Expansive soil, characterized by significant swelling-shrinkage behavior, is prone to cracking under wet-dry cycles, severely compromising engineering stability. This study combines experimental and molecular dynamics (MD) simulation approaches to systematically investigate the improvement effects and micromechanisms of polyvinyl alcohol (PVA) on expansive soil. First, direct shear tests were conducted to analyze the effects of PVA content (0 %-4 %) and moisture content (30 %-50 %) on the shear strength, cohesive force, and internal friction angle of modified soil. Results show that PVA significantly enhances soil cohesive force, with optimal improvement achieved at 3 % PVA content. Second, wet-dry cycle experiments revealed that PVA effectively suppresses crack propagation by improving tensile strength and water retention. Finally, molecular dynamics simulations uncovered the distribution of PVA between montmorillonite (MMT) layers and its influence on interfacial friction behavior. The simulations demonstrated that PVA forms hydrogen bonding networks, enhancing interlayer interactions and frictional resistance. The improved mechanical performance of PVAmodified soil is attributed to both nanoscale bonding effects and macroscale structural reinforcement. This study provides theoretical insights and technical support for expansive soil stabilization.

The main problem in expansive soil treatment with steel slag (SS) is the relatively slow hydration reaction that occurs during the initial period. To circumvent this, SS-treated expansive soil activated by metakaolin (MK) under an alkaline environment was investigated in this study. Based on a series of tests on the engineering properties of the treated soil, it can be reported that SS could enhance the strength and compressibility of expansive soil, with strength increasing by approximately 108 % for SS contents exceeding 10 % compared to 3 % lime-treated soil, and the compression index reducing by 20 %. Further addition of MK plays a dual role, enhancing strength for higher SS content while excessive MK leads to strength reduction due to insufficient pozzolanic reactions and hydration product transformation. Expansive and shrinkage behaviors are notably improved, with a 5 % increase in SS content reducing the free swelling ratio by 0.66 %-5.9 %, and the combination of 15 % SS and 6 % MK achieving a nearly 300 % reduction in the linear shrinkage ratio. Microstructural analysis confirms the formation of hydration gels, densification of the soil structure, and reduced macropores, validating the enhanced mechanical and shrinkage resistance properties of the SS-MK-treated expansive soil. Additionally, to develop predictive models for mechanical and the content of hardening agents (SS and MK), the experimental data are processed utilizing a backpropagation neural network (BPNN). The results of BPNN modeling predict the mechanical properties perfectly, and the correlation coefficient (R) approaches up to 0.98.

Currently, the application of enhancement techniques with natural additives for soil stabilization is crucial due to growing urbanization and environmental concerns. Contemporary construction methods increasingly need eco-friendly and cost-effective materials, such as natural fibers. Reinforcing the soil sublayers with fibers improves layer quality and increases its load transfer capacity over a larger surface, thereby reducing the required thickness of upper layers. This study utilized raspberry stalks and xanthan biopolymer as natural additives for the first time to improve the mechanical qualities of bentonite expansive soil. Different tests, including compression and indirect tensile strengths, swelling potential, freeze-thaw (F-T) cycles, California bearing ratio (CBR), and scanning electron microscopy (SEM), were performed on samples comprising 0.2, 0.4, and 0.6 % of raspberry fibers and 0.5, 1, and 2 % of xanthan gum, with curing durations of 1, 7, 14, and 28 days. The test results revealed that the combination of 1 % xanthan and 0.4 % fibers, subjected to 28 days of curing, showed the best performance in increasing the mechanical properties of bentonite. The hydrogel structure and the locks and links formed in the soil by the additives led to increases of 353 % and 103 % in compressive and tensile strengths, respectively. The results also indicated that the free-swelling potential of the unstabilized bentonite soil diminished from 280 % to 74 % when stabilized with optimum percentages of xanthan and fiber. Furthermore, the investigation showed that even after exposure to 10 F-T cycles, the durability of xanthan-fiber-stabilized bentonite soil was significantly higher compared to the unstabilized soil. Moreover, the CBR value of the stabilized soil improved by 143 % compared to the unstabilized soil, indicating a significant increase in soil layer quality. The SEM results verified that the additive combination significantly impacted the strength of the samples. The data indicate that the incorporation of xanthan gum as a bio cohesive agent and raspberry fiber as tensile strands enhances soil strength, hence augmenting the viability of these additives in practical applications, including shallow foundations, adobe brick, and subgrade.

The rapid depletion of natural aggregate resources has led to the exploration of recycled aggregates as sustainable alternatives. The steel industry annually generates 28 million tons of magnesia-based waste refractories (WMRs), making their incorporation into construction materials a potential strategy for resource conservation. However, WMR recycling poses a challenge because of its susceptibility to volume expansion during hydration. This study evaluated the feasibility of an environmentally friendly additive, lignosulfonate (LS), for stabilizing crushed waste magnesia refractory bricks (CWMR) to explore the potential application of WMR as construction aggregates. The swelling properties, including the free swell index (FSI) and the swell pressure (Ps), and mechanical properties including unconfined/uniaxial compressive strength (qU), shear wave velocity (VS), and thermal conductivity (lambda) of LS stabilized CWMR (CWMLS) were evaluated over different curing periods at varying LS contents (LSc). Hydration transformed CWMR from sandlike to highly plastic silt-like, resulting in a significant FSI of 250 % and Ps of 5.2 MPa. LS effectively stabilized CWMR, as indicated by decreased FSI and Ps, and enhanced qU and VS. Microscopic observation and mineralogy analyzes confirmed that LS stabilizes CWMR by adsorbing onto its surface. Stabilization of thermal conductivity at higher LSc over curing periods further supports these interactions. Macroscopic behavioral analyzes give stabilized effect of 94.3 % at LSc = 5 % with minimal improvement at higher LSc. These findings highlight LS as a promising stabilizer for mitigating hydration-induced expansion and improving the mechanical properties of CWMR, supporting its application as a recycled aggregate in construction.

A common physical technique assessed for improving expansive clays is by the addition of natural fibres to the soil. A good understanding of the impact of stabilisation using fibres on the clay soil's constituents, microfabric, and pore structure is, however, required. Mixtures of clay and fibre, regardless of type or extent, can never change the natural composition of the clay. Even the smallest part must still consist of spaces with clay with the original physical properties and mineralogy. This suggests that, although the mixture may show beneficial physical changes over the initial clay soil, its spatial attributes in terms of mineralogical characteristics, remain unchanged. This paper discusses some of the fundamentals that are not always adequately considered or addressed in expansive clay research, aiming to improve the focus of current and future research investigations. These include the process, mechanics, and implications of chemical and physical soil treatment as well as the concept of moisture equilibration.

This experimental study is to find a solution to reduce the amount of waste and at the same time improve the geotechnical properties of fine soils. Compaction, odometer, direct shear tests, and unconfined compression tests were carried out on a clay with a very high degree of plasticity mixed with 0%, 10%, 20%, 30%, and 40% of recycled concrete aggregates (RCA). The addition of concrete aggregates to the clayey soil shows an increase in the maximum dry density and a reduction in the optimum water content. The odometer tests results showed that the increase in the recycled material content leads to a decrease in the compression index, swelling index and creep index. On the other hand, the pre-consolidation stress, the odometric modulus, the consolidation coefficient and the permeability coefficient increase with increasing RCA content. According to the direct shear test, the higher RCA content provided an improvement in shear strength which is accompanied by an increase in the dilatant character. For different curing times and for a content of 10% recycled concrete aggregate, the unconfined compressive strength increased compared to the untreated soil.

Expansive soils, with their pronounced swell-shrink behavior, pose significant challenges to structural stability and durability. This study introduces an innovative stabilization approach by integrating natural (jute) and synthetic (nylon) fibers with cement to enhance the mechanical properties and volumetric stability of expansive soils. The unique synergy between natural and synthetic fibers is a key feature, leveraging the surface roughness and bonding capacity of jute with the durability and tensile strength of nylon to create a robust and stable soilfiber-cement matrix. Experimental evaluations, including unconfined compressive strength (UCS), indirect tensile strength (ITS), California bearing ratio (CBR), 1D swell tests, and linear shrinkage tests, revealed significant improvements: UCS, ITS, and CBR values increased by up to 1380 %, 1565 %, and 1450 %, respectively. The inclusion of fibers, in combination with cement, significantly enhanced UCS, ITS, and CBR values by up to 109 %, 200 %, and 11 %, respectively, compared to cement-only stabilization. The optimal fiber content of 0.5 % for both jute and nylon maximized these enhancements, effectively mitigating moisture-induced volume changes by reducing free swell strain and swell pressure by over 90 %. Linear shrinkage was also substantially minimized, improving soil durability and structural integrity. Microstructural and chemical analyses using scanning electron microscopy (SEM) and Fourier-transform infrared (FTIR) spectroscopy confirmed the formation of a dense matrix with enhanced particle interlocking and the development of calcium silicate hydrate (C-S-H) gel, providing chemical stabilization. The findings underscore the potential for this methodology to revolutionize soil stabilization practices, offering durable and environmentally responsible options for geotechnical and civil engineering applications.

This study investigates the potential application of a blend, termed GGRM, consisting of red mud (RM) and ground-granulated blast furnace slag (GGBS), for stabilizing subgrade expansive soil. RM, an industrial waste from aluminium refineries, poses environmental concerns due to its high alkalinity and presence of heavy metals. Despite its increased utilization in construction sector, research on its role in soil stabilization is limited. With this in mind, RM has been used as an activator for GGBS, to create synergy between these industrial wastes with an objective to utilize this blend for stabilization of black cotton soil (BCS). Therefore, laboratory investigations were conducted to assess the strength of BCS stabilized with GGRM comprising varying proportions of GGBS and RM (0:100, 70:30, 50:50, 30:70, and 100:0 by weight). Further, the optimal GGRM quantities were evaluated by mixing it in different proportions (5-30% by weight). This study also examined the effect of curing on strength properties and leaching behaviour and investigated the associated mechanisms through microstructural studies (XRD, XRF, SEM, and FTIR analysis). The leachate potential was assessed using ICP-OES analysis. Results indicated a maximum sevenfold improvement in unconfined compressive strength of BCS, from 131 to 920 kPa, after 28 days of curing in 70:30 combinations with 25% GGRM content. Furthermore, leaching of heavy metals from stabilized soils are within the permissible limits of hazardous waste management regulations. In conclusion, RM-activated GGBS blends emerged as a potentially sustainable binder, enhancing the strength of expansive soil for subgrade applications.

This article evaluates the long-term wet-dry durability of lime, fly ash, and lime-fly ash slurry injection stabilization of expansive soil in the desiccated state. To achieve this objective, the expansive soil was compacted in large cylindrical test moulds and desiccated after making a central hole for slurry injection. Subsequently, the lime slurry/ fly ash slurry/ lime-fly ash slurry, prepared with the predetermined water-binder ratio, was injected into the desiccated expansive soil and cured for 28 days. The test results of lime and lime-fly ash slurry injected soils showed that there is improvement during the first wetting. However, at the end of four wet-dry cycles, the volumetric deformations of lime- and lime-fly ash slurry-treated soils increased to 10.6% and 13.6%, respectively, which are much lower than the volumetric deformation of untreated soil (30.7%). Additional analyses were also conducted to trace the growth of desiccation cracks of both untreated and treated soils. At the end of the third drying cycle, the total percentage of the cracks (surface cracks + annular gap) in lime slurry- and lime-fly ash slurry-treated soils reduced to 1.18% and 5.37% from the untreated soil value of 31.9%. The findings of the present study underline the positive impact of using lime, and lime in conjunction with fly ash for controlling the volume change behaviour of expansive soils. Furthermore, combination of lime and fly ash significantly reduces the consumption of lime, leading to sustainability in geotechnical practices.

Improper anti-drainage treatment of weakly expansive soil subgrades can lead to significant post-construction deformation and uneven settlement, which severely affect the operational safety and service life of engineering projects. To comprehensively analyze the evolution of soil volume and strength under different hydraulic coupling paths during wetting-drying (W-D) cycles, a loaded W-D cycle testing device was developed. Soil volume was measured during the W-D cycles, and the shear strength and soil-water characteristic curves were analyzed after different cycles. The results indicate that during the W-D cycles, changes in soil volume and strength exhibited distinct stages with similar evolution characteristics. Under the investigated loading conditions, the soil demonstrated significant collapsibility during the wetting process, which gradually diminished as the number of cycles increased. Eventually, the W-D cycles caused the soil to reach an equilibrium state, where its swelling and shrinkage behavior became nearly elastic. At equilibrium state, there is a corresponding void ratio for any moisture content, which is the elastic void ratio (e0el). The e0el is irrespective of the number of cycles and initial dry density. Conversely, higher load and larger amplitude in W-D cycles tend to decrease the e0el. Furthermore, by correlating the unsaturated soil matric suction, secant modulus, and stress path, the volume evolution mechanism of the soil was analyzed based on the soil effective stress theory and pore evolution. The results of this study can serve as a crucial reference point for revealing the deformation mechanism of weakly expansive soil subgrades and selecting appropriate road settlement control methods.