Conventional in-situ light non-aqueous phase liquid (LNAPL) remediation techniques often face challenges of high costs and limited efficiency, leaving residual hydrocarbons trapped in soil pores. This study investigates the efficiency of an alcohol-in-biopolymer emulsion for enhancing diesel-contaminated soil remediation. The emulsion, formulated with xanthan gum biopolymer, sodium dodecyl sulfate surfactant, and the oil-soluble alcohol 1-pentanol, was evaluated through rheological tests, interfacial tension measurements, and onedimensional sand-column experiments under direct injection and post-waterflooding scenarios. The emulsion exhibited non-Newtonian shear-thinning behavior with high viscosity, ensuring stable propagation and efficient delivery of 1-pentanol to mobilize trapped diesel ganglia. It achieved 100 % diesel recovery within 1.2 PV during direct injection, outperforming shear-thinning polymer-only and polymer-surfactant solutions, which achieved recovery factors of 83.4-92.9 %. Post-waterflooding experiments also demonstrated 100 % diesel recovery within 1.3 PV, regardless of initial diesel saturation. Key mechanisms include reduced interfacial tension, diesel swelling and mobilization induced by 1-pentanol, and uniform displacement facilitated by the emulsion's viscosity. Additionally, the emulsion required lower injection pressures compared to more viscous alternatives, enhancing its injectability into the soil and reducing energy demands. These findings highlight the emulsion's potential to overcome conventional remediation limitations, offering a highly effective and sustainable solution for diesel-contaminated soils and groundwater.

Compacted clays are extensively used as cover barriers to control rainfall infiltration and upward migration of greenhouse gases at municipal solid waste landfills and volatile organic compounds at industrially contaminated sites. Xanthan gum (XG) amendment offers a green and low-carbon solution to improve gas breakthrough pressure and reduce gas permeability of compacted clays, sustainably improve earthen structures. This study aimed to systematically investigate the effects of XG amendment on gas breakthrough pressure, gas permeability, and hydraulic conductivity of compacted clay liners. The gas breakthrough pressure increased from 0.6 kPa to 2.2 kPa (improve similar to 4 times) and the gas permeability decreased from 2.2 x 10(-14) m(2) to 4.8 x 10(-16) m(2) (reduce similar to 200 times) when the XG dosage increased from 0 % to 2 % and apparent degree of saturation was 100 %. Hydraulic conductivity of XG-amended soil at 1 % XG dosage was 2.6 x 10(-10) m/s, which was 3 % of the value measured in unamended soil. Mechanisms of enhanced gas barrier and hydraulic performance were interpreted by the combined effects of (i) soil pore filling substantiated by the analyses of scanning electron microscopy and pore size distribution; (ii) high viscosity of XG hydrogels, validated by the measurement of rheological properties; and (iii) increased diffuse double layer thickness of the amended soils evidenced by the zeta potential analysis.

This study investigated the effects of natural polysaccharides-guar gum (GG) and xanthan gum (XG)-on the properties and structure of illitic clay. Clay samples were prepared using five different GG and XG solutions, with polysaccharide concentrations of 0.5%, 1.0%, 1.5%, 2.0%, and 2.5%. The physical, mechanical, and hygroscopic properties of the samples were evaluated, along with water erosion resistance and structural characteristics, using SEM analysis. The addition of GG or XG significantly increased compressive strength and water erosion resistance, reduced shrinkage, and slightly improved the bulk density compared to the control clay sample. The results showed that compressive strength increased by 28-63% and 46-84% with the incorporation of GG and XG solutions, respectively. These findings suggest that environmentally friendly clay-based building materials can be effectively produced even using small amounts of natural polysaccharides.

Targeting the engineering properties of poor strength and susceptibility to damage in roadbeds and slopes within clay regions, xanthan gum is employed as a soil enhancer, concurrently addressing the issue of the low utilization rate of plant coir fiber. The unconfined compressive strength test (UCS) is used to analyze the influence of different maintenance methods, maintenance duration, xanthan gum dosage, and coconut fiber dosage on the mechanical properties of the enhanced soil. Furthermore, based on scanning electron microscope (SEM) tests, the underlying mechanisms governing the mechanical properties of fiber-reinforced xanthan gum-improved soil are uncovered. The results indicated that the compressive strength of amended soil is significantly enhanced by the incorporation of xanthan gum and coir fiber. After 28 days of conditioning, the compressive strength of the amended soil under dry conditions (conditioned in air) was significantly higher (3 MPa) than that under moist conditions (conditioned in plastic wrap) (0.57 MPa). Xanthan gum influenced both the compressive strength of the specimens and the degree of strength enhancement, whereas coir fibers not only augmented the strength of the specimens but also converted them from brittle to ductile, thereby imparting residual strength post-destruction. Microscopic analysis indicates that the incorporation of xanthan gum and coconut shell fiber significantly diminishes the number of pores and cracks within the soil matrix, while enhancing the internal inter-particle cementation. This synergistic effect contributes to soil improvement, providing theoretical and technical guidance for roadbed enhancement and slope repair.

The application of novel materials that enhance soil engineering properties while maintaining vegetation growth represents an innovative strategy for ecological protection engineering of expansive soil slopes. Laboratory tests, including wetting and drying cycle tests, direct shear tests, unconfined swelling ratio tests, and vegetation growth tests, were conducted to analyze the effects of xanthan gum on both engineering and vegetation-related properties of expansive soil. The feasibility of xanthan gum for soil improvement was systematically evaluated. The interaction mechanism between xanthan gum and expansive soil was elucidated through scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses. Results demonstrated that xanthan gum effectively inhibited crack development and strength loss. With increasing xanthan gum content, the crack area ratio decreased logarithmically by up to 58.62%, while cohesion increased by 82.96%. The unconfined swelling ratio exhibited a linear reduction, with a maximum decrease of 43.58%. Notably, xanthan gum accelerated seed germination rate but did not significantly affect long-term vegetation growth. Mechanistically, xanthan gum improved soil properties via two pathways: (1) forming bridging structures between soil particles to enhance cohesion and tensile strength; (2) filling soil voids and generating a polymer film to inhibit water-clay mineral interactions, thereby reducing hydration membrane thickness. These findings offer both theoretical insights and practical guidelines for applying xanthan gum in ecological protection engineering of expansive soil slopes.

A sustainable solution to stabilise the expansive soil over cement stabilisation is needed to avoid the negative environmental impact. Therefore, in this study, two biopolymers (such as xanthan gum and guar gum) were used to stabilise the expansive soil, and the study focused on the impact of curing (field and laboratory curing) conditions on the performance of biopolymer stabilisation. The compressive strength results showed that the treated sample achieved a higher strength up to 4.18 times with XG than the untreated soil sample strength with 28 days of curing (in FC) with 1.5% of the weight of the soil sample with both biopolymers. Conversely, the sample cured in LC was observed to have a very low strength increment, and the gained strength was lost with the curing period from 7 days to 28 days. The possible reason behind this phenomenon is that in moist conditions, the biopolymer presence in the hydrogel form reduces the soil particle interaction, and it is also due to the breakage of the soil-biopolymer matrix. The swelling pressure of the soil was significantly reduced compared to untreated soil. The microstructural and element composition analysis confirmed that the biopolymer treatment is not involved in any cementitious reaction.

Conventional pump-and-treat technologies have demonstrated limited effectiveness in remediating soils contaminated with light non-aqueous phase liquids (LNAPLs), such as petroleum hydrocarbons. Nonconventional in-situ flushing with shear-thinning fluids, such as polymers, offers a promising alternative. However, even with polymer flushing, residual LNAPL ganglia may remain trapped in porous media, requiring further improvement of the flushing fluid to enhance remediation efficiency. In this study, we present a novel alcohol-in-biopolymer emulsion developed to enhance the recovery of residual diesel oil from porous media. Batch experiments were conducted to evaluate the partitioning behavior of fifteen different alcohols between the aqueous and diesel phases. The results revealed that 1-pentanol preferentially partitions into the diesel phase rather than the aqueous phase, leading to an increase in diesel oil volume via a swelling mechanism. Furthermore, 1-pentanol forms a stable and homogeneous emulsion when combined with an aqueous solution of the biopolymer xanthan gum, and the surfactant sodium dodecyl sulfate. The emulsion demonstrated high stability for over 30 days, ensuring its suitability for prolonged remediation processes. Rheological experiments confirmed the emulsion's shear-thinning behavior, which ensures stable and uniform displacement within porous media. A two-dimensional cell packed with silica sand was used to evaluate the efficiency of the emulsion in removing residual diesel oil. The results demonstrated that the emulsion propagates uniformly throughout the porous media, effectively achieving complete removal of residual diesel within 1.15 pore volumes of injection. Porescale visualizations revealed the swelling and subsequent mobilization of entrapped diesel ganglia induced by the emulsion, further confirming its efficacy. These findings highlight the potential of this novel alcohol-inbiopolymer emulsion to significantly improve diesel oil recovery from contaminated soils.

Biopolymer-based soil treatment (BPST) enhances soil strength through biofilm matrix formation within soil voids. This study investigates the effects of biopolymer concentration, porosity, and soil packing conditions on biopolymer distribution and connectivity after dehydration. Laboratory experiments assessed the degree of biopolymer filling (DoBF), final condensed biopolymer concentration, and biopolymer film connectivity under simple cubic and rhombohedral packing conditions. The results show that higher initial biopolymer concentrations increase final biopolymer volume, though not proportionally due to threshold effects. Rhombohedral packing results in higher final condensed biopolymer concentrations than simple cubic packing, despite having lower DoBF values, while biopolymer connectivity peaks at an optimal porosity (n approximate to 0.35). Further analysis revealed a strong correlation between biopolymer matrix formation and soil mechanical properties, including uniaxial compressive strength (UCS), cohesion, and friction angle. UCS was found to decrease with increasing porosity, and a predictive model was developed using experimental data. The rhombohedral and simple cubic packing conditions respectively define the upper and lower bounds of the shear parameters. A back-calculation approach confirmed that DoBF provides the most accurate estimation of friction angle and UCS, reinforcing its importance as a key parameter in soil stabilization. These findings emphasize the need for optimized biopolymer concentration and soil structure adjustments to enhance reinforcement efficiency. The study offers valuable guidance for geotechnical applications, enabling the development of optimized biopolymer injection strategies that enhance mechanical performance and promote efficient material utilization.

The objective of this study was to enhance the mechanical properties of gravelly soil and to consider the binding and filling effects of xanthan gum and calcium lignosulfonate. To this end, gravelly soil samples were prepared with various dosages of xanthan gum and calcium lignosulfonate, and their curing effects were investigated. The mechanical properties and strength parameters of the cured gravelly soil were investigated using unconfined compressive strength (UCS) tests and conventional triaxial compression tests. Furthermore, scanning electron microscopy (SEM) was employed to examine the microstructure and curing mechanisms of the gravelly soil treated with these additives. The findings demonstrate that as the dosage increases, both xanthan gum and calcium lignosulfonate markedly enhance the compressive strength and shear strength of the gravelly soil. The curing effect of xanthan gum was found to be more pronounced with higher dosages, while the optimal curing effect for calcium lignosulfonate was achieved at a dosage of 4%. The gravelly soil treated with xanthan gum exhibited superior performance compared to that treated with calcium lignosulfonate when the same dosage was used. Moreover, at elevated confining pressures, the binding effect of xanthan gum and calcium lignosulfonate on the gravelly soil was less pronounced than the strength effect imparted by the confining pressure. This suggests that the impact of dosage on the shear strength of the gravelly soil is diminished at higher confining pressures. The stabilization of crushed stone soil by xanthan gum is a complex process that involves two main mechanisms: bonding and cementation, and filling and film-forming. The curing mechanism of calcium lignosulfonate-cured gravelly soil can be summarized as follows: ion exchange, adsorption and encapsulation, and pore filling and binding effects. The findings of this research offer significant insights that are pertinent to the construction of high earth-rock dams and related engineering applications.

In biopolymer-soil stabilization, biopolymers function in the soil either as viscous fluids or rigid gels. However, the influence of these hydrogel states on soil liquefaction resistance and their underlying mechanisms remain insufficiently understood. This study examines the seismic response of sand treated with biopolymers under small-to-medium strain cyclic loading, with a focus on the efficacy of Cr3+-crosslinked xanthan gum (CrXG) in mitigating liquefaction. Liquefaction resistance and dynamic properties of CrXG-treated soil were compared against thermogelation and non-gelling viscous biopolymer treatments using cyclic direct simple shear and resonant column tests. CrXG treatment at 1 % content improved liquefaction resistance (CRR10) from 0.088 to 0.687 by preventing shear strain accumulation and pore pressure buildup, with enhancing dynamic shear stiffness and delaying stiffness degradation and damping ratio changes to higher strain levels. In contrast, soils treated with non-gelling viscous XG exhibited limited reinforcement under large strain cyclic loading, showing earlier liquefaction and lower CRR10 compared than untreated sand, alongside reduced dynamic shear modulus and rapid stiffness degradation. Comparisons across varying earthquake moment magnitudes revealed that CrXGtreated soil achieved liquefaction resistance comparable to other soil stabilization methods and demonstrated greater improvement efficiency than thermogelation biopolymers requiring thermal treatment. These findings highlight the potential of CrXG as a sustainable and practical solution for improving liquefiable soil stability under seismic loading.