing ratio and reduce the potential expansion. Not all soils are suitable for improvement with LFS because of the mineral compounds of their clay fraction. [ABSTRACT FROM AUTHOR]

Lime stabilization prevails to be the most widely adopted in situ stabilization method for controlling the swell-shrink potentials of expansive soils despite construction difficulties and its ineffectiveness in certain conditions. In addition to the in situ stabilization methods presently practiced, it is theoretically possible to facilitate in situ precipitation of lime in soil by successive permeation of calcium chloride () and sodium hydroxide (NaOH) solutions into the expansive soil. In this laboratory investigation, an attempt is made to study the precipitation of lime in soil by successive mixing of and NaOH solutions with the expansive soil in two different sequences. Experimental results indicated that in situ precipitation of lime in soil by sequential mixing of and NaOH solutions with expansive soil developed strong lime-modification and soil-lime pozzolanic reactions. The lime-modification reactions together with the poorly developed cementation products controlled the swelling potential, reduced the plasticity index, and increased the unconfined compressive strength of the expansive clay cured for 24 h. Comparatively, both lime-modification reactions and well-developed crystalline cementation products (formed by lime-soil pozzolanic reactions) contributed to the marked increase in the unconfined compressive strength of the expansive soil that was cured for 7-21 days. Results also show that the sequential mixing of expansive soil with solution followed by NaOH solution is more effective than mixing expansive soil with NaOH solution followed by solution. [ABSTRACT FROM AUTHOR]

The development of strain in two 31 and 56 m long instrumented postdriving grouted cylinder piles at a site west of Busan, South Korea, were monitored during 200 days after construction, whereupon a static loading test was performed. Initial strain measurements showed unexpected elongation of the pile, probably due to swelling from absorption of water but as the soil reconsolidated, the elongation changed into shortening, probably due to imposed residual load in the pile. The resulting compression of the pile eventually offset the swelling of the pile. To investigate the cause of the strain changes more closely and enhance the evaluation of the field data, two short pile pieces were prepared and placed free-standing above ground in an outside laboratory. One piece was from a cylinder pile of which central void was grouted and one was made up by grouting inside a temporary casing. The monitoring showed that the short pieces appeared first to shorten and then to elongate due to the heating and cooling from the hydration process. When strains and temperature had stabilized 150 days after start of the study, both pieces were submerged to introduce swelling of the concrete. For the first 100 days after submerging, the swelling strains in both short pieces amounted to 100 μ[variant_greek_epsilon]. Seven hundred days after submersion, the total swelling strains were 150 and 250 μ[variant_greek_epsilon]. [ABSTRACT FROM AUTHOR]

Earlier studies have established that aggregates could be produced from fly ash through pelletization, which has the advantages of reducing (1) environmental pollution and (2) consumption of depleting natural aggregates. Though cement, lime, and bentonite were used for improving the properties of fly ash aggregates, limited studies have been reported on the effect of binders on the pelletization process of fly ash. This paper discusses the relative performance of bentonite with two different swelling characteristics on the pelletization of fly ash. The variation of factors and its optimum level on the overall pelletization efficiency, efficiency of producing three individual size fractions, ten percent fines value, and water absorption were determined through a statistically designed experiment using response surface methodology. The maximum pelletization efficiency of fly ash aggregate was achieved with lower dosage level of high swelling bentonite. Higher factor levels facilitate enhanced ball growth, i.e., produce aggregate size fraction greater than 10 mm. Similarly, the maximum ten percent fines value and minimum water absorption result at the maximum level of the factors studied. The optimal level of factors for a given aggregate size fraction was almost similar, independent of swelling characteristics of bentonite, except for the variation in bentonite and moisture contents. [ABSTRACT FROM AUTHOR]

Soil water retention is a critical factor influencing irrigation decisions and hence agricultural crop yields. However, information on soil water retention characteristics (SWRC) is seldom available for irrigation planning, crop yield modeling, or hydrological simulations, especially for problematic soils, such as seasonally impounded shrink-swell soils. As large scale direct measurement of SWRC is not viable due to a number of reasons, researchers have developed pedotransfer functions (PTFs) to estimate SWRC from easily measured soil properties, such as texture, organic matter content, bulk density, etc. However, PTF applicability in locations other than those of data collection has been rarely reported. One of the most recent PTFs that has shown overall reasonable predictions in evaluation studies is Rosetta, a numerical code for estimating soil hydraulic parameters with hierarchical pedotransfer functions. Relatively, the development of large databases makes it one of the widely used PTFs. If validated for spatial application, it has immense use potential in countries like India, where data on soil hydraulic properties are seldom available, a deficiency that hampers better simulations in processes, like partitioning runoff and infiltration, assessing evapotranspiration, irrigation scheduling, etc. Rosetta is also relatively flexible allowing estimation of hydraulic properties from easily available minimum input of textural fractions. This study was conducted to evaluate (1) an applicability of four widely used soil water retention functions to describe SWRC; and (2) the computer program Rosetta for its validity. Statistical indices, i.e., root mean square error (RMSE), mean absolute error, maximum absolute error, and degree of agreement (d) were computed to evaluate “goodness-of-fit” of the four functions to the measured SWRC data. These indices were also used to compare measured SWRC with estimates of SWRC by Rosetta. For soil samples collected from 41 profiles, 175 SWRC were measured in the laboratory. The van Genuchten function fitted relatively better (RMSE=0.052 m3 m-3) to SWRC of clay soils, whereas the Brooks–Corey (BC) function was better in expressing SWRC of clay loam and sandy clay loam soils with RMSE=0.06 and 0.07 m3 m-3, respectively. Campbell and Cass–Hutson (CH) functions were of intermediate value. Worst performing functions were BC (clay soils), Campbell (clay loam), and CH (sandy clay loam) with corresponding RMSE=0.059, 0.065, and 0.077 m3 m-3. Estimates of two important points on the SWRC curve, i.e., field capacity and permanent wilting point were predicted with relatively better accuracy for clay and sandy clay loam soils by all the four functions. RMSE and d ranged from 0.027 to 0.043 m3 m-3 and from 0.73 to 0.88 for clay soils. Corresponding values for sandy clay loam soils were 0.008 –0.019 m3 m-3, and 0.92–0.98. However, in clay loam soils, only two functions were found suitable. Estimates of SWRC obtained by applying hierarchical rules in Rosetta were reliable (RMSE<0.05 m3 m-3). Magnitude of average RMSE increased progressively in clay loam, clay and sandy clay loam soils (0.028<0.035<0.042 m3 m-3). The study established that SWRC of the “Haveli” soils could be estimated using generic PTF and thus information that is prerequisite in simulating hydrological processes occurring in seasonally impounded soils could be acquired. [ABSTRACT FROM AUTHOR]

A laboratory index defined as gravimetric water content at ambient relative humidity of 75% (w75) is proposed for qualitatively classifying the swelling potential of clays and clayey soils (e.g., low, moderate, high). The methodology is calibrated by comparison with existing plasticity-based and suction-based classification methodologies for a series of natural clays from Missouri and Colorado and clay mixtures prepared to represent a wide range of swelling potential. Procedures are described for obtaining w75 by placing samples in the headspace of an environmental chamber maintained under controlled humidity using a saturated NaCl solution. The proposed methodology has potential advantages over existing expansive soil classification methods because a large number of samples may be tested concurrently, no specialized testing equipment is required, and testing procedures may be readily automated. Measurements may be obtained in as little as 3–5 days with coefficients of variation ranging from 5 to 25%. [ABSTRACT FROM AUTHOR]

Among the several remedial techniques suggested to combat the damages caused by expansive soils, the use of sand cushion and cohesive nonswelling (CNS) soil cushion were widely accepted, especially for light weight structures such as floorings, pavements, and canal linings, which cover large areas. CNS cushion is preferred to sand cushion in view of the sceptical performance of sand cushion at several work sites. However, various investigators have reported the nonavailability of suitable CNS materials at many project sites and in such circumstances, it is also suggested to prepare the artificial CNS materials by mixing suitable admixtures to the native clay. The present work deals with the modification of black cotton soil using CaCl2 and rice-husk-ash (RHA), which resulted in two favorable combinations of soil +0.5%CaCl2+8% RHA and soil +1%CaCl2+6% RHA with nonswelling properties, while retaining high unconfined compressive strength values. The mix of soil +0.5%CaCl2+8% RHA was taken for further study in view of its economy due to lower CaCl2 content. The field heave measurements of footings, pavement slabs, and canal lining panels cushioned with the proposed chemically stabilized soil (CSS) mix revealed that the CSS cushion can effectively reduce their heave and hence it can be recommended as an alternative to conventional CNS cushion in localities of scarcity for suitable CNS materials. [ABSTRACT FROM AUTHOR]

Compacted bentonite and sand-bentonite mixtures are sought as buffer and backfill materials for high-level radioactive waste disposal facilities because they have very low permeability. To establish specifications such as the dry density and sand-bentonite mass ratio for buffer and backfill materials, we must quantitatively evaluate a material’s hydraulic conductivities. This study presents theoretical new equations for evaluating the hydraulic conductivity of compacted bentonites and sand-bentonite mixtures. New equations are proposed for evaluating the flow velocity of interlayer water between two montmorillonite parallel-plate layers considering the swelling behaviors of montmorillonite. Furthermore, a prediction method for hydraulic conductivity of compacted bentonite and sand-bentonite mixtures is presented by combining new equations with previous equations for evaluating swelling behavior of montmorillonite in bentonite. The applicability of this method is clarified by comparing predicted results with experimental data reported by previous research on hydraulic conductivities of compacted bentonites and sand-bentonite mixtures. [ABSTRACT FROM AUTHOR]

This note describes a triaxial apparatus that applies liquid infiltration under automatically controlled boundary conditions while using the new Xeritron sensor to measure suction. Three different infiltration boundary conditions of interest including constant mean stress (CMS), constant volume (CV), and constant stiffness (CS) are applied to examine the influence of boundary conditions on the mechanical and hydraulic behavior of unsaturated clay materials. CMS and CV tests provide limits of infiltration boundary conditions while CS tests represent a flexible spring-type boundary condition. Spatial distribution of gravimetric water content and bulk density are measured to calculate dry density and degree of saturation following testing to determine internal changes to the specimens. The results from initial testing show that the apparatus is providing experimental evidence to evaluate unsaturated flow models and elastic-plastic constitutive models to examine the behavior of swelling clay soils under varying confinement conditions. [ABSTRACT FROM AUTHOR]

Samples of geosynthetic clay liners (GCLs) from four landfill covers were tested for water content, swell index, hydraulic conductivity, and exchangeable cations. Exchange of Ca and Mg for Na occurred in all of the exhumed GCLs, and the bentonite had a swell index similar to that for Ca or Mg bentonite. Hydraulic conductivities of the GCLs varied over 5 orders of magnitude regardless of cover soil thickness or presence of a geomembrane. Hydraulic conductivity was strongly related to the water content at the time of sampling. Controlled desiccation and rehydration of exhumed GCLs that had low hydraulic conductivity (10-9 to 10-7 cm/s) resulted in increases in hydraulic conductivity of 1.5–4 orders of magnitude, even with overburden pressure simulating a 1-m-thick cover. Comparison of these data with other data from the United States and Europe indicates that exchange of Ca and/or Mg for Na is likely to occur in the field unless the overlying cover soil is sodic (sodium rich). The comparison also shows that hydraulic conductivities on the order of 10-6 to 10-4 cm/s should be expected if exchange occurs coincidently with dehydration, and the effects of dehydration are permanent once the water content of the GCL drops below approximately 100%. Evaluation of the field data also shows that covering a GCL with a soil layer 750–1,000 mm thick or with a geomembrane overlain by soil does not ensure protection against ion exchange or large increases in hydraulic conductivity. [ABSTRACT FROM AUTHOR]

Lime continues to be one of the most popular chemical admixtures used to modify expansive clays despite the associated mixing and pulverization problems. In the present investigation, the efficacy of CaCl2 in place of conventionally used lime is studied by conducting laboratory and field tests. These investigations were carried out on the slopes of a trapezoidal trench made in expansive clay bed. Heave measurements were taken on the lime and CaCl2 treated slopes and also on untreated slopes for four consecutive cycles of wetting and drying. The field cyclic seasonal movements and the subsequent laboratory tests on undisturbed and disturbed soil samples revealed that the CaCl2 could be a promising chemical modifier instead of conventionally used lime, not only due to its multifold influence on heave control, plasticity reduction, and swell properties but also its easy application in the form of solution without any need for pulverization and mixing. Though an apparent reduction in unconfined compressive strength of treated samples is observed, the drained triaxial tests on treated and untreated samples revealed that there is an increase in the angle of internal friction of treated samples. [ABSTRACT FROM AUTHOR]

This paper presents, by way of comparison, the effect of fly ash on the volume change of two different types of clay, one a highly plastic expansive clay and the other a nonexpansive clay, also of high plasticity. Expansive clays swell on absorbing water and shrink on drying. Nonexpansive clays undergo large compression at high water contents. The effect of fly ash content on free swell index, swell potential, and swelling pressure of expansive clays was studied. Compression index and secondary consolidation characteristics of both expansive and nonexpansive clays were also determined. Swell potential and swelling pressure, when determined at constant dry unit weight of the sample (mixture), decreased by nearly 50% and, when determined at constant weight of clay, increased by nearly 60% at 20% fly ash content. Compression index and coefficient of secondary consolidation of both the clays decreased by 40% at 20% fly ash content. [ABSTRACT FROM AUTHOR]

Physicochemical interactions between polymer molecules and clay particles affect the swelling rate and magnitude of expansive clay soils. The effectiveness of aqueous solutions of three polymers: Sodium carboxymethyl cellulose (CMC), polyacrylamide (PAM), polyethylene oxide (PEO) ranging in concentration from 0.5 to 10 g/L, as soil stabilization agents against Na-montmorillonite swelling was analyzed. Rates of volumetric swelling of Na-montmorillonite upon hydration were recorded over durations ranging from 120 to 200 h, and data were used to compute the volumetric swelling ratio (VSR), an expression of the clay volume at any time relative to the initial volume of clay in the immersion tube. The results show that PAM, the cationic polymer reduces the VSR by as much as 40% relative to distilled water. PAM molecular weight and concentration have minimal effects on VSR although sorption of PAM of higher molecular weight (PAM B) is favored at aqueous concentration below 2 g/L. Data from x-ray diffraction and batch sorption tests on dried Na-montmorillonite samples indicate that postsorption/swelling interlayer spacings of 0.74 and 0.78 nm for PAM A (molecular weight=4×106) and PAM B (molecular weight=7×106) respectively, are attained through fixation of PAM molecules in clay interlayer space during sorption at an aqueous concentration of 4 g/L. Test results for CMC (the anionic polymer) and PEO (the neutral polymer) show that swelling is not significantly reduced relative to that of distilled water. PAM can be used at aqueous concentrations between 0.5 and 4 g/L as an effective stabilization agent for expansive soils. [ABSTRACT FROM AUTHOR]

Alkali-silica reaction (ASR) is a concrete pathology due to chemical reactions involving reactive silica from reactive aggregates and the inner solution of concrete. Main effects are swelling, cracking, and reduction in the mechanical properties of affected concretes. Water is very important for ASR; the more available water, the more expansion and degradation. This article presents new laws for modeling of the influence of water upon ASR. They are based on experimental results and then used to simulate results taken out of the scientific literature. [ABSTRACT FROM AUTHOR]

An understanding of microanalytical characterizations would be useful to explain the hydraulic behavior of water across the slaked mudstone liner. It is further expected that the mudstone material could be designed for replacing clay material as a natural landfill liner. The result of the semidynamic leach test indicated that the released sodium species are very rapid and large. The microanalysis of the eroded mudstone indicated many white short rod-like conglomerates. The x-ray diffraction examination clearly illustrated that the white crystalline compound is sodium sulfate. Other micrographs indicated that many petal-like grains are present in the permeated mudstone. In addition, the microchemical result revealed that the flat-like grain could be a sand phase and the petal-like structure is possibly a clay phase (illite). Therefore, it is inferred that the possible characterizations of the eroded and slaked mudstone are stated as follows. The swelling and slaking behaviors of the mudstone possibly contributed to the dissolution of sodium sulfate. The surface of the permeated mudstone might present a lot of clay phases (illite) to reduce water permeation. Thus, the slaked mudstone as a natural landfill liner is feasible. [ABSTRACT FROM AUTHOR]

The engineering properties of expansive soils are conventionally improved through the use of additives such as fly ash, lime, and chemical additives. Such soils are often referred to as stabilized or modified or treated expansive soils. The soil-water characteristic curves (SWCC) of two expansive soils from Texas were measured both in natural and stabilized conditions using the pressure plate apparatus in the suction range of 0-1,000 kPa. The SWCC results are used to interpret the expansive soil behavior due to stabilizer treatment. In addition, relationships were developed between the basic soil and stabilizer properties such as water content, dry density, liquid limit, plastic limit, and stabilizer dosages and the model constants of the SWCC formulation of Fredlund and Xing via multiple linear regression analysis. The analysis showed that higher coefficients of correlations can be achieved by using six independent soil properties. The comparisons between the predicted and measured volumetric water contents are within ±20% for ash-treated expansive soils, and within ±15% for combined ash- and fiber-treated expansive soils. The research data and interpretation analysis presented here can be extended to understand volume change behaviors of other stabilized expansive soils using the SWCC test data. [ABSTRACT FROM AUTHOR]

Three index properties (liquid limit, sedimentation volume, and swell index) of two sodium bentonites from geosynthetic clay liners (GCLs) are correlated with the hydraulic conductivity (k) of the same GCLs to evaluate the suitability of index properties for evaluating chemical compatibility. Deionized water (DIW) and calcium chloride (CaCl2) solutions were used for hydration (index tests) and permeation (hydraulic conductivity tests). In general, increasing the CaCl2 concentration caused each index property to decrease and the hydraulic conductivity to increase relative to values obtained with DIW, with the strongest correlations obtained with the liquid limit. The correspondence between index properties and hydraulic conductivity differed by index property, the quality of the bentonite, and the effective stress applied during the hydraulic conductivity test. Thus, correlations used for compatibility assessments are specific to the bentonite in the GCL and the stress conditions being applied. Results of the study also show that appreciable changes in hydraulic conductivity can occur with little or no change in index properties and that the greatest changes in index properties may correspond to conditions causing low or modest changes in hydraulic conductivity. However, in this study, a critical threshold existed for each index property, beyond which further decreases in an index property correlated with substantial increases (>10×) in hydraulic conductivity. [ABSTRACT FROM AUTHOR]

Civil infrastructure in the foothills of the Rocky Mountains faces a unique geological hazard arising from underlying beds of steeply dipping expansive bedrock. Efforts to mitigate damaging differential movements that commonly occur among adjacent bedrock strata near the surface typically involve overexcavation and recompaction of the in situ materials as engineered fill. This paper examines the practice by quantifying the swelling-related properties of two dissimilar bedrock end members obtained from a site near Denver, Colo. where overexcavation is warranted. Atterberg limits, compaction, suction, and volume change (shrinkage) tests are conducted for each end member and several mixtures prepared to represent the wide range of subsurface conditions expected in the region. The objective is to examine the extent to which properties of the remolded fill may be predicted from the properties and relative amounts of the end member materials comprising it. Linear relationships are found between end member mass fraction and each of the properties measured [liquid limit, plasticity limit, plasticity index, wopt, (ρd)max, Δψt/Δw, and Ch], thus providing a quantitative basis for simplifying the design of future overexcavation programs. Optimum moisture content occurs at 90% saturation regardless of bentonite mass fraction. Suction compression index (Ch) for compacted specimens is found insensitive to molding water content. [ABSTRACT FROM AUTHOR]

Within the last decade several studies have been conducted to evaluate the geotechnical properties of bottom ash obtained from electric utilities burning pulverized coal amended with admixtures such as clay, bentonite, and lime. Most of these studies concentrated on evaluating strength and stiffness characteristics of the mixtures. Because of the high volume change characteristics of bentonite and clay, improper and/or excessive use of these admixtures can impart significant swelling characteristics to the mixtures. This study was conducted to evaluate the swelling properties of two bottom ash-bentonite mixtures compacted at various initial moisture contents. Results from this detailed investigation show that the swelling potential increased with the increase in bentonite content and decreased with the increase in initial moisture content. Mixtures with 20% bentonite were observed to have volume change characteristics that may not be suitable for some lightly loaded structures. Mixtures with 15% bentonite; compacted at initial moisture contents of 18% or higher; were observed to have less than 4% free swell, whereas for mixtures compacted at an initial moisture content of 16% or lower, the percent increase in free swell was observed to be greater than 7%. [ABSTRACT FROM AUTHOR]