Conventional materials necessitate a layer-by-layer rolling or tamping process for subgrade backfill projects, which hampers their utility in confined spaces and environments where compaction is challenging. To address this issue, a self-compacting poured solidified mucky soil was prepared. To assess the suitability of this innovative material for subgrade, a suite of performance including flowability, bleeding rate, setting time, unconfined compressive strength (UCS), and deformation modulus were employed as evaluation criteria. The workability and mechanical properties of poured solidified mucky soil were compared. The durability and solidification mechanism were investigated. The results demonstrate that the 28-day UCS of poured solidified mucky soil with 20% curing agent content reaches 2.54 MPa. The increase of organic matter content is not conducive to the solidification process. When the curing temperature is 20 degrees C, the 28-day UCS of the poured solidified mucky soil with curing agent content not less than 12% is greater than 0.8 MPa. The three-dimensional network structure formed with calcium silicate hydrate, calcium aluminate hydrate, and ettringite is the main source of strength formation. The recommended mud moisture content is not exceed 85%, the curing agent content is 16%, and the curing temperature should not be lower than 20 degrees C.

A comprehensive series of tests, including dynamic triaxial, monotonic triaxial and unconfined compressive strength (UCS) tests, were carried out on reconstituted landfill waste material buried for over twenty years in a closed landfill site in Sydney, Australia. Waste materials collected from the landfill site were treated with varying percentages of cement, and both treated and untreated specimens were investigated to evaluate the influence of cement treatment. The study examined the dynamic properties of cement-treated landfill waste, including cumulative plastic deformation, resilient modulus, and damping ratio, and also analysed the impact of cyclic loading on post-cyclic shear strength in comparison to pre-cyclic shear strength. The UCS tests and monotonic triaxial tests demonstrated that untreated specimens subjected to monotonic loading exhibited a progressive increase in strength with rising axial strain, whereas cement-treated specimens reached a peak strength before experiencing a decline. During cyclic loading, with the inclusion of cement, a significant reduction in cumulative plastic deformation and damping ratio was observed, and this reduction was further enhanced with increasing cement content. Conversely, the resilient modulus showed substantial improvement with the addition of cement, and this enhancement was further amplified with increasing cement content. The formation of cementation bonds between particles curtails particle movement within the landfill waste material matrix and prevents interparticle sliding during cyclic loading, leading to lower plastic strains and damping ratio while increasing resilient modulus. Post-cyclic monotonic testing revealed that cyclic loading caused the partial breakage of the cementation bonds, resulting in reduced shear strength. This reduction was higher on samples treated with lower cement content. Overall, the findings of the research offer crucial insights into the possibility of cement-treated landfill waste as a railway subgrade, laying the groundwork for informed design decisions in developing transport infrastructure over closed landfill sites while using landfill waste materials available on site.

Deep-rooted maize plants utilize water and nutrients more effectively, particularly in compacted soil. However, the mechanisms by which different maize genotypes adjust root angles in response to compaction remain underexplored. We conducted a two-year study (2021-2022) on silty loam soils in the North China Plain. We tested two genotypes of maize [one with naturally deep roots (DR) and another with shallow roots (SR)] in compacted (C) and non-compacted (NC) soil. Soil compaction impeded shoot growth in both genotypes; however, DR exhibited better growth than SR. Under compacted conditions, DR maintained steeper root angles and demonstrated superior mechanical strength with larger root cortex areas (increased by 60 %) and stele (increased by 92 %), as well as higher cellulose concentration (up to 146 %). Notably, PIEZO1 gene expression increased significantly (up to 242 %) in DR under compaction, suggesting its role in root structural enhancement, unlike in SR where it remained unchanged. These findings underscore the importance of genetic, anatomical, and biochemical adaptations in maize roots, facilitating their resilience to soil compaction. Such insights could inform the breeding of maize genotypes that are better adapted to diverse soil conditions, potentially boosting agricultural productivity.

Iron pipes connected by bell-spigot joints are utilized in buried pipeline systems for urban water and gas supply networks. The joints are the weak points of buried iron pipelines, which are particularly vulnerable to damage from excessive axial opening during seismic motion. The axial joint opening, resulting from the relative soil displacement surrounding the pipeline, is an important indicator for the seismic response of buried iron pipelines. The spatial variability of soil properties has a significant influence on the seismic response of the site soil, which subsequently affects the seismic response of the buried iron pipeline. In this study, two-dimensional finite element models of a generic site with explicit consideration of random soil properties and random mechanical properties of pipeline joints were established to investigate the seismic response of the site soil and the buried pipeline, respectively. The numerical results show that with consideration of the spatial variability of soil properties, the maximum axial opening of pipeline joints increases by at least 61.7 %, compared to the deterministic case. Moreover, in the case considering the variability of pipeline-soil interactions and joint resistance, the spatial variability of soil properties remains the dominant factor influencing the seismic response of buried iron pipelines.

The incorporation of PCMs in energy piles holds significant potential for revolutionising thermal management in construction, making them a crucial component in the development of next-generation systems. The existing literature on PCM-integrated energy piles largely consists of isolated case studies and experimental investigations, often focusing on specific aspects without providing a comprehensive synthesis to guide future research or practical applications. To date, no review has been conducted to consolidate and evaluate the existing knowledge on PCMs in energy piles, making this review the first of its kind in this field. Up until now, this gap in research has limited our understanding of how PCM configurations, thermal properties, and integration methods impact the thermal and mechanical performance of these systems. Through thoroughly analysing the current research landscape, this review discovers key trends, methodologies, and insights. The methodology used here involved a systematic search of the existing SCI/SCIE-indexed literature to ensure a structured review. Based on the SLR findings, it is evident that current research on PCMs in energy piles is focused on improving thermal efficiency, heat transfer, and compressive strength. Furthermore, precise adjustments in melting temperature significantly impact efficiency, with PCM integration boosting thermal energy extraction by up to 70 % in some cases, such as heating cycles, and saving up to 30 % in operational costs. PCMs also reduce soil temperature fluctuations, improving structural integrity through minimising axial load forces. However, challenges remain, including reduced mechanical strength due to voids and weak bonding, high costs, and complexities such as micro-encapsulation. We acknowledge that there are gaps in addressing certain key factors, including thermal diffusivity; volume change during phase transitions; thermal response time; compatibility with construction materials; interaction with soil, creep, and fatigue; material compatibility and durability; and the long-term energy savings associated with PCM-GEP systems.

The hydraulic effect of plant roots reduces precipitation infiltration and enhances shallow slope stability. However, after root death and decay, soil permeability increases while water-retention capacity decreases. The time-varying mechanisms governing the hydraulic properties of root-soil composites after root decay remain unclear. This study examines the evolution of soil pore structure following root decay. A time-varying soil water retention curve (SWRC) model was developed to characterize changes in water-retention capacity. Additionally, a time-varying saturated infiltration coefficient model and a permeability coefficient prediction model were established to describe variations in hydraulic properties. A one-dimensional soil column infiltration test was conducted on root-soil composites at different stages of root decay to investigate the time-dependent changes in hydraulic properties. The reliability of the proposed models was validated using experimental results. The findings indicate the following: After root death, root biomass, diameter, length, and number decreased with increasing decay time, stabilizing after four months. Root decay led to a reduction in root volume ratio, which altered soil structure and enhanced the permeability of root-soil composites. Longer decay periods increased soil porosity, modifying the soil water characteristic curve and reducing water-retention capacity. Creeping roots decayed more significantly than fibrous roots due to their distinct morphological traits, making changes in hydraulic properties more pronounced in the topsoil. Therefore, plant root decay negatively affects soil hydraulic properties by continuously altering soil pore structure. These findings provide a crucial foundation for understanding the time-dependent mechanisms of hydraulic property variations in root-soil composites during plant root decay.

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 study developed a novel geopolymer (RM-SGP) using industrial solid wastes red mud and slag activated by sodium silicate, aiming to remediate composite heavy metal contaminated soil. The effects of aluminosilicate component dosage, alkali equivalent, and heavy metal concentration on the unconfined compressive strength (UCS), toxicity leaching characteristics, resistivity, pH, and electrical conductivity (EC) of RM-SGP solidified composite heavy metal contaminated soil were systematically investigated. Additionally, the chemical composition and microstructural characteristics of solidified soil were analyzed using XRD, FTIR, SEM, and NMR tests to elucidate the solidification mechanisms. The results demonstrated that RM-SGP exhibited excellent solidification efficacy for composite heavy metal contaminated soil. Optimal performance occurred at 15 % aluminosilicate component dosage and 16 % alkali equivalent, achieving UCS >350 kPa and compliant heavy metal leaching (excluding Cd in high-concentration groups). Acid/alkaline leaching tests revealed distinct metal behaviors: Cu/Cd decreased progressively, while Pb initially declined then rebounded. Microstructural analysis indicated that RM-SGP generated abundant hydration products (e.g., C-A-S-H, N-A-S-H gels), which acted as cementitious substances wrapping soil particles and filling and connecting pores, thereby increasing the soil's compactness and improving the solidification effect. Furthermore, heavy metal ions were solidified through adsorption, encapsulation, precipitation, ion exchange, and covalent bond et al., transforming their active states into less bioavailable forms, proving novel insights into the remediation of composite heavy metal contaminated soils and the resource utilization of industrial solid wastes.

The vadose zone acts as a natural buffer that prevents contaminants such as arsenic (As) from contaminating groundwater resources. Despite its capability to retain As, our previous studies revealed that a substantial amount of As could be remobilized from soil under repeated wet-dry conditions. Overlooking this might underestimate the potential risk of groundwater contamination. This study quantified the remobilization of As in the vadose zone and developed a prediction model based on soil properties. 22 unsaturated soil columns were used to simulate vadose zones with varying soil properties. Repeated wet-dry cycles were conducted upon the As-retaining soil columns. Consequently, 13.9-150.6 mg/kg of As was remobilized from the columns, which corresponds to 37.0-74.6 % of initially retained As. From the experimental results, a machine learning model using a random forest algorithm was established to predict the potential for As remobilization based on readily accessible soil properties, including organic matter (OM) content, iron (Fe) content, uniformity coefficient, D30, and bulk density. Shapley additive explanation analyses revealed the interrelated effects of multiple soil prop-erties. D30, which is inter-related with Fe content, exhibited the highest contribution to As remobilization, fol-lowed by OM content, which was partially mediated by bulk density.

Mastering the mechanical properties of frozen soil under complex stress states in cold regions and establishing accurate constitutive models to predict the nonlinear stress-strain relationship of the soil under multi-factor coupling are key to ensuring the stability and safety of engineering projects. In this study, true triaxial tests were conducted on roadbed peat soil in seasonally frozen regions under different temperatures, confining pressures, and b-values. Based on analysis of the deviatoric stress-major principal strain curve, the variation patterns of the intermediate principal stress, volumetric strain and minor principal strain deformation characteristics, and anisotropy of deformation, as well as verification of the failure point strength criterion, an intelligent constitutive model that describes the soil's stress-strain behavior was established using the Transformer network, integrated with prior information, and the robustness and generalization ability of the model were evaluated. The results indicate that the deviatoric stress is positively correlated with the confining pressure and the b-value, and it is negatively correlated with the freezing temperature. The variation in the intermediate principal stress exhibits a significant nonlinear growth characteristic. The soil exhibits expansion deformation in the direction of the minor principal stress, and the volumetric strain exhibits shear shrinkage. The anisotropy of the specimen induced by stress is negatively correlated with temperature and positively correlated with the bvalue. Three strength criteria were used to validate the failure point of the sample, and it was found that the spatially mobilized plane strength criterion is the most suitable for describing the failure behavior of frozen peat soil. A path-dependent physics-informed Transformer model that considers the physical constraints and stress paths was established. This model can effectively predict the stress-strain characteristics of soil under different working conditions. The prediction correlation of the model under the Markov chain Monte Carlo strategy was used as an evaluation metric for the original model's robustness, and the analysis results demonstrate that the improved model has good robustness. The validation dataset was input to the trained model, and it was found that the model still exhibits a good prediction accuracy, demonstrating its strong generalization ability. The research results provide a deeper understanding of the mechanical properties of frozen peat soil under true triaxial stress states, and the established intelligent constitutive model provides theoretical support for preventing engineering disasters and for early disaster warning.