The treatment of soil with biopolymers has demonstrated various benefits, including strength enhancement, reduction in the permeability coefficient, and promotion of vegetation. Consequently, numerous experiments have been conducted to evaluate the strength of biopolymer-treated soils. This study aims to evaluate the interparticle bonding strength attributed to the biopolymer network formed between soil particles, focusing on the strength characteristics at the particle scale. Agar gum, a thermo-gelling biopolymer, was selected to assess the strength of biopolymer solutions. Experiments were conducted at concentrations of 2 %, 4 %, and 6 % with varying drying times to account for the differences in water content. The bonding, tensile, and shear strengths of the agar gum polymer solutions were evaluated under different loading conditions. To compare the strengths and meaningful trends observed in the agar gum polymer solution under different conditions. The results demonstrated that for all strength conditions involving the agar gum solution, the strength increased with higher concentrations and lower water content. During the particle size test, the bonding strength was improved up to 160 kPa, and the tensile strength of the agar gum polymer itself was observed to be up to 351 kPa. Furthermore, the UCS test results of the silica sand mixed with agar gum showed an improvement up to 1419 kPa. Among the evaluated strengths, the tensile strength was the highest, whereas the shear strength was the lowest. A comparison between the adhesive strength tests, which evaluated the strength characteristics at the soil particle scale, and the UCS of silica sand mixed with an agar gum solution revealed a similar trend. The shear strength increased consistently with drying time across all concentration conditions, which was consistent with the trends observed in the UCS. These findings suggest that the strength characteristics of soils treated with agar gum solutions can be effectively predicted and utilized for ground improvement applications.

Ground granulated blast furnace slag (GGBS), calcium carbide slag (CS), and phosphogypsum (PG) were combined in a mass ratio of 60:30:10 (abbreviated as GCP) to solidify dredged sludge (DS) with high water content. The long-term strength characteristics of solidified DS under varying curing agent dosage and initial water contents, as well as its durability under complex environmental conditions, were investigated via a series of mechanical and microstructural tests. The superior performance of GCP-solidified DS (SDS-G) in terms of strength and durability was demonstrated in comparison to solidified DS using ordinary Portland cement (SDS-O). The results indicated that the unconfined compressive strength (UCS) of SDS-G was approximately 3.0-4.5 times greater than that of SDS-O at the same dosage and curing ages, exhibiting a consistent increase in strength even beyond 28 days of curing. Additionally, the strength and deformation modulus (E50) of SDS-G increased initially and then decreased during wet-dry cycles, with reductions in mass, volume, and strength significantly were smaller than those observed in SDS-O. Furthermore, the reductions in UCS and E50 induced by freeze-thaw cycles were considerably smaller for SDS-G than for SDS-O, with strength losses of 50.7 % and 88.3 %, respectively, after 13 freeze-thaw cycles. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses revealed that the enhancements observed in SDS-G were attributed to the formation of ettringite (AFt), which effectively fills larger pores between agglomerated soil particles, thereby creating a denser and more stable microstructure in conjunction with hydrated calcium aluminosilicate (C- (A)-S-H) gels.

Acid contamination has a notable influence on the geotechnical properties of soil and this influence is strongly dependent on contamination concentration (pH) and contamination duration. To fully investigate the effect of acid contamination on the microscopic and strength properties of natural clay, a series of micro- and macrolaboratory tests were performed in this study, and the mechanism of this effect was comprehensively revealed. Microscopic analysis indicates that acid contamination could lead to some mineral transformations in clay, such as illite-smectite transforming into chlorite and illite transforming into kaolinite. Besides, more large pores and a looser structure can be observed in the clay due to the erosional effects of acid contamination, which could effectively weaken the strength properties of natural clay. The experimental results also indicated that, when subjected to acid contamination, the lower contamination pH could lead to a notable decrease in clay's shear strength, while the clay's shear strength increased initially and then decreased as contamination duration increased. In addition, gray correlation analysis results demonstrated that calcite has a significant effect on cohesion, while also indicating a strong correlation between illite and the internal friction angle.

Binders can enhance soil properties and improve their suitability as subgrade fillers; however, the cementing effect and strength properties of solidified soil are highly susceptible to external environmental factors. This study evaluated the strength and durability of solidified sludge soil (PSCS) with varying binder (PSC) contents through unconfined compressive strength (UCS) tests combined with drying-wetting (D-W) and freezing-thawing (F-T) cycles, and identified the optimal binder content for performance enhancement. Additionally, mercury intrusion porosimetry (MIP) tests were conducted to analyze pore structure changes and explore the synergistic effects between hydration reactions and moisture variations induced by D-W/F-T cycles. Results indicate that binder content > 15 % significantly enhances PSCS strength and durability, with 15 % content (PSCS15) demonstrating the best economic advantage. During D-W/F-T cycles, the synergy between hydration reactions and moisture variations affects the pore structure, resulting in strength changes. For example, during D-W cycles, moisture movement causes the collapse of pores > 30 mu m, while hydration products fill the pores, decreasing the porosity of 5-30 mu m. Subsequently, moisture variations weaken the cementation effect, leading to a increase in the porosity of 5-30 mu m. This process causes the strength to fluctuate, showing a first decrease, followed by an increase, and then another decrease, with an overall reduction of 21.6 %. During the drying stage of D-W cycles, moisture evaporation inhibits hydration reactions in soil. In contrast, during F-T cycles, moisture remains in different physical states (e.g., solid ice crystals and liquid water). These moisture variations causing the collapse of pores >30 mu m, while hydration products fill the larger pores, increasing the porosity of 1-10 mu m. The strength first decreases and then increases, with an overall increase of 38.7 %. Furthermore, this study demonstrates that until the hydration process is completed, D-W cycles have a more significant negative impact on PSCS compared to F-T cycles.

Conventional curing agents are associated with environmental impacts when treating Zn(2+)contaminated soils. To overcome this limitation. In this study, we study a new type of MgO-CSB curing agent. Namely, corn stover biochar is modified with activated MgO. Modification of corn stover biochar using activated MgO, and carbonation curing was adopted to solidify/stabilize the Zn(2+)contaminated soil. The curing efficacy of Zn(2+)contaminated soil under modified mass ratio, Zn2+ concentration, carbonation time, and curing agent incorporation was investigated. The findings indicate that the optimal adsorption efficiency was attained following the co-pyrolytic modification of activated MgO with corn stover biochar at 700 degrees C. The optimal modified mass ratios for curing were found to be 1:1, 1:2, and 2:1 at Zn2+ concentrations of 0.1 %, 0.5 %, and 1 %, respectively. At a lower Zn2+ concentration, peak carbonization intensity is achieved at 0.5 hours, while at a 1 % Zn2+ concentration, peak intensity is reached at 1 hour. The deformation modulus of the cured soil increases as the curing agent dosage increases and the soil aggregates become denser. SEM results show that: The carbonization and curing reaction products are mainly nesquehonite and Mg (OH)(2). The internal structural damage of the cured soil was aggravated by the increase in Zn(2+)concentration, and the generation of nesquehonite and Mg (OH)(2) was inhibited; The carbonation time was extended to 1 h and the soil structure stability was enhanced.

Purpose Straw fiber (SF) is a natural and environmentally friendly material, which has great potential in improving the hydro-mechanical behavior of cemented dredge sediment. However, the treatment mechanisms and optimum application dosage of SF in cemented sediment at high water content are unclear. This study investigates the effect of SF on the shear strength and permeability of cemented sediment at high water content (3 times the liquid limit). Methods Various SF contents (0%, 0.3%, 0.5%, 1%, 3%, 5%, 8% and 12% by mass) and curing ages (3, 7, 14, 28, 60, 90, 180 days) were considered to improve cemented dredged sediment. The effectiveness of the improvement was evaluated through unconfined compression and permeability tests. Results The test results show that there is an optimum SF content of 0.5%, below which the unconfined compression strength (q(u)) of SF-reinforced cemented sediment (SFCS) increased with SF content. Beyond this point, q(u) decreased with SF content. The brittleness index (I-b), which indicates the ductility behavior, increased with SF content across the entire SF range (0-12%). When SF addition was relatively low (< 0.5%), pore filling and bridge effects increased the interface force between SF and sediment particles, resulting in positive effects on the improvement of SFCS strength. However, when SF content exceeded 0.5%, the higher organic matter from SF could suppress pozzolanic reaction, leading to weaker cemented bonding between sediment particles and hence lower sediment strength. Conclusion This study suggests that 0.5% SF should be applied in cemented dredged sediment at high water content to optimize its strength.

This study investigated the impact of adding different proportions of ground granulated blast furnace slag (GGBS) on the engineering properties of expansive soils. GGBS proportions ranging from 0 to 40% by weight of soil were tested. A comprehensive series of experiments was conducted to determine the consistency limits, modified compaction characteristics, unconfined compression test of soil, and California bearing ratio (CBR) values under varied curing conditions of the stabilized soil mixtures. The results indicated that a GGBS content of 30% provided the optimum improvement, enhancing the strength and stability of the material. Additionally, a laboratory dynamic cone penetration test was performed inside a CBR mould to further examine the improved performance of the expansive soil samples with incorporated GGBS. The findings demonstrate that GGBS can significantly enhance the engineering behavior of expansive soils when added at 30% by weight. The research underscores the significant positive impact of GGBS on the engineering properties of expansive soils, offering an effective and environmentally friendly means of disposing of steel industry waste.

This experimental research has been conducted to improve the mechanical properties of the problematic expansive soil using copper slag. The copper slag has been utilized to improve the Talab soil in Nainwa for the first time. The swelling properties show that the collected soil has a high degree of expansive nature and low specific gravity. Therefore, the copper slag has been added to the soil from 5% to 30% at a 5% variation by its oven-dry weight. The experimental results reveal that the free swell index of soil has decreased by 69.88% with the addition of 30% copper slag. It has also been observed that the liquid and plastic limits have been decreased. The plastic limit of soil decreases, because copper slag takes place in voids. Due to this phenomenon, the maximum dry density of soil has been increased by 14.75% with the addition of 25% copper slag. The California bearing ratio (CBR) value of soil has been increased to 1.13% (soaked condition) and 3.8% (unsoaked condition) by adding 25% copper slag. This research introduces an empirical relationship between unsoaked and soaked CBR with a determination coefficient (R2) of 0.8254. Moreover, it has been observed that the unconfined compressive strength of soil has increased by 51.68% with the addition of 25% copper slag. Furthermore, the value of R2 for the experimental results obtained in this research is higher than the published experimental results, presenting the experimental study's accuracy and reliability. In addition, the analysis of variance (ANOVA) test accepts the research hypothesis for the present investigation.

This study investigates the effect of nanosilica and plantain leaf ash on the sustainable stabilization of expansive soil. This study conducted various strength tests, including Unconfined Compressive Strength (UCS), direct shear, and California Bearing Ratio (CBR) tests, to analyze the enhancement of mechanical properties by adding nano silica and plantain leaf ash. Scanning Electron Microscopy (SEM) analysis was conducted to investigate the interaction mechanism between the soil and the combination of nano silica and plantain leaf ash. Three different combinations of plantain leaf ash were utilized, ranging from 5% to 15%, alongside nano silica ranging from 0.4% to 1.2%. The reinforced soil's compressive strength, shear strength, and bearing capacity were assessed through UCS, direct shear, and CBR tests. The results demonstrated significant improvements in compressive strength, up to 4.6 times, and enhancements in cohesion and frictional angle, up to 3.3 and 1.6 times, respectively, at 28 days. Moreover, the addition of nano silica and plantain leaf ash led to increased bearing capacity and reduced soil swelling potential, contributing to the overall stability and strength improvement in expansive soil. The SEM test results demonstrate that maximum bonding and compaction occur when 1.2% nano silica and 15% plantain leaf ash are added to the soil.

Artificial ground freezing (AGF) technology is sometimes adopted to reinforce the surrounding soil to ensure the safety of subway tunnels during construction in the eastern coastal areas of China. The mechanical characteristics of frozen soil are subjected to change due to the incorporation of chlorine salt, and the soil strength decreases significantly with an increase of salt content. The mechanical properties of frozen silty clay have been rarely investigated due to the coupling effect of temperature, strain rate, and salt content. In this study, before the application of AGF, a series of unconfined compressive strength (UCS) tests and the consolidated-undrained static triaxial compression tests were conducted on frozen silty clay to investigate the influence of salt content, temperature, and strain rate on the mechanical properties of frozen soil. From the stress -strain curves of the UCS test, strain -hardening and strain -softening behavior were identified as a result of the influence of different temperatures and salt contents. Regression analysis was performed to discriminate the effect of each individual factor and their coupling effect. The results reveal that soil UCS logarithmically increased with a decrease in relative temperature and strain rate. Both UCS and static triaxial strength linearly decreased with an increase in salt content. The influence of salt content on the strength of frozen soil was discussed and compared with previous researches. Furthermore, an elastic -plastic constitutive model was proposed to characterize the stress -strain behavior in which the effects of strain rate and salt content were included. At last, with consideration of salt content, a modified constitutive model was proposed to describe the strength and deformation behavior of frozen silty clay.