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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 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.

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.

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.

Swelling potential (SP) has long been used as a terminology to describe a soil's expansibility. It is commonly defined in terms of pressure or deformation under certain constraints. However, fundamentally, SP originates from the soil‐water interactions in the interlayer space of expansive minerals and should not depend on displacement or force constraints. Here, the writers propose a SP based on the concepts of soil sorptive potential, unitary definition of matric potential, and water retention hysteresis. Water retention hysteresis in low matric potential is the result of interlayer hydration against the interlayer energy barrier. This energy barrier prevents water from entering the interlayer space. SSP synthesizes all the known sources of water adsorption, which provides the energy for soil swelling and can be determined under the unified definition of matric potential. The SP is defined as the energy hysteresis of interlayer hydration during wetting and drying. It is a function of relative humidity and can be calculated solely from the soil water isotherm (SWI). The SWI data of a wide variety of fine‐grained soils are used to determine and assess the proposed SP. For validation, the SP index (SPI), defined as the maximum energy consumed to overcome the energy barrier during wetting, is used. The SPI compares well with several expansive soil classification systems, confirming the validity of the SP. This study provides a scientific basis for linking soil water potential and energy used for swelling and understanding the volumetric behavior of expansive soil under varying humidity environments.

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.

This study presents a sustainable method to enhance expansive soil performance by integrating enzyme induced carbonate precipitation (EICP) with basalt fiber (BF) reinforcement. Laboratory experiments were conducted using an optimized EICP 0.75 mol/L concentration and 1.5% BF (12 mm length). The results demonstrated that the combined treatment substantially reduced the swelling pressure and permeability (k s ) by up to 95% and 72%, respectively. This combined approach surpassed the effectiveness of the individual treatments, as EICP alone resulted in an 80% decrease in swelling pressure and a 63% reduction in k s . Additionally, synergetic treatment enhanced the engineering properties of the expansive soil. Specifically, the unconfined compressive strength increased 136%, cohesion 58%, internal friction angle 89%, unsoaked CBR 738%, and soaked CBR 911%, respectively. These enhancements were considerably more substantial than those obtained through EICP treatment alone, which yielded improvements of only 66, 43, 48, 441, and 435%, respectively. Additionally, microscopic analysis, scanning electron microscopy, demonstrated that while EICP deposits calcium carbonate within soil pores, the incorporation of BF provided additional structural reinforcement by bridging particles and enhancing interfacial bonding. These results underscore the combined effect of bio-cementation and fiber reinforcement, presenting an eco-friendly and durable technique for enhancing expansive soils in civil engineering projects.

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.

The construction of buildings on expansive soils poses considerable risk of damage or collapse due to soil shrinkage or swelling made likely by the remarkable degree compressibility and weak shear resistance of such soils. In this research, rice husk ash (RHA) was added to expansive soil samples in different quantities of 0%, 4%, 8%, 12%, and 16% by weight of soil to determine their effects on the plasticity index, compaction parameters, consolidation performance, and California bearing ratio (CBR)of clay soil. The results show that the use of RHA increases the effective stress and decreases the void ratio and coefficient of consolidation. Adding 16% RHA resulted in the greatest reduction in the hydraulic conductivity, void ratio, and coefficient of consolidation. The void ratio decreased from 0.96 to 0.93, consolidation coefficient decreased from 2.52 to 2.33 cm2/s, and hydraulic conductivity decreased from 1.12 to 0.80 cm/s. The addition of RHA improved the soil properties and coefficient of consolidation due to the high density and cohesiveness of RHA. The results of this study can be used to provide a suitable basis for the treatment of expansive soil to provide improved conditions for infrastructure construction.