This investigation examines the development of titanium slag-flue gas desulfurized gypsum-Portland cement ternary composites (the ternary composites) for the solidification and stabilization of Pb-contaminated soils. The efficacy of the ternary composites is systematically evaluated using a combination of experimental methodologies, including mechanical properties such as unconfined compressive strength, stress-strain behavior and elastic modulus, leaching toxicity, XRD, TG-DTG, FTIR, XPS, and SEM-EDS analyses. The results indicate that the mechanical properties of Portland cement solidified Pb-contaminated soils are inferior to those of Portland cement solidified Pb-free soil, both in the early and later stages. However, the mechanical properties of Pbcontaminated soils solidified by the ternary composites are superior to those of the ternary composites solidified Pb-free soils in the early stage but somewhat inferior in the later stage. The ternary composites significantly decrease the leached Pb concentrations of solidified Pb-contaminated soils, which somewhat increase with the Pb content and with the pH value decrease of the leaching agent. Moreover, with much lower carbon emissions index and strength normalized cost, the ternary composites have comparable stabilization effects on Pbcontaminated soils to Portland cement, suggesting that the ternary composites can serve as a viable alternative for the effective treatment of Pb-contaminated soils. Characterization via TG-DTG and XRD reveals that the primary hydration products of the ternary composite solidified Pb-contaminated soils include gypsum, ettringite, and calcite. Furthermore, FTIR, XPS and SEM-EDS analyses demonstrate that Pb ions are effectively adsorbed onto these hydration products and soil particles.

This paper aims to investigate the tunnelling stability of underwater slurry pressure balance (SPB) shields and the formation and evolution mechanisms of ground collapse following face instability. A laboratory SPB shield machine was employed to simulate the entire tunnelling process. Multi-faceted monitoring revealed the responses of soil pressure, pore water pressure, and surface subsidence during both stable and unstable phases. The morphological evolution characteristics of surface collapse pits were analyzed using three-dimensional scanning technology. The experimental results indicate that: (1) The key to stable tunnelling is balancing the pressure in the slurry chamber with the tunnelling speed, which ensures the formation of a filter cake in front of the cutterhead. (2) The torque of the cutterhead, soil pressure, and surface subsidence respond significantly and synchronously when the tunnel face becomes unstable, while the soil and water pressures are relatively less noticeable. (3) Excavation disturbance results in a gentler angle of repose and a wider range of collapse in the longitudinal direction of the collapsed pit. (4) A formula for predicting the duration of collapse is proposed, which effectively integrates the evolution patterns of the collapse pit and has been well-validated through comparison with the experimental results. This study provides a reference for the safe construction of tunnel engineering in saturated sand.

The large amount of slag generated during the construction of earth pressure balance shield (EPBS) not only incurs significant disposal costs, but also exacerbates environmental pollution. To improve the utilization of the shield slag, silty clay with additive is proposed as a slag conditioner instead of bentonite. Firstly, various macroscopic properties of the bentonite and silty clay slurries are tested. Subsequently, the relationships between the macroscopic properties of the silty clay slurries containing additives and the modification mechanism are evaluated at microscopic, mesoscopic, and macroscopic scales by using infrared spectroscopy (IR), scanning electron microscope (SEM), and Zeta potential tests, respectively. Based on these tests, reasons for variations in modification effects of different slurries are identified. The results show that addition of 3 % sodium carbonate to the silty clay can effectively improve the rheological properties of the slurry. The modification mechanism of sodium carbonate involves the formation of hydrogen bonds between water molecules and inner surface hydroxyl groups within the lattice layer of kaolinite. This process significantly enhances the rheological properties of the silty clay slurry. Furthermore, sodium carbonate alters the contact relationships between the silty clay particles, which increases viscosity and reduces permeability of the slurry. Finally, sodium carbonate increases thickness of the electrical double layer of the silty clay particles. This allows the particles to bind more water molecules, therefore improving slurry-making capacity of the silty clay. This paper presents an innovative multiscale analysis of the modification process of silty clay. The substitution of recycled silty clay for bentonite as a slag conditioner not only substantially reduces the cost of purchasing materials, but also considerably decreases the expenses associated with transportation and disposal of the soil discharged by EPBS.

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.

Tobacco is one of China's key economic crops, known for its wide distribution, high yield, and renewability. Tobacco stalk fibers (TSFs) share a similar chemical composition to wood fibers, making them a potential reinforcement for plant fiber composites. However, the waste tobacco stalk fibers raw material utilization rate is very low, and wasteful phenomenon is very serious. In this study, we prepared biodegradable TSF/PBAT composites using waste tobacco stalk fibers and polybutylene adipate-co-terephthalate (PBAT) through melt blending and injection molding techniques. The effects of different modifiers on the performance of the composites were systematically investigated, with a particular focus on their influence on the degradation behavior. The results showed that the waste tobacco straw fiber can be used as a reinforcing fiber for PBAT. The addition of modifiers significantly improved the mechanical properties of the composites and effectively slowed down the degradation rate in the soil environment. Among the modifiers, the combined use of maleic anhydride (MA) and hydroxylated multi-walled carbon nanotubes (OM) produced the best results, with the tensile strength and flexural strength of the composite reaching 17.3 MPa and 28.0 MPa, respectively-representing increases of 74.7% and 57.3% compared to the untreated composite. After 16 weeks of soil degradation, the mass loss rate of the MA/OM-modified composite decreased from 10.50 to 6.34%. This study provides a comprehensive exploration of the entire lifecycle of TSF-reinforced PBAT composites and offers important theoretical support for the resource utilization and value-added application of waste tobacco stalks in the field of green composite materials.

In cold regions' engineering applications, cement stabilized soils are susceptible to strength degradation under freeze-thaw (F-T) cycles, posing significant challenges to infrastructure durability. While metakaolin (MK) modification has shown potential in enhancing static mechanical properties, its dynamic response under simultaneous F-T cycling and impact loading remains poorly understood. This study investigates the dynamic mechanical behavior of cement-MK stabilized soil through split Hopkinson pressure bar (SHPB) tests under varying F-T cycles. The effects of strain rate and F-T cycles on the dynamic failure process and mechanical properties of cement-MK stabilized soil were investigated. Pore characteristics were analyzed using a nuclear magnetic resonance (NMR) system, providing an experimental basis for revealing the degradation mechanism of F-T cycles on the strength of cement-MK stabilized soil. Based on the Lemaitre's strain equivalence principle, a composite damage variable was derived to comprehensively characterize the coupled effects of F-T cycles and strain rate. A dynamic constitutive model is established based on damage mechanics theory and the Z-W-T model. The results indicate that under the effect of F-T cycles induce progressive porosity increase and aggravated specimen damage. At varying strain rates, the strength of cement-MK stabilized soil decreases with increasing F-T cycles, while the rate of strength reduction gradually diminishes. Under impact loading, both strain rate and the number of F-T cycles significantly reduce the average fragment size of fractured specimens. The modified Z-W-T model effectively predicts the stress-strain relationship of the cement-MK stabilized soil under impact loading.

Lead (Pb) is among the most toxic heavy metals in biological systems and causes toxicity from seed germination to yield formation. High Pb concentrations lead to oxidative damage and impair water relation and nutrition uptake in plants. Rye (Secale cereale L.) is an abiotic stress-tolerant crop, distributed in Eastern and Central Europe. Pb concentration in soils higher than 30 mg kg-1 is commonly toxic to plants. This study investigated the effects of different Pb concentrations [0, 100, 200 and 400 mu M of Pb(NO3)2] on mineral element concentrations (B, Ca, Cu, Fe, K, Mg, Mn, Na and Zn) in rye plants. After 15 days of Pb stress, the levels of mineral elements (B, Ca, Cu, Fe, K, Mg, Zn, Mn and Na), and Pb accumulation were detected using by ICP-OES (Inductively coupled plasma-optical emission spectrometry) in leaves and roots. Under 0, 100, 200 and 400 mu M Pb application, the Pb accumulation varied between 0.005-2.94 and 5.63-13.63 mg kg-1 in leaves, and 0.03-69.34-168.11-329.74 mg kg-1 in roots, respectively. Roots accumulated higher levels of Pb than the leaves. The amounts of Na, Fe and B concentrations reduced, whereas the contents of Ca, K, Mn, Cu, and Zn increased in both leaves and roots in a concentration-dependent manner. The maximum rate of increase or decrease in elemental contents was recorded for 400 mu M Pb-exposed plants. In addition, Mg content increased in leaves, but decreased in roots. Overall, our findings suggest that Pb-exposure causes alterations in mineral element concentrations in a concentration-dependent manner, which could be useful to make risk assessments for Pb pollution in agricultural lands.

This study presents a novel approach to address the current issue of plastic waste in the biosphere, which poses ecological hazards and threatens living beings. Herein, a set of biodegradable composites has been developed through the melt blending of polybutylene adipate-co-terephthalate (PBAT) and rice husk (RH), aiming to discover effective surface modification techniques for enhancing mechanical properties while maintaining biodegradability above 90%. This research studied the diverse surface treatment methodologies applied to raw RH, including alkaline, acetylation, and silane treatments. The novelty of this study lies in its focus on evaluating how these treatments distinctly influence the mechanical properties and biodegradability of RH. Additionally, it seeks to understand the underlying mechanisms driving these performance changes. To further improve the compatibility between hydrophobic PBAT and hydrophilic RH, a compatibilizer such as maleic anhydride (MAH) was added. A range of analytical techniques, including scanning electron microscopy (SEM), tensile testing, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), contact angle measurement, and soil burial test, was employed to investigate the biodegradability of the composites. The results indicate that the PBAT/Silane RH/MAH composite exhibited exceptional mechanical properties, with a tensile strength of 22.49 MPa, a strain at break of 41.83%, and Young's modulus of 187.60 MPa. Furthermore, the composites developed exhibited 90% mass loss during a six-month soil burial test, confirming their remarkable biodegradability. The findings present an innovative and practical solution for utilizing RH waste in a wide range of applications, particularly in the production of molded products such as straws.

(1) Background: Plastic contamination is on the rise, despite ongoing research focused on alternatives such as bioplastics. However, most bioplastics require specific conditions to biodegrade. A promising alternative involves using microorganisms isolated from landfill soils that have demonstrated the ability to degrade plastic materials. (2) Methods: Soil samples were collected, and bacteria were isolated, characterized, and molecularly identified. Their degradative capacity was evaluated using the zone of clearing method, while their qualitative and structural degradative activity was assessed in a liquid medium on poly(butylene succinate) (PBS) films prepared by the cast method. (3) Results: Three strains-Bacillus cereus CHU4R, Acinetobacter baumannii YUCAN, and Pseudomonas otitidis YUC44-were selected. These strains exhibited the ability to cause severe damage to the microscopic surface of the films, attack the ester bonds within the PBS structure, and degrade lower-weight PBS molecules during the process. (4) Conclusions: this study represents the first report of strains isolated in Yucat & aacute;n with plastic degradation activity. The microorganisms demonstrated the capacity to degrade PBS films by causing surface and structural damage at the molecular level. These findings suggest that the strains could be applied as an alternative in plastic biodegradation.

Land reclamation from the sea is increasingly common in coastal areas in China as its urban population continues to grow and the construction of subways in these areas becomes an effective way to alleviate transportation problems. Earth pressure balance shield (EPBS) tunneling in reclaimed lands often faces the problem of seawater erosion which can significantly affect the effectiveness of soil conditioning. To investigate the impacts, in this work, the stratum adaptability of EPBS foaming agents in seawater environments was evaluated based on a series of laboratory tests. The Atterberg limits and vane shear tests were carried out to understand the evolution characteristics of mechanical properties of clay-rich soils soaked in seawater and then conditioned with foams. The results revealed that, for the same foaming agents, the liquid limit and plastic limit of soils soaked in seawater were lower than those in deionized water due to the thinning of bound water films adsorbed on the surface of soil particles. Similarly, soils soaked in seawater had lower shear strength. In addition, the results indicated that the foam volume (FV) produced by foaming agents using seawater as the solvent was slightly higher than that when using the deionized water due to the higher hydration capacity of inorganic salt cations in seawater compared with organic substances. It was also shown that seawater had negative effects on the half-life time (T1/2) and the dynamic viscosity (eta) of foaming agents due to the neutralization reaction between anions in the foaming agents and Na+ present in seawater. The test results also confirmed that 0.5 % of the tackifier (CMC) can alleviate the issue of thin foam films caused by seawater intrusion and improve the dynamic viscosity of foaming agents more effectively, leading to superior resistance to seawater intrusion in EPBS tunnel constructions.