Soil-bentonite Mixtures Research Articles

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

Transport of Organic Contaminants in Composite Vertical Cut-Off Wall with Defective HDPE Geomembrane.

Soil-bentonite vertical cut-off wall is an emergency technique used for contaminant control in geo-environmental engineering, high-density polyethylene (HDPE) geomembrane (GM) with an extremely low-permeability coefficient is expected to enhance the contaminant barrier effect of the vertical cut-off wall. To evaluate the barrier performance of the composite barrier composed of GM and soil-bentonite mixture towards organic contaminant, while also quantitively revealing the impact of GM defects and placement, a one-dimensional transport model for organic contaminants in composite barrier is solved under semi-infinite boundary conditions. The proposed transport model is validated by numerical simulations using COMSOL Multiphysics 5.4, and the effects of GM defect rate, placement within the composite isolation wall, and contact level with soil-bentonite on contaminant transport behavior are further studied. The results show that as the average frequency of GM defects increases from 2.5 to 50 holes per hectare, the breakthrough time of organic contaminants through composite barrier decreases by almost 70%. Poor contact level between GM and soil-bentonite mixture may reduce the breakthrough time of the composite cut-off wall by 65%. Although the selection of GM placement has limited impact on the transient flux of contaminants, it does affect the total flux of contaminants over a certain period of time. The effects of permeability coefficient, effective diffusion coefficient, distribution coefficient, and hydraulic head of the composite cut-off wall can be considered by the proposed analytical solution, which would provide guidance and reference for the design and service performance evaluation of the composite cut-off wall.

Hydraulic Conductivity of Unsaturated Specimens of Lateritic Soil-Bentonite Mixtures

Hydraulic Conductivity of Unsaturated Specimens of Lateritic Soil-Bentonite Mixtures

Evaluation of red soil-bentonite mixtures for compacted clay liners

Compacted clay liners are an integral part of the waste landfills, which are provided to contain the leachate within the landfills and protect the surrounding environment. Generally, locally available natural soils are used for the construction of compacted clay liners if they satisfy the design criteria. However, not all soils in their natural state satisfy all the design criteria for the liner materials. Thus, there is a definite need to modify the locally available natural soils by blending with bentonite to meet the required design criteria for the liners. In view of this, the present study evaluates the suitability of an Indian red soil enhanced with bentonite as a liner material. To achieve this, a series of experiments were carried out using locally available red soil and bentonite. First, the suitability of the red soil was evaluated as a liner material. The experimental results showed that the red soil met all the selection criteria stipulated by the Environmental Protection Agencies (EPAs) for the liners except the hydraulic conductivity criterion. Therefore, the red soil was mixed with bentonite contents of 10%, 20% and 30%, and the red soil-bentonite mixtures were evaluated for their suitability for liners in their compacted state. Further, as the liners in the arid and semi-arid regions are subjected to moisture variations due to seasonal moisture fluctuations and other factors, the red soil-bentonite mixtures were subjected to wet-dry cycles, and their suitability was evaluated after wet-dry cycles. The experimental results revealed that all the red soil-bentonite mixtures met the stipulated EPA criteria for the liners in the as-compacted state. However, the red soil-bentonite mixtures with 20% and 30% bentonite contents only satisfied the hydraulic conductivity requirement even after wet-dry cycles. The experimental findings were supplemented with the microstructural insights captured through digital camera images, scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) studies.

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.

Laboratory investigation on the retention performance of a soil-bentonite mixture used as an engineered barrier: insight into the effects of ionic strength and associated heavy metal ions.

Soil-bentonite (S-B) materials are promising backfill materials for use as engineered barriers in heavy metal-contaminated sites. The effects of contaminant exposure on the retention performance of the S-B barrier remain unrevealed. In this study, based on the pollution status of an abandoned ferroalloy factory located in southern China, the retention performance of the S-B mixture toward Cr(VI) and Zn(II) was studied through adsorption and diffusion experiments sequentially; the separate effect of ionic strength (binary solution) and the combined effect of ionic strength and associated heavy metal ion (ternary solution) were discussed. In NaCl-Cr(VI)/Zn(II) binary solutions, the adsorption of Zn(II) onto the S-B mixture is larger than that of Cr(VI). Kd, Qmax, and ɛacc (accessible porosity) of Cr(VI) increase through increasing ionic strength, while Zn(II) shows the opposite trend; De (effective diffusion coefficient) values for both Cr(VI) and Zn(II) increased with increasing ionic strength and follow a sequence of Cr(VI) > Zn(II), indicating a better retention performance of the S-B mixture to Zn(II). For a given ionic strength, the adsorption of Zn(II) was larger than that of Cr(VI), which can be attributed to the retention specificity of the S-B mixture to anion and cation. In Cr(VI)-Zn(II)-NaCl ternary solutions, the adsorptions of Cr(VI) and Zn(II) are enhanced in varying degrees when compared with their binary solution, which probably could be attributed to the ion bridge role of Cr(VI)/Zn(II) to connect each other that relatively increased the adsorption capacity of S-B material. This work will contribute to an in-depth understanding of the retention performance of the S-B mixture in complicated chemical environments and facilitate the selection of future remediation strategies.

Experimental Study on Electrical Resistivity Characteristics of Saturated Sand Mixes with Bentonite Slurry

Bentonite slurry is widely used in underground and geotechnical engineering because of its strong ability of wall protection. Slurry penetration, which is of great significance for the soil stability, is difficult to observe directly during the soil and slurry interaction. Slurry penetration would change the electrical resistivity of soil, which provides an indirect method to monitor the degree of slurry penetration. This paper aimed to investigate the electrical resistivity characteristics of soil-bentonite mixtures. Several test groups with different material components were carried out. The effects of some factors including water environment, CMC (carboxymethyl cellulose) contents, soil particle gradation, and electrode distance on the electrical resistivity of slurry-soil mixtures were studied and the relationship between soil electrical resistivity and slurry concentration was established. The results in this paper can provide references for the application of the electrical method on slurry penetration.

Permeability of soil-bentonite cut-off wall backfill material

The effects of bentonite content on permeability, porosity and bound water of soil-bentonite mixtures were evaluated using the improved flexible wall test and the moisture centrifugal dewatering test with three different bentonites from China. The results showed that when backfills were formed by mixing bentonite and sand, there was a critical bentonite content of the lowest porosity. If the bentonite content was below this critical content level, permeability decreased rapidly, whereas if the bentonite content was above this critical level, permeability decreased slowly. Moreover, when the bentonite content increased, the bound water percentage of the mixtures constantly increased. Assuming that the bound water surrounded the bentonite particles, an approximate calculation method of the effective porosity was proposed.

Applicability of Recycled Soil Mixed with Bentonite and Polymer as a Waste Landfill Liner

Waste landfill liner has been developed with a variety of materials, but the landfill liner and cover material have not been developed in consideration of the local conditions. In order to build a cost effective municipal solid waste (MSW) landfill site, it is necessary to develop technology that utilizes materials suitable for local characteristics as liner. The purpose of this study is to develop an amended compacted clay liner (CCL) by proportionally mixing construction waste soil called “recycled soil” with small amount bentonite powder as well as polymer powder. Permeability and strength characteristics of recycled soil-bentonite mixture were analyzed through laboratory test and then compare this mixture with characteristics of marine clay-bentonite mixture. The characteristics of strength and permeability were analyzed by applying different mixing ratios with adjustment of polymer and bentonite ratios in consideration of its proportion of bentonite’s weight to improve economic efficiency and increase the strength of recycled soil-bentonite mixture. Finally, the proper mixing ratio of recycled soil-4% bentonite-0.28% polymer mixture was determined considering economical efficiency. The mixture was confirmed to be suitable as lining material based on the results of dry shrinkage test, free swelling test, and soil contamination test. In this study, it is proposed the mixing ratio of recycled soil, bentonite, and polymer as a minimum ratio that satisfies the standard of hydraulic conductivity(1 × 10−7 cm/sec) on the waste management law and unconfined compressive strength (500 kPa) on the specification of construction of waste landfill liner.

Swell-shrink and hydraulic behaviour of compacted red soil-bentonite mixture

Clay liners are provided in waste landfills to prevent the leachate from percolating into underlying soil and ground water and polluting it. Hence, soils used as landfill liners must possess low hydraulic conductivity (< 10−7 cm/s). In the initial as-compacted state, liners satisfy this design criterion. However, in the field, liners are subjected to alternate wet-dry cycles and the initial microstructure of liners change, thereby affecting their hydraulic properties. The present study was conducted on a locally available red soil mixed with bentonite so that it satisfies the requirement of hydraulic conductivity in the as-compacted state. To achieve this objective, identical specimens compacted at optimum moisture content to its maximum dry density were inundated with distilled water under a surcharge load of 12.5 kPa. Upon attainment of maximum swelling, hydraulic conductivity tests were conducted at swollen state under a hydraulic gradient of 20. The soil specimens were then dried at a temperature of 45±2 °C. The weight, height and diameter of specimens were measured continuously during drying to study the shrinkage behaviour of the soil. The dried specimens were subjected to subsequent wet-dry cycles until the specimens reached an equilibrium state and the hydraulic conductivity was determined after each wetting cycle. SEM images were also captured to analyse the changes in the soil structure in the as-compacted state and at the end of different wetting cycles.

Fate of bentonite in slag–cement–bentonite slurry trench cut-off walls for polluted sites

Soil–bentonite (SB) and slag–cement–bentonite (slag-CB) slurry trench cut-off walls are widely used low-permeability subsurface barriers against groundwater or contaminants. The bentonite in SB walls is instrumental to the performance of the barrier. However, when mixed with Portland cement and slag in slag-CB walls, bentonite participates in ‘secondary’ chemical reactions throughout cement hydration. Using mineralogical methods, the goals of this paper are to examine the fate of bentonite in slag-CB mixtures and to discuss the implications of the associated chemical reactions for the slag-CB wall performance. Laboratory-prepared mixtures of dry and hydrated slag-CB were analysed using X-ray diffraction over 3 months to investigate the evolution of mixtures during curing. Results confirm that bentonite clay minerals dissolve in slag-CB slurries and that bentonite is virtually absent in the hardened slag-CB material. Furthermore, carbonation and pozzolanic chemical reactions also take place on slag-CB hydration and curing, which form secondary minerals over time. Hence, unlike SB mixtures, the bentonite in slag-CB mixtures no longer retains its original crystalline structure, as it participates chemically in hydration processes, although it becomes a precursor of pozzolanic products. Nonetheless, bentonite is instrumental to the workability and initial set of the mixture. It is concluded that the concepts of compatibility traditionally accepted for SB walls are inappropriate for slag-CB walls. Possible implications include that due to the onset of carbonation, the barrier could degrade if the contaminants are acidic; also, the formation of pozzolanic hydrates may improve the contaminant sorption properties of the barrier.

Effects of Compaction Condition on Shear Strength of Soaked Soil-bentonite Mixture

Effects of Compaction Condition on Shear Strength of Soaked Soil-bentonite Mixture

Proportion Test Results of Soil-Bentonite Mixture and Cement Stabilized Soil Using the Crushed Stone Dust (Screenings) for the Surface Impermeable Soil Liner Material

Crushed stone dust is stone powder generated in the production process of crushed stone, and crushed stone dust prepared to a maximum particle size of 2.5 mm or less is specified as "Screenings (F-2.5)" by JIS A 5001 (Crushed Stone for Road Construction). "Screenings" is mainly used as a fine aggregate of asphalt concrete for paving. Since "Screenings (F-2.5)" is a product of the stone crushing factory, the quality is relatively stable, and the fine particle fraction (75 µm or less) is also contained at about 0 to 20%, and therefore, the applicability as soil material is considered to be high. In the preliminary study, we investigated the applicability of "Screenings (F-2.5)" as base material for the surface impermeable soil liner material (soil-bentonite mixture and cement stabilized soil), and we got a suggestion that the target water permeability could be achieved by appropriately setting the types and amounts of bentonite and cement-based materials when the target compaction degree was set to Dc 95 % or more and the target water permeability coefficient in laboratory test was set to 1×10-7 cm/s or less (1×10-9 m/s or less) . In this paper, we introduce the result of proportion test carried out for the purpose of actually applying soil-bentonite mixture and cement stabilized soil using crushed stone dust (Screenings) as a base material to surface impermeable soil liner construction work.

Geotechnical Properties of Salak Tinggi Residual Soil-Bentonite Mixture as Liner

This paper intends to present an experimental study on the effectiveness of using bentonite mixed with originating sedimentary residual soil as a liner. In order to investigate the effectiveness of soil-bentonite mixture, several tests were performed on Salak Tinggi sedimentary residual soil mixed with different percentage of bentonite content such as 5%, 10% and 15%. The laboratory testing was performed on the mixed sample consist of physical properties of the soil such as: pH, plastic limit (PL), liquid limit (LL), plasticity index (PI), linear shrinkage (LS) and specific gravity (SG). Meanwhile, the compaction testing was performed such as Bristish Standard Light (BSL) and Bristish Standard Heavy (BSH). The compaction test was conducted to determine the maximum dry density (MDD) and optimum moisture content (OMC) at two different compaction energies. The result showed that the addition of bentonite on the Salak Tinggi residual soil can change and improve the physical properties of the results. Moreover, the results of compaction show a decrease in the MDD value for any increase in the percentage of bentonite mixture at all energies. However, MDD value increases with increasing of compaction energy used in soil–bentonite mixture. All these changes improved the performance of residual soil use as liner purposes.

Comparative Study of Behaviour of Soil and Soil-Bentonite Mixtures for The Construction of Impermeable Barriers

Comparative Study of Behaviour of Soil and Soil-Bentonite Mixtures for The Construction of Impermeable Barriers

Compressibilidade em misturas de solo laterítico, bentonita e fibras para uso em barreiras de fluxo

Os solos lateríticos devido à sua elevada resistência mecânica quando compactados, os solos lateríticos possuem potencial aplicabilidade em obras geotécnicas, inclusive em barreiras de fluxos, tais como liners em aterros sanitários, cut-off de barragens, e cut-off walls para contenção de plumas contaminantes. Neste caso, também são requeridos baixa condutividade hidráulica e compatibilidade com os fluidos circundantes, sendo a adição de bentonita a alternativa usualmente empregada para a diminuição da condutividade hidráulica e aumento da capacidade sorciva. Por outro lado, a bentonita pode aumentar a compressibilidade dos solos, deformando-o e comprometendo a integridade da barreira de fluxo. Este artigo apresenta os resultados de compressibilidade em misturas de um solo laterítico, bentonita e fibras. Foram testadas amostras de solo laterítico, mistura contendo solo laterítico e 5% de bentonita e mistura contendo solo laterítico, 5% de bentonita e 1% de fibras de polipropileno. Os ensaios englobaram caracterização mineralógica do solo laterítico e da bentonita, avaliação das propriedades geotécnicas e avaliação de compressibilidade em célula de adensamento com 5 estágios de carregamento. De forma geral, os resultados demonstraram aumento da plasticidade e da compressibilidade no solo laterítico devido à adição de bentonita. Por outro lado, a adição de fibras de polipropileno à mistura solo-bentonita não resultou em diminuição da compressibilidade, demonstrando ineficiência da aplicação de fibras de polipropileno para o uso em barreiras de fluxo.

Prediction of hydraulic conductivity for soil–bentonite mixture

Owing to its low hydraulic conductivity, soil and bentonite mixture is applied as a liner material. However, the experimental determination of hydraulic conductivity, which is controlled by various physical, chemical and mineralogical factors, requires an expensive and time-consuming setup. In the present work, multigene symbolic, genetic programming was used to model functional relationships for hydraulic conductivity. The developed model was able to generalize highly nonlinear variations in data as well as predict system behavior from experimental observations. It was found that the predictions obtained from developed model agree well with experimental observations.

Performance enhancement of sand–bentonite mixture due to addition of fiber and geosynthetic clay liner

In the absence of impermeable natural soils, compacted sand–bentonite mixture along with a layer of geosynthetic clay liner (GCL) is used as a liner material at the waste disposal site. However, due to desiccation, the bentonite present in the liner shrinks resulting in an increase in the hydraulic conductivity of the liner. To prevent the desiccation cracking of bentonite, glass fibre is added to the mixture as a reinforcing material. However, the addition of the fibre can influence the geotechnical properties of liner material. To study the effect of the fibre on the geotechnical properties of the sand–bentonite mixtures with one layer of GCL, glass fibre of 10 mm length was added in the proportion of 0.5 and 1.0% to different sand–bentonite mixtures. Result shows that the swelling pressure and swelling potential of the soil–bentonite mixture with a layer of GCL decreased significantly with the increase in the glass fibre content in the mixture. The hydraulic conductivity of the mixtures was decreased with the inclusion of the GCL to mixtures; however, it increased considerably when glass fibre was added to the mixture. The compression index of the mixtures with GCL decreased marginally due to the inclusion of fibre.

Influence of freeze–thaw cycles on the performance of covers with capillary barrier effects made of crushed rock–bentonite mixtures to control oxygen migration

In temperate climates, covers with capillary barrier effects (CCBEs) are being used successfully to prevent oxygen fluxes from reaching covered potentially acid mine drainage (AMD) generating mine tailings. In northern climates, the more attractive option for mine site reclamation is insulation covers, which are designed to keep reactive materials frozen. This article suggests that CCBEs can simultaneously control oxygen migration and mine waste temperature to inhibit AMD generation. However, in northern conditions, where natural fine-grained materials needed for the CCBE moisture-retaining layer are not always available, soil–bentonite mixtures could be used instead. This laboratory study assessed — using instrumented columns — the effects of freeze–thaw cycles on the performance of three CCBEs made with crushed rock–bentonite mixtures. An oxygen diffusion test was developed to determine the effective diffusion coefficient of oxygen (De) and its sensitivity to freeze–thaw cycles. The results show good initial performance for the saturated CCBEs. However, the tested CCBEs are significantly affected by freeze–thaw cycles and have limited oxygen-limiting ability.