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Enhancing the dynamic properties of expansive soils using cementitious materials has attracted the attention of many researchers over the past few decades. Supplementary cementitious materials (SCMs) can be used as partial substitutes for cement owing to their pozzolanic activity that further improves the mechanical performance of cement-stabilized soils upon curing. In this study, the effect of cement and zeolite incorporation on the mechanical behavior of expansive clay was quantified using the pressure wave velocity (Vp) indicator obtained from ultrasonic pulse velocity tests performed at different curing times. Furthermore, a polynomial model was developed to establish the relationship between Vp and zeolite replacement levels at specific curing times and cement contents. The results show that a polynomial function captured the decreasing trend of Vp upon the increase in zeolite at curing times below 14 days. Additionally, the developed equation explained the upward trend of Vp owing to the pozzolanic activity of zeolite at later curing times with an accuracy of over 92%. The coefficients of the polynomial model also increased with the increment of the cement percentage which conformed to the consecutive rise in Vp. Ultimately, the polynomial coefficients were expressed in terms of cement content and curing time using the Volterra series. Using this model, the optimum percentage of cement replaced with zeolite (Zopt), the efficiency of using Zopt instead of cement, and the percentage of zeolite replacement to achieve equivalent Vp of cemented clay samples (ZC) were estimated. The findings of this study contribute to promoting geotechnical sustainability by replacing cement with zeolite that has a considerably lower environmental footprint. Clay is a type of soil that can be found in many construction projects. For instance, many roads and buildings' foundations are constructed on clay soils. To ensure the necessary strength of the clay under the main structure, the soil should often be stabilized using adhesive construction materials such as cement. Interestingly, a portion of the cement could be replaced with other minerals not only to improve engineering performance but also to promote sustainability by lowering cement consumption. In this study, the effect of zeolite as a partial replacement for cement on the strength of clay soils was experimentally evaluated. The effect of various design parameters, such as cement replacement level and curing time, on the stability of clays was investigated using an advanced technique called the ultrasonic pulse velocity (UPV) test. Furthermore, a simple mathematical model was proposed based on the experimental results to help engineers design the stabilization plan and timely decide about the next steps of the construction process. [ABSTRACT FROM AUTHOR]

This investigation examines the effect of clamshell ash (CSA) and lime additives on the physico-mechanical characteristics of kaolinite clay soil stabilized at the optimum silica fume content. Laboratory tests were performed to assess plasticity, shrink-swell characteristics, compaction characteristics, unconfined compressive strength (UCS), shear strength characteristics, mineralogical and morphological microstructure characteristics of stabilized soil specimens. The kaolinite clay soil was stabilized at its optimum silica fume content (6%) to produce the highest strength and was altered with three non-identical proportions of clamshell ash and lime (3%-9%). Cylindrical soil specimens, 76 mm in height and 38 mm in diameter, were moulded and treated for curing periods of 1, 7, 14, and 30 days to examine the strength of the altered soil. The findings revealed that, adding clamshell ash and lime significantly alters the plasticity, shrink-swell, maximum dry unit weights, and optimum moisture contents of the silica fume-stabilized soil. In terms of strength, the beneficial effects of CSA and lime additives were found to be more significant with more extended curing periods. Incremental increases in curing periods resulted in further enhancements in UCS, cohesion, and internal friction angle, indicating continued strength development over time. Microstructural analysis using field emission scanning electron microscopy and X-ray diffraction provided insights into the interparticle bonding mechanisms and microstructural changes induced by the addition of CSA and lime. The emergence of cementitious phases and pozzolanic responses between soil particles and stabilizers contributed to the densification and strengthening of the stabilized soil matrix. The findings of this study provide valuable insights into the potential of clamshell ash and lime additives to enhance the engineering properties of kaolinite clay soil stabilized with silica fume. These results have implications for sustainable soil stabilization practices, offering a promising approach to improve the performance of soils for various engineering applications, including construction and geotechnical projects. [ABSTRACT FROM AUTHOR]

Construction of earth fill dams offers a cost-effective solution for various purposes. However, their susceptibility to internal soil erosion, known as piping, poses a significant risk of structural failure and resultant loss of life and property. Soil stabilization emerges as a practical technique to fortify these dams against such threats. This study investigated the impact of lime on the internal erosion properties of clay soils, focusing on CH and ML soil types. Specimens of different lime content were prepared and remolded at 95% relative compaction and optimum moisture content. Hole Erosion tests at varying lime concentrations and curing durations were adapted to conduct the investigation. This investigation aims to optimize lime content and curing time for cohesive soil stabilization against internal erosion. Findings revealed that 2% and 5% of quicklime, by dry weight of the soil, effectively stabilized CH and ML soils, respectively, against internal erosion, with a two-day curing period proving optimal. Furthermore, the addition of lime significantly enhanced erosion rate index and critical shear strength in clay soil, underscoring its efficacy in soil stabilization efforts. [ABSTRACT FROM AUTHOR]

The technique of mass soil stabilization using alternative binders to Portland cement (PC) has been used successfully in the past. However, knowledge gaps exist regarding the design of these binders. Ground-granulated blast furnace slag (GGBS) has been widely used as a substitute for PC; however, it requires an alkaline activator (e.g. lime and PC) to promote pozzolanic reaction and strength enhancement. A candidate that presents a less energy-intensive manufacturing and carbon footprint is carbide lime (CL), a by-product of acetylene gas production, rich in Ca(OH)2. The main problem with the pozzolanic binder in the stabilization technique is its slow reaction kinetics and the long time required for laboratory-scale investigations before in situ application. Therefore, this research presents a dosing study of a ternary binder (TB) comprising CL, GGBS and PC type III (CEM-III) to mass-stabilize a clayey organic soil using thermal curing as an innovative technique to improve the feasibility of laboratory-scale investigations. The effects of binder composition and thermal curing time on the evolution of strength, stiffness, mineralogy, and microstructure were determined. The results, supported by a statistical analysis (ANOVA) and by a multivariate regression analysis (MRA), have shown that the new TB produced a superior mechanical response to soil samples stabilized exclusively with CEM-III. This was evidenced by a less porous microstructure (more reaction products) and mainly the formation of a C–A–S–H gel, as a product of CEM-III hydration and alkaline activation of GGBS (blended cement), whereby the CL content played a key role for the development of the long-term pozzolanic reaction. [ABSTRACT FROM AUTHOR]

This study investigates the stabilization performance of clayey soil treated with alkali-activated hybrid slag/cement. Sodium silicate (SS) and sodium hydroxide (SH) are used as alkali activators, whereas ground blast furnace slag (GGBS) and ordinary Portland cement (OPC) are used as sources of aluminosilicate. A total of 27 different types of mixtures are used for stabilization. Unconfined compressive strength (UCS) of untreated clay and stabilized soils are performed at immediately, 3-, 7-, 28-, and 90 days curing times under air-dried and wet-cured conditions. In addition, 90-d volume and mass changes in the samples are measured. Stabilized samples with an SS/SH ratio of 1 under air-dried conditions reveal moistening at early curing ages (=28 days); afterward, sodium carbonate crystals appear in these samples at longer curing ages. Geopolymer-treated clayey soil exhibits lower volumetric and mass changes compared with OPC. Most of the stabilized clayey soil with alkali-activated hybrid slag/cement exhibits higher strength compared with OPC under air-dried and wet-cured conditions. [ABSTRACT FROM AUTHOR]

The use of lime in sulfate-bearing clayey soils has historically caused structural damage to infrastructures due to the formation of an expansive ettringite mineral. In this paper, a research was conducted to study the effectiveness of natural pozzolana (NP) for providing better stabilization of sulfate-bearing soils. Compaction and free-swell potential tests were first performed on lime-stabilized grey and red clayey soils (GS and RS) containing different contents of added sodium and calcium sulfates (2, 4 and 6% Na2SO4 or CaSO4⋅2H2O). Then, the same tests were repeated by adding 20%NP. The test results indicated that the presence of 4% and 6% Na2SO4 in the soil resulted in an abnormal increase in the swell potential of both lime-stabilized GS and RS. The X-ray diffraction (XRD) results confirmed the growth of the ettringite mineral responsible for this higher swell potential. However, the use of 8% lime with 20%NP in stabilizing sulfate-bearing clayey soils produced significant improvements in the optimum moisture content (OMC) and maximum dry density (MDD), as well as in the swell potential. The addition of 20%NP into the lime-stabilized GS and RS eliminated the harmful effect of Na2SO4. In addition, for 120-day curing period, the use of 6% CaSO4⋅2H2O was found very effective by reducing the swell potential of NP-lime-stabilized GS and RS from 7.33% to 0.4% and from 2.79% to 0.2%, respectively trips. [ABSTRACT FROM AUTHOR]

New ways to apply sustainable materials, such as biomass components, are essential for reducing dependence on fossil fuels. This work investigated the engineering properties of unsaturated expansive subgrade soils stabilized by bio-based energy coproducts containing lignin. Lignin is a waste by-product of the paper and pulp industry that is frequently burned. Highway subgrade could consume lignin as an environmentally benign, low-cost, and energy-efficient chemical substance for soil stabilization. Swell and shrink behavior of expansive subgrade soils complicates highway construction and causes damage to existing highways. However, research on the hydromechanical properties and volume change behavior of lignin-stabilized expansive soil is limited, and better insight is required into its unsaturated behavior for safe and economical pavement design practices. In this research, a series of geotechnical laboratory tests were conducted to characterize expansive subgrade soils treated with lignin by determining the Atterberg limits, compaction and consolidation behaviors, swelling characteristics, and water retention properties. The mechanisms influencing the changes in engineering properties of lignin-treated expansive soils were further investigated using soil pH, scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy analysis. The study shows that the optimal lignin content contributed to an acceptable degree of soil stabilization. The lignin-based cementing material effectively bonds soil particles together and fills pores, thereby preventing water infiltration into the soil and reducing the swell–shrink potential of stabilized soils. [ABSTRACT FROM AUTHOR]

Expansive soils are extremely susceptible to swelling and shrinkage associated with seasonal changes in their moisture content. This can cause serious damage to structures constructed on expansive soils. Stabilization using additives is widely used to mitigate the concerns of expansive soils by controlling the changes in volume, thereby increasing the strength and durability of the soils. Multistabilizers, including a low percentage of conventional additives with nonconventional additives, can reduce the costs of stabilization. The performance of the stabilized soil can be enhanced by admixture optimization to ascertain that the agent's ratios are quite adequate to meet the optimal levels of modification. Unfortunately, despite the development of advanced techniques for investigating the stabilization of expansive soil, limited studies are devoted to the optimization of admixture to soils. Hence, in this research, an approach based on rough set theory, a mathematical data mining approach, is presented for multiagent optimization for efficient treatment of expansive soils. The multiadditives used in this study are almond shell ash (ASA), volcanic rock dust (VRD), and portland cement (PC). The differential free swell test, the California bearing ratio test, and the unconfined compressive strength test were applied for assessing the characteristics of the stabilized soil specimens. The obtained results and the confirmatory tests demonstrated that a combination of 20% ASA and 20% VRD with 8% PC provides the optimum results in the properties of expansive soil. The microstructural analysis denoted an enhanced modification of the soil engineering properties. The outcomes of this research confirm that the rough set optimization procedure is highly suitable for application in multiagent optimization for the efficient treatment of expansive soils. [ABSTRACT FROM AUTHOR]

The low bearing capacity of expansive soils often results in serviceability issues and premature failures of infrastructure built upon them. Various studies have demonstrated the use of different soil treatment methods using mechanical or chemical approaches to stabilize the weak ground as a precaution. Most of the reported studies are limited to either lab-based investigations or field monitoring works without the scientific connection between theory and translation. This study aims to verify the field application of a novel soil stabilization method by conducting laboratory-controlled experiments and field performance testing as verification. Enzyme–based soil stabilization was adopted for in-situ clay soil in combination with ordinary portland cement as a sustainable stabilization approach. Soil samples were collected at different regions from the field to evaluate the effectiveness and the mechanism of soil stabilization in the field by the means of replicating stabilization at the laboratory scale using identical mixing proportions of the additives. The mechanical behavior of stabilized soil was assessed through the unconfined compression strength and California bearing ratio test methods. In addition, the changes in the chemical composition of the soil due to the additives were evaluated through the X-ray diffraction testing technique and microporosity test using 2D images translated to 3D profiles from X-ray micro CT tomography. The efficacy of field stabilization was evaluated by conducting the falling weight deflectometer test in the stabilized site. Results from the study are useful to understand the efficacy of field soil stabilization and enhance the reliability of enzyme–based stabilization in practice. [ABSTRACT FROM AUTHOR]

The present work aims to evaluate expansive soil stabilization using different additives. Twenty soil mixtures consisting of 10%, 20%, 25%, and 30% zeolitic tuff (ZT) with 2%, 4%, and 6% lime in various combinations were used to stabilize the soil for pavement subbase application. A comprehensive test program, including Atterberg's limits, compaction, unconfined compression strength (UCS), California Bearing Ratio (CBR), resilient modulus, and permanent deformation, was performed on natural and stabilized soil specimens. Scanning electron microscopy (SEM) supplied with energy-dispersive X-ray spectroscopy (SEM/EDX) was used to confirm the study findings. Adding ZT increases the availability of the silica and alumina needed for the pozzolanic reaction; test results revealed that adding ZT increases the maximum dry unit weight, CBR, UCS, resilient modulus, decreases plasticity, and permanent deformation. As such, ZT can improve the physical and mechanical properties of lime-stabilized soil as a pavement's subgrade and subbase layers. [ABSTRACT FROM AUTHOR]

Soft clay soils are in many coastal areas, these soils generally have high compressibility and don't provide required bearing capacity. Various techniques are used to improve these soils. The stone column technique has been successfully applied for the ground improvement. A stone columns technique is one of the soil stabilization methods that is used to increase strength, decrease the compressibility of soft and loose fine graded soils, accelerate a consolidation effect, and reduce the liquefaction potential of soils. They are mainly used for stabilization soft soil such as soft clays, silts, and silty sand. Several research has been conducted on the behavior and performance of stone columns with various materials utilized as column filler replacing the normal aggregate. This paper will review extensively on previously conducted research on some of the materials used as stone column backfill materials, its suitability, and the effectiveness as a substitute for regular aggregates in soft soil improvement works. This paper also discusses the techniques and methods of construction of stone columns. The bearing capacity of stone columns, and a combination of both methods in reinforced and unreinforced modes are presented using scaled physical models. The effect of various diameters with various depths in ground also reviewed. Results show that using stone column improves bearing capacity of soft soils and decreasing settlement. Using geotextile as stonecolumn encasement increases the efficiency of stone columns significantly. Finally, some guidance and recommendations are provided on parameter selection for the study of stone columns. [ABSTRACT FROM AUTHOR]

This research evaluates the changes brought about by the addition of asphalt emulsion and steel filings in clayey soils for subgrade in urban pavements. For this study, different dosages of each additive were established, being 1%, 2%, 4%, 8%, and 15% for the steel filings and 3%, 6%, 9%, 13%, and 18% for the asphalt emulsion, obtaining favorable results in the subgrade in accordance with the CE.010 Urban Pavement standard. With the steel filings the CBR (California Bearing Ratio) had a linear increase whose maximum value was reached with the dosage of 15% increasing the CBR considerably by 189.47% above the CBR of the natural soil; on the other hand, with the asphalt emulsion a maximum increase in CBR was obtained with the dosage of 13% obtaining an increase of 236.84% and after that a decrease is observed with the addition of 18% of asphalt emulsion. [ABSTRACT FROM AUTHOR]

The main thrust of this research was to establish any benefits of mellowing, and the optimal moisture content (OMC) for compacting mellowed sulphate-bearing clay soil undergoing the stabilization process. Two three-day mellowing regimes were carried out, prior to final compaction, at different initial moisture contents of 30% or 40% OMC. The unmellowed specimens were compacted immediately after mixing with the blended stabilizers. A blend of quicklime (L) with a sustainable by-product, silica fume (SF), at a 1:1 ratio (2%L–2%SF) was used. Linear expansion and unconfined compressive strength (UCS) tests were carried out to evaluate the benefits of mellowing. The test results suggested that the mellowed test specimens achieved better UCS and swelling properties compared to the unmellowed specimens. Mellowing at 1.2 OMC produced better strength performance than at 1.4 OMC, whereas mellowed specimens at 1.4 OMC showed better resistance to linear expansion compared to 1.2 OMC. The research findings suggested that optimal performance was achieved by mellowing at the higher initial moisture condition of 40% OMC and compacting the materials at the lower moisture condition of 1.2 OMC. [ABSTRACT FROM AUTHOR]

Singapore has a relatively high water table. When liquefied natural gas (LNG) storage systems are built in soils below the water table in Singapore, the engineering properties of the surrounding soils could be improved through cement stabilization. Due to the extremely low temperature (T) of LNG (approximately −162°C), the effect of ultralow T on the physical and mechanical properties of cement-stabilized soil in case of accidental LNG leakage should be investigated. However, existing studies on cement-stabilized soils are limited to T above −20°C. Therefore, in this study laboratory experiments to quantify volumetric expansion, unconfined compressive strength (UCS), and Young's modulus (E) of cement-stabilized soils at −40°C, −80°C, and −120°C were conducted. The experimental results indicated that the stabilized soils' volumetric expansion reached ≤2.6% at −120°C. The UCS and E of the stabilized soils increased from 0.9 to 27.6 MPa and from 99.8 to 2,669 MPa, respectively, and the T decreased from 24°C to −120°C. In summary, the ultralow T induced limited volumetric expansion (<3%) for cement-stabilized soil and significantly increased its strength and E, which indicated that cement soil stabilization could be beneficial for underground LNG storage systems in Singapore when exposed to accidental LNG leakage. [ABSTRACT FROM AUTHOR]

This study investigated the different geotechnical characteristics of soil stabilization with the addition of lime and rice husk ash (RHA) in varying amounts (3%, 5%, 7%, and 9% lime, and 4%, 8%, 12%, and 16% RHA). A series of compaction, unconfined compressive strength (UCS), California bearing ratio (CBR), pH, and X-ray diffraction (XRD) tests were performed in the laboratory to assess the impact of the considered admixtures on the stabilized soil parameters. This study also proposes the successful integration of an artificial neural network (ANN) and a Gaussian process regression (GPR) with the experimental UCS observations. The lime concentration, RHA concentration, and curing period were considered as the input parameters, and UCS was considered as the response. The proposed framework was extended to analyze the compressive behavior of treated soil on the minuscule level. Such coupled machine learning-based experimental investigation can provide deep insight into the soil behavior which otherwise would have remained unexplored due to the prohibitive nature of performing laboratory experiments on a large scale. The findings demonstrated the effectiveness of RHA in addition to lime in stabilizing the considered expansive soil. With the addition of lime and RHA mix, the UCS and CBR values of the treated soil increased significantly. [ABSTRACT FROM AUTHOR]

This paper addresses a soil bio-stabilization technique using bacterial enzyme-induced calcium carbonate precipitation (BEICP) as an alternative to previous conventional methods including microbial-induced carbonate precipitation and plant-derived enzyme-induced carbonate precipitation. The extracted urease enzyme of viable S. pasteurii was used as a biological source along with calcium chloride and urea to solidify sandy soil and silty sand soil. The bio-treated soil columns were subjected to freeze and thaw (F–T) cycling for a durability evaluation. Engineering properties of bio-cemented soil including unconfined compressive strength, calcium carbonate contents, moisture contents, porosity, permeability, and microstructure were examined before and after the F–T durations. It was found that although bio-stabilizer was able to increase a frost duration of soil, the F–T cycling significantly impacted on the compressive strength of bio-treated soil, due to a formation of microcracks. This investigation has revealed that the BEICP method provided a similar capacity in F–T resistance of soil as using the traditional Portland cement stabilizer, whereas the class F fly ash did not improve F–T durability of medium dense soil. [ABSTRACT FROM AUTHOR]

Sugarcane bagasse ash is a solid agroindustrial residue resulting from the burning of bagasse in boilers for energy cogeneration. The study objective of this review article is to systematically evaluate the use of sugar-cane bagasse ash as a pozzolanic component of a new sustainable waste application for soil stabilization in order to reduce the negative environmental impact of construction. The study method used was based on a specific analysis in the collection of the articles belonging to the time stratum from 2017 to 2021; where they are distributed as follows: 05 article from EBSCO, 48 from Scopus, 2 from SciELO and 25 from ScienceDi-rect. In conclusion, according to the critical study of the results found, we sustain that the use of the soil stabi-lization method successfully improves clay soil. [ABSTRACT FROM AUTHOR]

Cropland soils are key systems in global carbon budgets due to their high carbon-sequestration potential. It is widely accepted that clays are one of the soil components that have a significant effect on the stabilisation of soil organic carbon (SOC), owing to its surface interactions with organic molecules. However, the identification of the direct effects of clays on SOC stabilization is complicated, mainly due to the difficulty of accurately characterizing the mineralogy of clays, especially phyllosilicates. In this study, the relationships between soil phyllosilicates and functional SOC pools in woodlands and comparable olive groves, under two contrasting management systems (bare soils versus soil under cover crops) and parent materials (calcareous and siliceous), were explored. The total mineralogy of soil and clay fractions and the soil-clay assemblages were analysed through the decomposition of X-ray diffraction patterns, and were then related to four SOC pools. Total and unprotected SOC was higher in olive groves under cover crops, and this was true independent of the parent material, proving the importance of herbaceous covers in SOC sequestration in woody crops. Some significant correlations between clay minerals and SOC fractions were found. Interestingly, mixed-layer content was correlated with the biochemically protected SOC fraction (r = 0.810, p < 0.05), and this was so even when the partial correlation coefficient was calculated (r = 0.761, p < 0.05). According to the partial correlation networks (PCN), four separated clusters of variables were obtained, which joined into only one at fdr < 0.25. The PCNs supported the direct correlation between mixed-layer content, especially those rich in smectite, and the biochemically protected SOC fraction, suggesting that smectite layers may stabilize organic molecules. Since potassium enrichment is higher in the rooted layers of woodland and soils under cover crops, and this increase is related to the collapse of swelling layers, these soils were poorer in smectite phases than the bare soils. This also would explain why the biochemically protected SOC was more abundant in the latter. [ABSTRACT FROM AUTHOR]

Clayey soils have fine particles and contain clay minerals. Therefore, they are sensitive to water and cause stability problems. Nowadays, soil stabilization is an accepted method to resolve the problem of stability. In this study, hemp fiber was used as an additive material for stabilization of clayey soil. The use of fibers in the stabilization of clayey soils is becoming widespread, particularly with regard to applications involving the stabilization or reinforcement of shallow steep earth slopes and steep cover systems for landfills. In these applications, the use of natural fibers use is very important due to their environmentally friendly properties. Hemp legally planted in different countries is used in several industries, such as paper, textiles, clothing, biodegradable plastics, construction, body products, health food, and biofuel. In this study, hemp fiber was preferred because of its natural and environmentally friendly properties. To observe the effect of hemp fiber on the compressive strength of clayey soil material, the unconfined compression tests and shear box tests were carried out under laboratory conditions. The experimental results showed that hemp fiber is effective on the compressive strength of clayey soils. As a result, hemp fiber can be used successfully in clayey soil stabilization as an environmentally friendly material. [ABSTRACT FROM AUTHOR]

Considering that, in the context of the ecological restoration of a large number of exposed rock slopes, it is difficult for existing artificial soil to meet the requirements of mechanical properties and ecological construction at the same time, this paper investigates the stabilization benefits of polyvinyl acetate and attapulgite-treated clayey soil through a series of laboratory experiments. To study the effectiveness of polyvinyl acetate (PVA) and attapulgite as soil stabilizer, a triaxial strength test, an evaporation test and a vegetation growth test were carried out on improved soil with different amounts of PVA content (0, 1%, 2%, 3%, and 4%) and attapulgite replacement (0, 2%, 4%, 6%, and 8%). The results show that the single and composite materials of polyvinyl acetate and attapulgite can increase the peak deviator stress of the sample. The addition of polyvinyl acetate can improve the soil strength by increasing the cohesion of the sample; the addition of attapulgite improves the soil strength mainly by increasing the internal friction angle of the sample. The strength of the composite is greatly improved by increasing the cohesion and internal friction angle of the sample at the same time. The effect of adding materials increased significantly with increasing curing age. Moreover, polyvinyl acetate and attapulgite improve the soil water retention of the soil by improving the water-holding capacity, so that the soil can still ensure the good growth of vegetation under long-term drought conditions. The scanning electron microscopy (SEM) images indicated that the PVA and attapulgite of soil affect the strength characteristics of soil specimens by the reaction of PVA and water, which changes the structure of the soil and, by the interweaving of attapulgite soil particles, acts as the skeleton of the aggregate. Overall, PVA and attapulgite can effectively increase clayey soil stability by improving the cohesive force and internal friction angle of clayey soil. [ABSTRACT FROM AUTHOR]

This experimental study examines the efficacy of the inclusion of randomly distributed polypropylene fiber (PP) reinforcement on the engineering properties of expansive clays. The effect of PP fiber inclusions (0%-0.8%) on compaction, unconfined compressive strength (UCS), elastic modulus (E50), California bearing ratio (CBR) and swell-consolidation parameters of test soil were explored. Experimental results showed significant improvement in the strength parameters of treated soils with an optimal fiber content at about 0.4% by weight of soil. The swell-consolidation parameters were also observed to be significantly ameliorated in fiber-reinforced samples. Test results indicate that the use of PP fiber as a reinforced stabilizer for expansive clays not only benefits the sustainable utilization of fiber wastes in soil stabilization, but also reduces the environmental footprint globally. [ABSTRACT FROM AUTHOR]

Since clay is widely used in most construction projects, the issue of improving clay soils has considerable importance. This study aimed to optimize the variables affecting the properties of geopolymer and improve their mechanical properties using Isfahan blast furnace slag. Taguchi's statistical design method was used to model three process variables (blast furnace slag, water, and alkali sodium hydroxide agent) with four different values in the mixing design. Geopolymer was used to optimize the uniaxial compressive strength. Sixteen geopolymer compositions determined by mini-tab software were prepared and their uniaxial compressive strength was measured. The obtained results were modeled by analysis of variance, and then the interactions of the three variables on the uniaxial compressive strength of geopolymer were investigated using two and 3D diagrams. Then, the variables were optimized and the proposed values for the optimal sample were examined at temperatures of 25, 50, and 70°C and at times of 3, 7, 14, and 28 days of operation. A comparison of the results predicted by the models and the results of the experiments confirmed the validity of the models. Also, the scanning electron microscopy (SEM) images showed that the porosity will reduce from 7 to 28 days. It indicated that the use of the geopolymerization method has a significant role in stabilizing weak clay soils with low plasticity. The effect of fibers and geopolymer to reinforce was also investigated and for better evaluation, it was compared with soil stabilization with Portland cement. The results showed that in the most optimal geopolymer composition, the bearing resistance of clay has increased by more than 3400%. Meanwhile, fibers along with geopolymer with optimal percentage and length (0.1% by weight of geopolymer composition and length of 12 mm) were able to increase the uniaxial compressive strength of clay by nearly 4000%, which shows the excellent effect of using cellular fibers parameter whit the geopolymer in this research. [ABSTRACT FROM AUTHOR]

In construction, the foundation is an integral part of a structure and its function is to transfer the building loads safely into the ground and to keep the settlement within permissible limits. Here, soil is an essential component of the earth's surface that transfers building load through the foundation. Generally, different foundations are adopted depending on the different soil conditions and number of floor loads to be transferred to the deeper strata. Therefore, improving the bearing capacity of soil by experimental stabilization achieves better strength at required shallow depth. This paper develops an improved bearing capacity for shallow foundations on clays considering actual soil constitutive behavior. The geopolymer-stabilized soil specimens were synthesized and characterized with compressive strength testing and effective soil stabilizer for clay soils. [ABSTRACT FROM AUTHOR]

Volcanic ashes (VA) are one of the by-products of explosive volcanic eruptions. They can be used as a soil stabilizer due to their cementitious properties as an eco-friendly soil stabilization approach. In this study, the impact of VA as an additive material (up to 20%) was investigated on the behavior of a clayey soil under one-dimensional compression tests and uniaxial compression tests. To this aim, the VA percentage effect, curing conditions, i.e. the optimum moisture content (OMC) and saturated sample, and curing time, on the oedometer modulus, and the uniaxial compression strength (UCS) are investigated. Results show that the addition of VA increases the UCS continuously in saturated conditions. However, this improvement is considerable for 5% additional VA at the OMC state and it induces 325% improvement in UCS. The maximum improvement of UCS occurs at 20% addition of VA in saturated condition. It was also revealed that VA-soil mixtures are more sustainable at low stress levels and the oedometer modulus increases with the VA addition. A long-term curing time leads to an increase of the fabricated bonds due to the pozzolanic reaction. Additional VA has no significant effect on the consolidation parameters specifically for short-term curing time. [ABSTRACT FROM AUTHOR]

Oil pollution causes deterioration of the physical, chemical, mechanical, and geotechnical characteristics of affected soil leading to loss of soil productivity for engineering purposes. Different stabilization methods serve as a remedy for such soil to regain its loss engineering properties. This study was concerned with the utilization of lime to stabilize crude oil contaminated soil and to investigate its efficacy for soil stabilization. The study also focused on determining the geotechnical properties of crude oil contamination and matching the result with standard specifications established for engineering works. Hydrated lime, expansive clayey soil, contaminated soil, and potable water were the materials used for the experimental investigation. The contaminated soil was treated with 6.5% lime and 0–20% crude oil contaminated materials obtained from oil exploration sites in North-Eastern Nigeria and per standard test method for laboratory evaluation of consistency limits, compaction properties, California bearing ratio (CBR), and microstructural and mineralogical assessments. The experimental results obtained were further tested statistically through one-way ANOVA and F-statistics to establish the source of variation for the geotechnical properties, while multiple linear regression and correlation statistics helped draw the connection between the consistency limits, compaction, and CBR properties of the soil-lime-COCM blend. Results indicated a coefficient of determination of 99.86. The contaminated soil materials were found to show optimal performance at a 5% ratio and 6.5% of lime for civil construction purposes. [ABSTRACT FROM AUTHOR]

Weak subgrade is the main problem facing most highway projects. Therefore, this study focuses on trying to improve the properties and increase the strength of weak, clayey, swelling soil for use as a subgrade for pavement structural sections. This trial was developed using a mix of granular and chemical stabilization for the soil. Granular stabilization was applied firstly by mixing natural sand at different percentages of 20%, 35%, and 50% of the total weight of clayey, swelling soil samples to find the minimum percentage that could be added to improve it to sandy, clayey soil, which is acceptable as a subgrade according to the Egyptian highway specification code. Secondly, chemical stabilization was applied to enhanced sandy, clayey soil to increase its strength properties. This was performed by adding chemical additives (lime, cement kiln dust (CKD), fiberglass, Addicrete 11, and gypsum) at different ratios of 2%, 4%, and 6% of the total weight of the samples of enhanced sandy, clayey soil. An experimental program was conducted consisting of characteristics and consistency tests, the California bearing ratio (CBR) test, a proctor test, and a consolidated-drained (C-D) tri-axial shear test. The results showed that 50% sand was the minimum percentage that could be mixed with swelling, clayey soil for granular stabilization to be enhanced and become sandy, clayey soil, which is accepted as a subgrade layer according to the Egyptian highway specification code. In addition, using a mix of granular and chemical stabilization increased the compressive strength of this enhanced subgrade by adding 6% lime or cement kiln dust (CKD) of the total sample weight. They enhanced the strength of the soil and reduced its plasticity. Adding 6% fiberglass and polymers could slightly enhance the desired properties; however, it is not recommended to use them due to their slight effect and economic cost. In addition, it is not recommended to use gypsum at more than 4% due to its negative effect on CBR. [ABSTRACT FROM AUTHOR]

In recent years, there has been an increasing interest in investigating the use of non-traditional additives for stabilizing problematic soils. As the demand for eco-friendly alternatives to cement rises, magnesium chloride, a widely used deicer and dust suppressor, has emerged as a potential choice. This study aims to provide a comprehensive understanding of the microstructural changes that occur and affect the macro behavior of treated bentonite (B) and yellow marl (YM). To achieve this, MgCl 2 solution was added to the soils at 3, 6, 9, and 12 percent by dry weight of the soil, and samples were cured for 7, 14, and 28 days at 5° C , 25° C , and 35° C. The mechanical properties of the treated soils were then evaluated using the unconfined compression test, direct shear test, and pressure chamber test (SWCC), while microstructural analysis techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDAX), and Fourier transform infrared spectroscopy (FTIR) were employed to examine the mechanism of MgCl 2 stabilization. The results indicate that adding MgCl 2 and extending the curing period significantly increased both soils' unconfined compressive strength (UCS). However, the UCS value decreased for treated samples cured at temperatures higher than 25°C due to an incomplete cation exchange process and the reduction of apparent cohesion. A part of the gained strength from apparent cohesion and matric suction in the unsaturated samples was lost when the samples reached full saturation during the direct shear test. Changes in the particle size, pore size, and pore void distribution due to the MgCl 2 stabilization affected the SWCCs of the treated soils. Microstructural analyses revealed the formation of magnesium hydration products, such as magnesium silicate hydrate (M-S-H) and magnesium aluminate hydrate (M-A-H), which contributed to the strength increase by increasing grain size, filling the pores, binding fine particles within coarse grains, and forming a flocculated structure through recrystallization of MgCl 2 and the formation of cementitious gel. Additionally, for B, adding MgCl 2 led to soil flocculation through ion exchange, while for YM, the same process occurred due to the greater surface tension of the saline solution encircling the particles. • Microstructural analyses indicated the production of cementitious hydration products M-S-H and M-A-H. • Increasing curing temperature reduced the strength by decreasing the apparent cohesion. • The treatment of the B and YM with MgCl 2 decreased the LL and PI. • Stabilized soil structure changed to a flocculated, interlocked, and denser one. • UCS of both soils improved up to 110 % due to recrystallization and cementation of MgCl 2. [ABSTRACT FROM AUTHOR]

Soil stabilization is an in situ soil treatment in which soils are mixed with cementitious or other chemical stabilizing agents. Determining the unconfined compressive strength (UCS) of stabilized soil is a principal task in the design and construction of the ground improvement. Hence, this study aims to develop a reliable predictive model for the UCS of clay stabilization with common cementitious binders using the gene-expression programming (GEP) technique. Eleven parameters, including the soil characteristics, the binder types, the binder contents, the mixing method, and the curing period, were considered as the independent variables in the model. The research results show that the selected optimal GEP-based model performs well with an acceptable correlation coefficient (R = 0.951) and low errors (e.g., RMSE and MAE). Besides, parametric analyses indicate that the plastic index, the percentage of clay, and the total water content have a negative effect on the UCS of stabilized soil. In contrast, the percentage of silt and sand, the binder types, the binder contents, and the curing time show a positive effect on the strength of stabilized soil. In addition, the strength of stabilized clay could be significantly enhanced by combining cement with slag, lime, or fly ash with a reasonable ratio, or by reducing the natural water content in the soil. The research findings could help engineers choose suitable binder types and cost-effective methods to optimize the UCS of stabilized clay. [ABSTRACT FROM AUTHOR]

This study evaluates the use of rice husk ash (RHA)-eggshell lime (ESL) and RHA-commercial lime (CL) as alternative binders for clayey soil stabilization, as well as the performance of soil-binder mixtures under acidic attack. A central composite design was carried out to analyze the reactivity by batch tests with a sulfuric acid solution. Physical and mechanical behavior was evaluated by compaction test and unconfined compressive strength (UCS). Reactivity tests demonstrated better neutralization of contaminant acidity for mixtures with ESL. The highest compressive strength, reactivity and partial encapsulation of toxic elements are associated with application of 30% RHA and 6% ESL in the soil. A C–S–H gel is observed in poorly crystalline phases through the XRD pattern. The application of RHA-ESL in soils exposed to acidic attack has environmental feasibility. Analysis of RHA grinding processes combined with the mixture strength over time, and its application tests in impermeable barriers, in landfills, are recommended. [ABSTRACT FROM AUTHOR]

Efficient utilization of problematic soils such as soft clay by imparting additional strength using various stabilization techniques is done to improve soil properties. The application of nanomaterials in the area of soil stabilization has great potential to create a stiff skeleton, especially when blended with cementitious materials. Using the response surface method, this study focused on studying the effects of single and blended cementitious systems, comprising cement (0% to 20%), slag (0% to 20%), and nanosilica (0% to 2.4%), on the properties of soft clay in wet conditions [water-to-soil ratio (w/s) of 53% to 87%]. The mechanical [California bearing ratio (CBR), unconfined compressive strength up to 91 days] and durability (freezing-thawing durability factor) properties of stabilized clay were investigated, and the bulk trends were corroborated by thermogravimetry and microscopy analyses. Based on statistical analysis, incremental addition of cement, slag, and nanosilica led to the systematic increase in the properties of soft clay, albeit to different extents and with different mechanisms. At the low w/s (53%), superior mechanical and durability properties were obtained for soft clay stabilized with the ternary binder comprising cement, slag, and nanosilica. Numerical optimization showed that stabilizing this weak type of soft/expansive clay is possible, but the results (proportions, performance, cost) varied based on the target design criteria and application. [ABSTRACT FROM AUTHOR]

Plastic clays in subgrade may cause major engineering defects such as excessive heave or settlement during the wet season that contribute to the formation of uneven geometry at the pavement surface. Soil stabilization is often a requisite to ameliorate the engineering properties of soft soils or reactive clays. This study investigates the application of nano-silica and nano-alumina to improve the California bearing ratio (CBR) of a local clay. The clay was treated with cement (2%–8%), with nano-additive (0.1%–1.5%) and with cement and nano-additive (3% cement + 0.1%–1.5% nano-additive). The compacted sample was cured for 7 days and subjected to soaked and unsoaked CBR tests. The soaked CBR of the nontreated clay increased by 49% and 27% for 1% nano-silica and 1% nano-alumina treated clay, respectively. Although 3% cement addition improved the CBR of the soaked clay by 28%, the combination of 3% cement with 1% nano-silica and nano-alumina resulted in 196% and 164% increase in the soaked CBR of the nontreated clay, respectively. The combination of nano-additives and cement yielded the same soaked CBR as if 6%–7% cement would have been used. Clay treated with 1% nano-silica and 3% cement achieved the highest CBR value within the tested samples and the sample treated with 1% nano-alumina and 3% cement achieved the lowest free swell potential. The scanning electron microscopy (SEM) micrographs of the treated clay showed the formation of uniform fabric with fewer pore spaces and calcium silicate hydrate (CSH)/calcium aluminate hydrate (CAH) products within the fabric of nano-additive treated clay. [ABSTRACT FROM AUTHOR]

A zero carbon footprint stabilization approach has been adopted in this research to improve the swelling potential (SP) of clayey soils for a greener construction approach. Construction activities like earthworks during the cement stabilization of unstable soils utilized as reconstituted subgrade materials is responsible for the emission of unhealthy amount of carbon oxides into the atmosphere contributing to ozone layer depletion and eventual global warming. This has been substituted by using eco-friendly cementing materials, quicklime activated rice husk ash (QARHA), formulated in this research work. The SP of clayey soil treated with QARHA has been predicted using the learning abilities of genetic programming (GP), artificial neural network (ANN) and the evolutionary polynomial regression (EPR). This was aimed at reducing the over dependence on repeated laboratory visits and experiments prior to infrastructure (pavement) designs, construction and future monitoring of the performance of the facility. Multiple data were collected from multiple experiments based on the tested emergent material (QARHA) treatment proportions used in this work. The data were subjected to statistical analysis and predictive model exercises. At the end, the predicted models were validated on the basis of performance and accuracy. The performance indices showed that EPR and GP with R2 of 0.997 outclassed ANN with R2 of 0.994, but EPR outclassed the two, GP and ANN with a minimal error of 6.1%. The performances of GP, ANN and EPR were compared with a previously conducted model, which utilized the learning techniques of the adaptive neuro-fuzzy interface system (ANFIS) and it was observed that EPR and GP performed better than ANFIS but ANN performed at par with it. Generally, the predictive models can predict the SP of subgrade soil treated with QARHA, a non-carbon–based binder with accuracy above 90%, which is a very good outcome. [ABSTRACT FROM AUTHOR]

In this study, the mechanical and durability performance of clay soils reinforced with different proportions of Cherry Marble Powder (CMP) and non-woven geotextile configurations, both independently and in combination, is investigated in detail at both the macro and micro levels. The effectiveness of reinforcement in the stabilization of clay soils in cold climates has been evaluated by means of Gray Correlation Analysis (GCA). The results show that as the CMP ratio and the number of geotextiles increase, the peak strength of the soil increases, with higher CMP levels showing perfect plastic behavior and more geotextiles showing linear strain hardening, particularly in combination. Substantial strength reductions post-7th cycle ranged between 91.09 % and 103.38 % for 12 % CMP and 219.83 % and 270.42 % for three-layered geotextile groups. Cohesion increased by 59.76 % and 179.41 %, while the internal friction angles remained stable and decreased after F-T cycles, except with additives. Failure modes shifted with CMP content, F-T cycles and confining pressure. The transition was from strain hardening to strain softening, with increased shear fracture planes and brittleness. The energy absorption capacity (EAC) increased with the CMP ratio, with the geosynthetic reinforcement increasing the EAC by a factor of 1.5 before and after the F-T cycles. The combined use of CMP and geotextiles in soil stabilization improved the engineering properties in areas of frost, with the optimum gradation being three layers of geotextile and a CMP ratio of 12 %, which effectively mitigated the effects of the maximum F-T cycle. • CMP and geotextile increase soil strength pre and post F-T. • 7 cycles cause significant strength reduction: up to 103.38 % for 12 % CMP, 270.42 % for 3 layers. • Cohesion rises: 59.76 % in 1st stage, 286.96 % in 2nd, 83.99 % in 3rd, and 179.41 % in 4th. • EAC increased with CMP ratio, and geosynthetic boosted CMP's EAC by 1.5 times. • Failure modes shift from strain-hardening to strain-softening with CMP, F-T cycles, and pressure. [ABSTRACT FROM AUTHOR]

The study showcase the optimization of California bearing ratio (CBR) values of expansive soil treated with cement kiln dust (CKD) and metakaolin (MTK) blend based on Scheffe optimization method. The CBR values utilized in the design of road infrastructure is an important parameter because it provides the rating of soil material for use as subgrade, sub-base and/or base course of road pavement. Therefore, applying Scheffe optimization technique will eliminate the random selection of design mix ratios and other associated disadvantages during CBR tests. Based on the optimization exercise and it results, the maximum CBR (unsoaked and soaked) values of 69 and 50 % were achieved with a corresponding mix ratio of 1.0:0.30:0.35:0.50 for black cotton soil, water, cement kiln dust and metakaolin respectively. During the course of this study, the laboratory results were used to develop two CBR models. The scheffe models developed are Ŷ=34X1+46X2+40X3+69X4-8X1X2-4X1X3+34X1X4+8X2X3+34X2X4+30X3X4 and Ŷ=17X1+28X2+22X3+50X4-10X1X2-6X1X3+42X1X4+8X2X3+40X2X4+40X3X4 for CBR unsoaked and soaked, respectively. In addition, the mathematical models were statistically scrutinized, confirmed for the adequacy and validity based on the outcomes of student t-test and analysis of variance (ANOVA). Also, the scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) techniques were used to explore the morphological and composition variations of the natural soil in contrast with the typically optimized soil-CKD-MTK blend. However, the SEM of the unaltered soil sample showed a smooth like surface, whereas the soil mixture optimally treated does not show same but rather demonstrated a rough like surfaced morphology. Thus, the observed variations might be due to the alterations of the soil fabrics possibly enhanced by the development of cementitious compounds (calcium silicate hydrate and calcium aluminate hydrate) as a result of pozzolanic reaction. [ABSTRACT FROM AUTHOR]

Carbide lime is a by-product obtained during the manufacturing of acetylene from the reaction of calcium carbide and water. A major portion of carbide lime is dumped in waste deposition areas, creating an environmental problem. Carbide lime and fly ash have possible applications in slope stabilization, subgrade improvement of roads, and soil treatments under shallow foundations. A series of Atterberg limits tests, compaction tests, unconfined compressive strength tests, ultrasonic pulse velocity tests, and wetting–drying tests were performed on carbide lime and fly ash treated clay soils to evaluate the effects of additive content, curing time, strength development, and the effects of wetting and drying. A total of 8% of carbide lime constituted the fixation point, and peak strength was achieved at 12% carbide lime content. A total amount of 25% additive was found as a threshold changing the Atterberg limits. Test results indicated that the strength of the treated soil improved by the existence of carbide lime and fly ash; best performance was observed in 28-day specimens with 10% carbide lime and 20% fly ash content reaching to 8 times larger strength than untreated soil. The failure patterns of the specimens reflected the curing time and wetting–drying effects. Although, the application of wetting–drying cycles deteriorated the treated soil, the presence of carbide lime partially prevented the strength loss. New relationships between normalized strength and curing time depending on carbide lime content were proposed. Furthermore, a linear relationship between the unconfined compressive strength and the ultrasonic pulse velocity of the treated soils was established. [ABSTRACT FROM AUTHOR]

Cement stabilization is a soil improvement technique widely adopted for soft soils. The extent of improvement to the physical properties varies largely with soil type and often requires laborious laboratory tests to ascertain such extent of improvement when soil samples from a source are obtained. To offer a quick estimate of the improved unconfined compressive strength of the composite, it is crucial to develop relationships of the strength with essential parameters of the soil. Furthermore, existing studies mainly focused on cement-stabilized clays with minimal granular content. The influence of commonly encountered sand impurities in actual field condition is much less discussed. In view of these limitations, the current study explores the use of activity number (A), liquid limit (wL) and modified apparent void ratio (ec*) as a proxy to unify the strength development of cement-stabilized soft soils used for land reclamation in the modified Abrams's strength predictive model. Incorporation of A and wL is achieved by introducing a new parameter α. Friction due to geometric proximity between sand particles in the composite is represented by ec*. Results show that the proposed model is able to successfully consider the effect of soil properties in the strength development of soils stabilized with Ordinary Portland cement (CEM I) and Portland blast-furnace cement (CEM III/C) and validated with published literature. The proposed models enable quick check of the design when only mix proportions and index properties are available. They also incorporate the influence of sand content, which is merely considered in existing models. [ABSTRACT FROM AUTHOR]

The swelling potential analytics and the ion exchange reaction of highly expansive soils in a soil stabilization process have been reviewed. The importance of these factors in deciding suitable construction materials and chemical additives utilized as alternative or supplementary binders in clayey soil stabilization has been discussed also. The outcome of this study has shown that Al3+, Si4+, and Ca2+ are the most suitable exchangeable cations with OH- as the suitable exchangeable anion leading to the formation of C-A-S-H, which is the compound responsible for strengthening. The swelling potential analytics also proposed the expression wsT = 0.00216 × (Σi=1 i=n Ip1 2.44) (Σi=Dn i=D1 Di) as the total swelling potential with respect to the depth of a foundation material constructed with clayey soil. This study revealed that during the wet season, hydraulically bound foundation materials experience undesirable volume changes with the highest swelling potential expected at the surface within the active (unstable) zone of the foundation. Generally, the treatment of highly expansive soil with very high swelling potential should be concentrated at the surface and reduced along the depth of the foundation matrix. With this proposed guide, the utilization of alternative or supplementary cementing materials as construction materials in the stabilization of clayey soil to improve swelling can be conducted with a more sustainable approach. [ABSTRACT FROM AUTHOR]

Problematic soil stabilization processes involve the application of binders to improve the engineering properties of the soil. This is done to change the undesirable properties of these soils to meet basic design standards. However, very little attention has been given to the reactive phase of soil stabilization. This phase is the most important in every stabilization protocol because it embodies the reactions that lead to the bonding of the dispersed particles of clayey soil. Hence, this reactive phase is reviewed. When clayey soils which make up the greatest fraction of expansive soil come in contact with moisture, they experience volume changes due to adsorbed moisture that forms films of double diffused layer on the particles. When this happens, the clayey particles disperse and float, increasing the pore spaces or voids that exist in the soil mass. Stabilizations of these soils are conducted to close the gaps between the dispersed clayey soil particles. This is achieved by mixing additives that will release calcium, aluminum, silicon, etc., in the presence of adsorbed moisture, and a hydration reaction occurs. This is followed by the displacement reaction based on the metallic order in the electrochemical series. This causes a calcination reaction, a process whereby calcium displaces the hydrogen ions of the dipole adsorbed moisture and displaces the sodium ion responsible for the swelling potential of clayey soils. These whole processes lead to a pozzolanic reaction, which finally forms calcium alumina-silica hydrate. This formation is responsible for soil stabilization. [ABSTRACT FROM AUTHOR]