Soil Bentonite Research Articles

Laboratory investigation of the swelling pressure of bentonite with quicklime and hydrated lime using ASTM-4546-96 and constant volume methods

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.

Analytical Solution for Contaminant Transport through a Soil–Bentonite (SB)/Geosynthetic Clay Liner (GCL)/Soil–Bentonite (SB) Composite Cutoff Wall and an Aquifer

This study develops a one-dimensional analytical solution for contaminant advection, diffusion and adsorption through a soil–bentonite (SB)/geosynthetic clay liner (GCL)/SB–aquifer composite cutoff wall (CCW) system. The solution agrees well with an existing double-layer model. Adopting toluene as a representative contaminant, using the present solution, the analysis systematically investigates the impact of hydraulic gradient (i) and the hydraulic conductivities of GCL (kgcl) and SB (ksb). The results show the following: (1) Increasing i from 0.1 to 1 reduces the concentration breakthrough time (tcb) from 20 to 11 years and mass flux breakthrough time (tfb) from infinite to 11 years, indicating lower i significantly extend both tcb and tfb, which is crucial for optimizing CCW barrier performance; (2) lowering kgcl from 5.0 × 10−11 m/s to 1 × 10−12 m/s and reducing ksb from 1.0 × 10−9 m/s to 1.0 × 10−11 m/s, would increase the tcb by 36% and 100%, respectively. It demonstrates that reducing kgcl and ksb could enhance barrier performance. (3) To achieve equivalent barrier performance, soil–bentonite cutoff wall (SBCW) requires greater thickness compared to SB/GCL/SB CCW, indicating that GCL reduces the required amount of bentonite; and (4) CCWs can use SB with lower adsorption capacity to achieve equivalent performance, further reducing bentonite requirements. The present solution can aid in the design and optimization of GCL-enhanced CCWs.

Effects of ionic strength and bentonite ratio on the migration of Cr(VI) in clayey soil-bentonite engineered barrier.

Soil-bentonite (S-B) barriers have been widely used for heavy metal pollution containment. This study conducted batch adsorption tests and diffusion-through tests to evaluate how ionic strength and bentonite ratio influence the migration of Cr(VI) in natural clay-bentonite mixtures. The test results indicated that the adsorption of Cr(VI) exhibited an obvious anion adsorption effect, the pH of the soil mixture increased with the addition of bentonite, resulting in a decrease in the positive surface charge. This change led to a decrease in Cr(VI) adsorption capacity, from 775.19 mg/kg for pure clay to 378 mg/kg for mixture samples with excessive bentonite. Furthermore, as the ionic strength increases from 0 to 0.1 M, the Cr(VI) adsorption capacity increases slightly due to the weakening of electrostatic repulsion on the clay particle surface, but the effective diffusion coefficient (De) increases by 21.97%. The compression of the diffusion double layer (DDL) under high ionic strength conditions enlarges the diffusion path and enhances the migration of Cr(VI) through the pore flow paths. Moreover, hydrated bentonite effectively fills the interaggregate pores of natural clay, thus creating narrower and more tortuous flow paths. However, excessive bentonite increases the pH value and pore volume, resulting in changes to the soil microstructure and disrupting the continuous skeleton of natural clay, which is unfavorable for Cr(VI) containment. Based on the study of the Cr(VI) contaminated site, a bentonite ratio of 2:10 is recommended for optimal natural performance of the natural clay-bentonite barrier.

Centrifuge Modeling of Backfill Consolidation in Soil-bentonite Cutoff Walls

Soil-bentonite (SB) is commonly adopted for the backfill of vertical cutoff walls to contain contaminated groundwater. The permeability of SB backfill is dependent on its effective stress state, which is affected by the backfill consolidation process. This paper presents a geotechnical centrifuge model test to simulate the primary consolidation of typical SB cutoff walls with the advantages of reduced scale in time and size. The moisture content and earth pressure of the wall were monitored at varied depths. Test results showed that the rapid consolidation stage developed swiftly and various consolidation indicators exhibited significant development. Within the buried depth over the half (approximately two-thirds), the distribution of vertical effective stress was similar to the Bucknell field testing results, namely that it increased nonlinearly and then tended to stabilize. Also, the cumulative effect of lateral frictional resistance increased with depth and reached its peak value. In the deeper buried areas, lateral frictional resistance decreased sharply before increasing again with increasing depth, while vertical effective stress followed a pattern of significant increase followed by a decrease. This centrifuge test may be useful for achieving a comprehensive evaluation of the consolidation behaviour and mechanism of SB cutoff walls.

Evidence of nuclide migration from high-level radioactive waste glass via geogas

Characteristics of high-level radioactive waste transport in glass as gases were studied. A transmission electron microscope was used to observe the morphology of the substance after penetrating the high-level radioactive waste glass and the bentonite soil column, and the composition of the substance was analyzed using electron probe energy spectroscopy. The results show that the radionuclides in the high-level radioactive waste glass were transported out of the glass, the bentonite was penetrated by the geogas, and the transported substance occurred as nanometer-size particles and particle aggregates.

Mechanical properties of bentonite soil stabilized with rice husk ash and ground granulated blast furnace slag geopolymer

Mechanical properties of bentonite soil stabilized with rice husk ash and ground granulated blast furnace slag geopolymer

Sand-bentonite backfill amended with composite polymer exposed to organic acid: Hydraulic performance and microstructural properties

Soil-bentonite (SB) backfills in vertical cutoff walls are used extensively to contain contaminated groundwater. Previous studies show that the hydraulic conductivity of backfill can exceed the typically recommended maximum value (k = 1 × 10−9 m/s) if exposed to groundwater impacted by organic acids commonly released from uncontrolled landfills and municipal solid waste dumps. Polymer amended backfills exhibit excellent chemical compatibility to metal-laden groundwater. However, few studies to date have explored the effect of organic acid contaminated groundwater on hydraulic performance of polymer amended backfills. This study presents an experimental investigation on the hydraulic performance and microstructural properties of a composite polymer amended backfill used to contain flow of acetic acid-laden groundwater. A series of laboratory experiments were performed to evaluate free-swell indices of the composite polymer amended bentonites, liquid limits of the composite polymer amended and unamended bentonites, and slump heights and hydraulic conductivity (k) values of the amended backfills to acetic acid solutions with varying concentrations. The results were compared with those of the unamended bentonites and unamended backfills reported in a previous study. The results showed that the free-swell index and liquid limit of the amended bentonites were higher than those of the unamended bentonites. Permeation with acetic acid solutions with concentrations ranging from 40 mmol/L to 320 mmol/L conducted on the amended backfill only resulted in an increase in k of less than a factor of about 10 related to that based on permeation with tap water (1.68 × 10−10 -4.41 × 10−11 m/s to acetic acid solution versus 1.65 × 10−11 m/s to tap water). Mechanisms contributing to enhanced chemical compatibility of amended backfill were ascertained based on scanning electron microscopy, mercury intrusion porosimetry, and zeta potential analyses.

Assessment of Two SWCC models for predicting the curve fitting parameters of lateritic soil: bentonite mixtures

This study compares the capabilities of soil water characteristic curve (SWCC) models by Brooks-Corey (BC) and van Genuchten (vG) in estimating the curve fitting parameters for lateritic soil—bentonite mixtures. The SWCCs of soil treated with 0–10% bentonite and compacted with British standard light (BSL) energy at compaction states representing dry of optimum, optimum, and wet of optimum conditions were measured by sequential desorption using pressure plate extractor. The fitting parameters of the two equations were determined by a non-linear fitting program. The fitting capabilities of the models on the measured data were compared by statistical indices namely the root mean square error (RMSE), linearity (R2) and index of agreement (d). Results revealed that volumetric water content increased as bentonite content increased with specimens containing 10% bentonite recording the highest and therefore has greater capacity to retain water/contaminants, while the air entry value (AEV) for the various soil mixtures also increased with higher bentonite content. The study also found that the estimated volumetric water contents approximated the measured values at all suctions with a high degree of accuracy with RMSE values that ranged from 0.0035 to 0.0150 for vG model which are somewhat lower than the values for BC equation. Similarly, R2 for the vG equation (≥ 0.99) are, on average, slightly higher than those of the BC fits. However, the d values associated with the BC model which varied between 0.788 and 0.971 are higher than those of the vG (0.784–0.968). Overall, the study established that the vG model proved marginally superior in respect of goodness of fit.

Effects of Freeze–Thaw Cycle on Permeability and Compression Properties of Aeolian Soil–Bentonite Mixture

Effects of Freeze–Thaw Cycle on Permeability and Compression Properties of Aeolian Soil–Bentonite Mixture

Maximizing wheat yield through soil quality enhancement: A combined approach with Azospirillum brasilense and bentonite

Maintaining soil fertility to obtain higher crop production is essential for food security and sustainability. Soil amendments not only improve soil fertility but also enhance plant growth. Azospirillum brasilense is an important plant growth-promoting rhizobacteria participating in the progression of wheat (Triticum aestivum) yield; however, how it works in bentonite soil for enhancing wheat production is not clear yet. To investigate the combined applications of Azospirillum brasilense and bentonite, a planned experiment was performed in the wirehouse. Through studying various agronomic, physiological, and soil-related parameters, it was found that the sole application of Azospirillum brasilense is more beneficial as compared to the sole application of ben-tonite. Bentonite application at 10 g kg−1 of soil is more beneficial for the wheat crop growth and soil fertility status as compared to the bentonite application at 5 g kg−1 of soil. Co-application of Azospirillum brasilense and bentonite at 10 g kg−1 of soil increases the grain yield by 42 %, LAI by 20.2 %, and Stomatal conductance by up to 13.88 %. The resulting increase was due to an increase in the soil organic matter contents, microbial activities, growth hormones production, and more availability of soil water for plant growth.

Impact of Nano-Silica and Cement on Geotechnical Properties of Bentonite Soil

Impact of Nano-Silica and Cement on Geotechnical Properties of Bentonite Soil

Effects of the Types and Amounts of Clay Minerals on Durability of Lime-Stabilized Clay Soils

Although the interaction between clay minerals and lime is the most effective factor in lime stabilization techniques, it has not been deeply evaluated. This research study investigated the microstructural characteristics of lime-stabilized Bentonite and Kaolin soils using X-ray diffraction (XRD), scanning electron microscope (SEM), and energy dispersive X-ray (EDX) analyses. To consider the variation in clay mineralogy, these soils were mixed at varied ratios, stabilized, and then subjected to a durability process. The microstructural findings showed that the pozzolanic reactions with lime did not occur or occurred at a low level for Bentonite soil. However, they occurred at a very high level for Kaolin soil. The durability test confirmed the microstructural results and showed that the samples in which Bentonite soil had a share of 40 to 100% by dry weight of the soil did not last with any percent of lime. When the Kaolin soil content reached 100% by dry weight of the soil, the specimens lasted in the best possible way, even with 4% of the lime. This study concluded that the determination of optimum lime content based on the amounts and types of soil clay minerals is an important innovation for geotechnical projects and may be very cost-effective.

Analytical solution for contaminant transport through a GCL-enhanced composite cutoff wall system

The geosynthetic clay liners (GCLs) have been recently shown to be effective in cutoff wall applications. Yet, its influence on contaminant transport through cutoff wall system is rarely reported. This study presents an analytical solution for the transport of organic contaminant through a composite cutoff wall system comprising a soil-bentonite wall, a GCL, and an aquifer. The analytical solution was obtained by variable separation method and verified against an existing analytical solution and a numerical solution. Parametric analysis was conducted to elucidate the effects of GCL, soil-bentonite (SB) wall thickness (Lw), aquifer thickness (La), and contaminant half-life (t1/2) on contaminant transport. The results show that by adding a GCL layer, the contaminant concentration and the maximum flux can be significantly decreased. When the GCL retardation factor increases 1 to 300, the required time to reach the maximum flux is delayed from about 62 years to 1500 years. Larger aquifer thickness sufficiently weakens the contaminant transport process. Under the same breakthrough criteria, the required thickness of SB wall decreases by about 20% when the GCL retardation factor increases from 1 to 50. The proposed analytical solution provides a useful tool for the design of the SB-GCL cutoff wall system.

Hydro-mechanical behavior and microstructure evolution of red clay-bentonite backfills

Soil-bentonite (SB) cutoff walls have been extensively used as vertical engineering barriers to control groundwater flow and subsurface contaminant migration. As the pollution containment capability of the SB backfills is intimately related to the hydro-mechanical behavior, consolidation tests and hydraulic conductivity tests were carried out to investigate the effects of bentonite content on the hydro-mechanical behavior of red clay-bentonite backfills, and the microstructure evolution of backfills under vertical loading was evaluated based on mercury intrusion porosimetry (MIP) tests and field emission scanning electron microscope (FESEM) observations. The results of microstructure analysis also evaluated the influence of bentonite on the clay fabric which changed the relationship between hydraulic conductivity and void ratio. The results indicated that the void ratio and hydraulic conductivity decreased linearly with the increase of the effective consolidation stresses, and the compression index decreased with the increase of bentonite content. Meanwhile, the pore size distribution (PSD) curve of the backfill specimen almost turned into unimodal characteristics with only micropores distributed after consolidation. Additionally, the flow paths became more tortuous under compression which decreased the hydraulic conductivity. The montmorillonite aggregates in red clay-bentonite backfill formed into tortuous network structure which bound the clay aggregates together and effectively increased the tortuosity of flow paths.

Exploring the Influence of Chemical Conditions on Nanoparticle Graphene Oxide Adsorption onto Clay Minerals.

High concentrations of graphene oxide (GO), a nanoparticle substance with rapid manufacturing development, have the ability to penetrate the soil surface down to the mineral-rich subsurface layers. The destiny and distribution of such an unusual sort of nanomaterial in the environment must therefore be fully understood. However, the way the chemistry of solutions impacts GO nanoparticle adsorption on clay minerals is still unclear. Here, the adsorption of GO on clay minerals (e.g., bentonite and kaolinite) was tested under various chemical conditions (e.g., GO concentration, soil pH, and cation valence). Non-linear Langmuir and Freundlich models have been applied to describe the adsorption isotherm by comparing the amount of adsorbed GO nanoparticle to the concentration at the equilibrium of the solution. Our results showed fondness for GO in bentonite and kaolinite under similar conditions, but the GO nanoparticle adsorption with bentonite was superior to kaolinite, mainly due to its higher surface area and surface charge. We also found that increasing the ionic strength and decreasing the pH increased the adsorption of GO nanoparticles to bentonite and kaolinite, mainly due to the interaction between these clay minerals and GO nanoparticles' surface oxygen functional groups. Experimental data fit well to the non-linear pseudo-second-order kinetic model of Freundlich. The model of the Freundlich isotherm was more fitting at a lower pH and higher ionic strength in the bentonite soil while the lowest R2 value of the Freundlich model was recorded at a higher pH and lower ionic strength in the kaolinite soil. These results improve our understanding of GO behavior in soils by revealing environmental factors influencing GO nanoparticle movement and transmission towards groundwater.

The Chemical Compatibility of Sand–Attapulgite Cut-Off Walls for Landfills

Soil–bentonite cut-off walls have been widely used to control landfill pollution but they do not have good chemical compatibility with landfill leachate. Attapulgite can be substituted for bentonite in landfill cut-off walls. However, little is known about the chemical compatibility of attapulgite cut-off walls and leachate. This study experimentally investigated the chemical compatibility of attapulgite cut-off wall specimens with organic and inorganic contaminants and found that a sand–attapulgite cut-off wall has good chemical compatibility with organic contaminants. A CaCl2 solution was used to represent inorganic contaminants, and chemical oxygen demand (COD) was used as an indicator of organic content. The hydraulic conductivity of the cut-off wall initially decreased and then increased to become approximately constant as Ca2+ concentration increased. Changes in COD concentration were divided into a decreasing stage (0–10,000 mg/L) and a constant stage (10,000–40,000 mg/L). The increase or decrease in hydraulic conductivity was by no more than one order of magnitude. The increase in the hydraulic conductivity of the sand–attapulgite cut-off wall is explained in terms of bound water content and pore structure. An increase in Ca2+ concentration decreased the bound water content of the cut-off wall while the CaCl2 solution increased macropore and mesopore volume and decreased small pore volume in the sand–attapulgite cut-off wall. The purpose of this study was to elucidate the chemical compatibility of a sand–attapulgite cut-off wall with organic and inorganic contaminants and to increase the understanding of the interactions between the cut-off wall and the contaminants. The results of this research are informative for improving the application, design, and construction of sand–attapulgite cut-off walls.

Simulation study on inhibition performance of hydrate cellulose kinetic inhibitors for drilling in marine gas-bearing formations

In the marine high-pressure low-temperature environment, it is difficult to regulate the low-temperature rheology of the drilling fluid, and the spilled natural gas is easy to generate solid gas hydrate in the wellbore, causing problems such as wellbore blockage and increasing the risk of safe drilling operations. Although there are many researches on the invasion process of drilling fluid and the development of new hydrate inhibition, there is still a lack of research on the inhibition system suitable for drilling fluid. Therefore, this paper uses the self-developed hydrate formation evaluation experimental device to simulate and analyze the effect of inhibitors in reservoir environment and optimize the scheme of drilling fluid inhibition system. The results show that: (1) Through the improvement of the experimental device of water bath methane hydrate (MH) evaluation, the accuracy and parallel control of the equipment are enhanced, and the methane hydrate formed by sea water (SW) is less than that of distilled water (DW), and the structure of methane hydrate formed by distilled water is more compact. (2) Through the evaluation experiment of single inhibitor A3, PAC and CMC inhibition system, it was found that A3 had the best inhibition effect, and when the inhibitor concentration was 1.5 wt%, it had the best inhibition effect. (3) The influence of clay types on the formation of methane hydrate is also significantly different. Bentonite soil Red (BSR) has better inhibition performance than Bentonite soil Yellow (BSY), and its ' hut ' structure formed at low temperature is the reason for the formation of methane hydrate. (4) The inhibition ability of A3 inhibitor in BSY system and BSR system solution in general, the addition of KCl can play a strong synergistic inhibition ability with A3 in BSR system, and its electric field reduces the activation energy of water molecules as well as the consumption of free water is the reason to reduce the generation of methane hydrate.

Performance Evaluation of Clay Plastic Concrete of Cement and Epoxy Resin Composite as a Sustainable Construction Material in the Durability Process

In this research, bentonite soil was stabilized with cement and epoxy resin additives by gradually increasing the ratio of epoxy resin to water to withstand six successive wetting/drying (W/D) cycles. Unconfined compressive strength (UCS) tests were performed on the stabilized samples after curing and 24 h of soaking in the third and sixth cycles. The swelling–shrinkage potential of bentonite soil was evaluated indirectly by analyzing its stress–strain behavior. The results showed that for different amounts of cement, the minimum ratio of epoxy resin to water added to bentonite soil to last up to six cycles was equal to 1:1. Also, by stabilizing the bentonite soil so that the total weight of the optimum moisture content was replaced with epoxy resin, the strength and rigidity attained the level of normal concrete, with the difference that the ductility was much more significant. The failure strain value increased by 32 times, and the plastic region of the stress–strain curve expanded over the wide strain interval with a length of about 5%. Clay plastic concrete design consisting of cement and epoxy resin develops sustainable ground improvement methods.

Assessment of engineering properties of slag mixtures as a bottom liner in landfills

This work examines the engineering properties and leachate characteristics of ground granulated blast-furnace slag (GGBS) blended with laterite soil–bentonite mixtures as a bottom landfill liner. In this study, laterite soil is considered a non-expansive and non-plastic clay; in contrast, bentonite is a highly expansive and highly plastic clay. Laboratory experiments were performed to quantify the effect of GGBS–laterite soil–bentonite mixtures on the liquid limit (LL), free swell index (FSI), compaction characteristics, unconfined compressive strength (UCS), hydraulic conductivity (k) and leachate characteristics tests. As the GGBS percentage in the mix blend increased, the LL, FSI, optimum moisture content, k determined with deionised water/diesel oil contaminants and leachate concentration decreased, whereas the maximum dry densities and UCS value increased. Furthermore, X-ray diffraction analysis and energy-dispersive X-ray spectroscopy were performed on UCS samples to determine the occurrence of a hydration reaction in mix blends at 0, 14 and 28 days of curing. The test results revealed that an increase in the calcium (Ca)/silicon (Si) ratio and a decrease in the aluminium (Al)/calcium ratio enhanced the UCS during the curing period. Consequently, 20% GGBS combined with laterite soil–bentonite mixes proved to be the ideal material for landfill bottom liners in waste containment systems.

Analytical Solution of the One-Dimensional Transport of Ionic Contaminants in Porous Media with Time-Varying Velocity

The one-dimensional convection–dispersion equation has been widely used to describe the migration process of contaminant leachate through barriers. However, most of the existing solutions are limited to simple conditions. In this study, a one-dimensional convection–dispersion model with time-dependent velocity was established while considering the change in the permeability coefficient. The analytical solution of the model was obtained by using the integral transformation method. Based on the analytical model, three special conditions were assumed for comparison. The results showed that the concentration levels of pollutants inside the barrier would significantly increase with the increase in the flow velocity, and the pollutant concentrations inside the barrier would be increased by four times compared with the normal flow velocity when the flow rate increased by two times. The transports of heavy metal ions with variable velocities through soil–bentonite and soil–attapulgite barriers were predicted under field conditions. The predicted results showed that the breakthrough time would be reduced by as much as two times. In engineering practice, a barrier’s service performance can be improved by controlling the temperature of the seepage field and improving the chemical compatibility of the barrier materials.