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This paper presents a comprehensive investigation on the microstructural evolutions of expansive clay during a drying–wetting cycle, including pore size distribution (PSD) via mercury intrusion porosimetry and water distribution via nuclear magnetic resonance (NMR). The soil water characteristic curves at different soil densities and soil shrinkage curve are also obtained, and a threshold suction can be identified to distinguish the adsorptive and capillary regimes of pore water. Combined with the water distribution obtained by the NMR technique, the evolutions of the adsorptive water and capillary water during drying–wetting cycle were addressed. The measured PSD curves of the expansive soils at different suctions showed two distinct peaks, corresponding to micropores and macropores, respectively. Both variations of macropores and micropores are irreversible during the wetting–drying cycle, which partly explain the adsorptive water content decreasing when the suction is small.

Expansive soil, a problematic clay soil susceptible to significant volume changes with moisture variation, is typically mitigated using cohesive non-swelling soil (CNS) covering technology. This study evaluates the comprehensive performance and feasibility of using chemically stabilized expansive soil (CSS) treated with hydroxy-aluminum solution as a replacement for natural CNS as a covering layer for expansive soil (ES). Through a series of physical-mechanical tests, chemical analyses, and laboratory model tests, the inhibition effect of different covering layers (CSS, CNS, and gravel) on expansive soil was investigated, along with the relationship between electrical resistivity and swelling deformation. The results indicate that: (1) After modification with hydroxy-aluminum solution, the engineering properties of expansive soil were substantially improved, with shear strength enhanced and swelling percentage significantly reduced. Overall, CSS exhibited performance comparable to that of CNS. (2) The CSS layer provided the most effective inhibition of expansive soil, reducing swelling deformation by approximately 67%--a clear improvement over both gravel and CNS layers, thereby confirming the viability of CSS as an alternative covering material. (3) A strong correlation was observed between the resistivity ratio and the swelling rate of the expansive soil layer. Specifically, this relationship followed a linear function under the gravel and CNS layers, whereas it exhibited a power function under the CSS layer. These findings offer valuable insights for the engineering application of CSS covering technology and for the use of electrical resistivity as a practical evaluation method.

Aims This study investigates the complex interactions between urban trees and expansive clay soils, focusing on two prevalent species ( Corymbia maculata and Lophostemon confertus ) in Melbourne’s urban landscape. Limited field data and understanding of species-specific water use necessitate this research. We aim to quantify the spatiotemporal variability in soil-plant-water interactions within the urban contexts, a crucial factor for informed green infrastructure planning and sustainable ecosystem management in metropolitan areas. Methods Comprehensive field measurements were conducted over 12 months, including soil movement, soil water dynamics, tree transpiration, and leaf water potential. Sap flow sensors monitored tree water requirements. Laboratory soil testing determined soil properties and developed soil suction and water content profiles. The intercorrelation between soil water dynamics and tree water use was investigated. Results Peak water use for both trees occurred during summer, contributing 32–40% of their total consumption. C. maculata transpired 48.1 kL, exceeding L. confertus by 106%. The trees’ desiccation influence extended horizontally to 0.4–0.5 times the tree height and vertically to 2.3–3.3 m depth. Soil water content explained 31–36% of soil movement variability, with a strong correlation (R² > 0.9) between soil suction and water content within the active root zone. Conclusions This study enhances our mechanistic understanding of urban tree-soil interactions, providing valuable insights for sustainable city planning. It emphasizes species-specific considerations in tree selection and placement, especially in areas with expansive soils. The robust field data contributes to refining predictive models of soil-plant-atmosphere interactions in urban landscapes, supporting informed decision-making in urban greening initiatives.

Expansive soils are a prevalent issue in road construction, particularly in regions like Ethiopia. They pose significant challenges due to drastic shrink-swell behavior. Traditional stabilizers such as cement and lime are effective but costly and raise environmental concerns. This necessitates exploring more sustainable, locally-sourced alternatives. This research explores using Barley Husk Ash (BHA), an agricultural byproduct, as a pozzolanic additive to stabilize expansive soil from Jimma, Ethiopia. The untreated soil had an initial PI of 39% and a CBR of 0.8%. The study had two phases. First, optimal lime content was determined by treating the soil with varying lime percentages (0–20%) in 5% increments. Second, this lime content was combined with BHA in similar 5% increments (0–20%). Adding 10% lime reduced the PI to 22%, increased the CBR to 9.72%, and raised the Unconfined Compressive Strength (UCS) to 137 kPa. This met the Ethiopian Roads Authority (ERA) S4 subgrade standard (CBR>5%). Adding 10% BHA to the 10% lime-stabilized soil further improved performance. The PI dropped to 18% and the CBR increased to 18.42%, qualifying the soil for the higher S5 subgrade classification (CBR 15%-30%). Microstructural analysis using SEM confirmed these findings. The BHA-lime blend created a denser, more cohesive soil matrix with enhanced inter-particle cementitious bonding. This explains the improved strength and reduced swell potential. The mean porosity also decreased from 17.33% to 6.74%. This research validates a 10% lime plus 10% BHA blend as a highly effective, sustainable, and locally available solution for modern road construction.

Expansive clayey soils often pose challenges for construction projects due to their low bearing capacity, swelling, and shrinkage properties. While previous research has explored additives to enhance these soils’ properties, the potential of sand remains underexplored. This study investigates the impact of varying sand percentages on expansive clayey soils’ consistency, compaction, and permeability. This study examines how adding different percentages of sand influences the physical properties of expansive clayey soils. Laboratory tests involved systematic testing of texture, compaction, and permeability. Findings reveal a notable improvement in the physical properties of the soil with the addition of sand. Results from the laboratory tests provided data for empirical equations that facilitate the prediction of soil properties based on the sand content. The enhancement in soil properties underscores the potential of sand as an additive for expansive clayey soils. The empirical equations presented here provide practical benefits to geotechnical engineers and practitioners engaged in construction projects involving these soils, offering them valuable insights into the benefits of sand additives to improve physical characteristics. The insights gained from this research hold promising prospects for improving construction practices and addressing the challenges associated with these soils.

The efficiency of typical chemical and mechanical soil stabilization techniques in mitigating the swelling problem of an expansive soil is investigated through a comprehensive experimental study. Chemical stabilization was generated by traditional agents consisting of lime and cement, and by a commercially branded polymer (CBR PLUS). Mechanical stabilization was applied by means of fiber-reinforcement and swell–shrink cycles. Chemically-treated and fiber-reinforced soil samples were tested for swelling potential in a conventional oedometer apparatus; while swell–shrink cycles were applied using a modified temperature-controlled oedometer. Swell–shrink cycles were applied under room temperature for wetting cycles while the drying process was conducted under a constant temperature of 40 ± 5 °C, and swelling and shrinkage potential were recorded during successive cycles to a point in which swell–shrink equilibrium was attained. Typical strength tests were also conducted for each stabilization scenario which led to maximum reduction in swelling potential. In addition to the experimental program, the swell–time relationship for various stabilization scenarios was simulated using a two-parameter rectangular hyperbola function (2P-RH). Results indicated that all of the proposed stabilization scenarios can guarantee a significant reduction in swelling potential. In the case of lime and cement, reduction in swelling potential was observed to be a function of agent percentage and curing time; whereas for polymer-treated samples the effect of curing was found to be insignificant. Regarding fiber-reinforced samples, reduction in swelling potential was a function of fiber percentage, aspect ratio and fiber tensile strength. Overall, traditional agents proved to be more effective compared to non-traditional techniques. The proposed non-traditional methods, however, displayed promising results posing as great alternatives to lime and cement.

Understanding expansive soil behavior under variable environmental conditions is crucial for environment and engineering contexts. This study investigates the deformation mechanism and mechanical behaviors of expansive soil with varied moisture contents under dry–wet cycles. Through theoretical analysis and laboratory tests, we first analyzed the elastic–plastic behavior of expansive soil under dry–wet cycles and then explored the elastic–plastic deformation, fracture characteristics, and mechanical properties therein. Results indicate that the soil aggregates evolve through the four stages of stable, compact, loose, and damaged structures under the dry–wet cycles. The swelling–shrinkage deformation consists of elastic and plastic components, and the magnitude of elastic expansion is always smaller than that of plastic expansion. Meanwhile, the cracks develop with the increased water content and the increased number of cycles. The aperture of the induced cracks increases as the water content increases. Accordingly, the shear strength sequentially decreases with the increasing number of cycles and the increasing moisture content. The decrease in shear strength with the increasing cycles is primarily due to structural damage accumulation followed by the reduction of cohesion, while the decrease with increasing water content is primarily due to the reduction in matric suction and the increased lubrication between soil particles and aggregates. In addition, the cohesion decreases with the increasing moisture content and the increasing number of cycles. However, the friction angle decreases only with a clear increase in the number of cycles, showing less sensitivity to dry–wet cycles in general.

This study aims to assess the suitability of micro-silica (MS) as an industrial waste to modify the hydro-mechanical behavior of expansive soil in comparison with the use of lime as a traditional stabilizer. Due to limitations associated with soil treatment with calcium-based materials, the effect of lime–micro-silica (LMS) on stabilization of expansive clay was also studied with the aim of reducing the amount of lime consumption. The clay was stabilized with different percentages of lime alone (3% and 5%), MS alone (10% and 20%) and mixtures of LMS (3–10%, 5–10%, 3–20% and 5–20%). Experimental study performed on treated and untreated specimens included the reactivity tests measuring the pozzolanicity of the additives, compaction characteristics and Atterberg limits of mixtures, one-dimensional swell, compressibility, shrinkage, unconfined compressive strength of compacted specimens of different mixtures, as well as X-ray diffraction, scanning electron microscopy and wet chemistry analysis to study the mineralogy, microstructure and chemical composition of specimens. The results showed that the addition of MS alone did not have a significant effect on the stabilization of expansive soil, whereas stabilization with LMS achieved promising results with 10% MS + 3% lime mixture, hence achieving the goals of recycling MS as well as minimizing the amount of lime used. This combination was effective in improving the hydro-mechanical behavior of the clay due to formation of cementitious compounds resulting from pozzolanic reactions between Ca2+ of lime and SiO2 of micro-silica.

Expansive soil is prone to cracks under a drying–wetting cycle environment, which brings many disasters to road engineering. The main purpose of this study is use coal gangue powder to improve expansive soil, in order to reduce its cracks and further explore its micro-pore mechanism. The drying–wetting cycles test is carried out on the soil sample, and the crack parameters of the soil sample are obtained by Matlab and Image J software. The roughness and micro-pore characteristics of the soil samples are revealed by means of the Laser confocal 3D microscope and Mercury intrusion meter. The results show that coal gangue powder reduces the crack area ratio of expansive soil by 48.9%, and the crack initiation time is delayed by at least 60 min. Coal gangue powder can increase the internal roughness of expansive soil. The greater the roughness of the soil, the less cracks in the soil. After six drying–wetting cycles, the porosity and average pore diameter of the improved and expanded soil are reduced by 37% and 30%, respectively, as compared to the plain expansive soil. By analyzing the cumulative pore volume and cumulative pore density parameters of soil samples, it is found that the macro-cracks are caused by the continuous connection and fusion of micro-voids in soil. Coal gangue powder can significantly reduce the proportion of micro-voids, cumulative pore volume, and cumulative pore density in expansive soil, so as to reduce the macro-cracks.

Expansive soils exhibit pronounced swelling-shrinkage behavior, low shear strength, and high moisture sensitivity, posing significant challenges to the stability of geotechnical structures such as embankments and tailings dam slopes. In this study, a sustainable stabilization strategy integrating enzyme-induced carbonate precipitation (EICP) with iron ore tailings is investigated to improve the hydro-mechanical performance of expansive soils. A comprehensive experimental program was conducted to evaluate changes in unconfined compressive strength (UCS), swelling pressure (P s ), hydraulic conductivity (K s ), cohesion (c), and internal friction angle (φ). Microstructural characterization using scanning electron microscopy and X-ray diffraction was performed to examine calcium carbonate precipitation and its cementation effects within the soil matrix. The results demonstrate that the combined EICP-iron ore tailings treatment significantly enhances soil performance, with UCS, c, and φ increasing by approximately 113%, 48%, and 98%, respectively, while P s and K s decrease by approximately 98% and 69%. Furthermore, seepage and slope stability analysis using GeoStudio (SEEP/W and SLOPE/W) indicate that the stabilized soil achieves a markedly higher factor of safety (FoS = 1.896) compared to untreated soils. The findings confirm that the synergistic integration of EICP and iron ore tailings provides an effective, environmentally sustainable, and engineering-feasible solution for stabilizing expansive soils and improving slope performance in tailings dam applications.