Soil Mechanics Research Articles

Temperature effects on adsorption and capillarity water retention mechanisms in constrained unsaturated soils

AbstractThis paper focuses on the impact of elevated temperatures on the adsorptive and capillarity water retention mechanisms of unsaturated soils under constrained (constant volume) conditions. This topic is critical for simulating the thermo-hydraulic behavior of soils in hydrogeological or geotechnical applications, including climate change effects on near surface soils, energy piles or soil borehole thermal energy storage systems in unsaturated soil layers, and buffers for geological nuclear waste repositories. A nonisothermal soil water retention curve (SWRC) that separately considers the temperature-dependency of the key parameters governing adsorptive and capillarity water retention mechanisms and soil physical parameters (e.g., surface tension, contact angle, adsorption capacity, cation exchange capacity, mean cavitation suction, air entry value and equilibrium film thickness) was developed to provide insights into the impact of temperature on water retention over the full suction range. The nonisothermal SWRC was validated using experimental data on high plasticity clays, with a good prediction of temperature effects on adsorption and capillarity water retention mechanisms in constrained unsaturated soils.

A Novel Calculate Model of Shear Deformation and Relative Displacement of Pile–Soil Interface in Warm Frozen Soil Foundation

In permafrost regions with warm frozen soil, the pile foundation is commonly used, but most currently available models for the WFS foundation pile–soil system are either highly empirical or overcomplicated, without a simplified theoretical manner in engineering. This study derives a novel and simplified calculated model of the WFS pile–soil system. The model is formulated in terms of the shear deformation theory and load transfer method based on the rigorous deformation mechanism of the WFS foundation soil around the pile. Considering the different depth soil features and the equilibrium state of the pile–soil system, dividing warm frozen soil foundation into three regions (TPPR, ER, and BPPR) to calculate the Dp and Ds can simply obtain the total displacement of pile under different loads. The results demonstrate that the present theoretical model can well predict the WFS foundation load–displacement response of the pile. The present model provides a simple, practical, and effective approach for the estimation of the load–displacement behavior of piles installed in the WFS foundation.

Triaxial Test and Discrete Element Numerical Simulation of Geogrid-Reinforced Clay Soil

Indoor triaxial tests on geogrid-reinforced clay elucidate the macroscopic changes in soil strength indices post-reinforcement, yet the underlying mechanisms of strength enhancement require further investigation. By conducting indoor triaxial tests and establishing a corresponding discrete element numerical model, we can delve into the fine-scale mechanisms of geogrid-reinforced soil. This includes analyzing changes in fine-scale parameters such as porosity, the coordination number, and contact stress between soil particles. The findings suggest that an increase in the number of geogrid reinforcement layers leads to a more pronounced improvement in peak strength and cohesion, albeit with minimal impact on the internal friction angle of the specimens. Furthermore, analysis of the triaxial test curves of reinforced soils indicates that the stress–strain relationship adheres to the Duncan–Chang model. Parameters derived from this model have been validated against experimental data, confirming their accuracy. The discrete element model was used to analyze the variations in fine-scale parameters such as porosity and coordination number. It revealed that reinforcement reduces the fluctuation amplitude of porosity and significantly increases the number of particle contacts, resulting in a denser soil structure. Further analysis of the change in contact stress between particles in the discrete element model revealed that the contact force between particles increased significantly after reinforcement and that the reinforcement played a role in restraining the soil particles and dispersing the reinforcement stress, which explains the increase in the strength of the mesh-reinforced clays from another perspective. This further elucidates the strength enhancement mechanism in geogrid-reinforced clay, offering a new perspective on the mechanical behavior and strength development of such materials.

Bearing Capacity Characteristic Analysis of Anti-floating Bolts in Unsaturated Soil Based on Mindlin Solution

AbstractBased on Mindlin solution and the theory of unsaturated soil mechanics, the theoretical solutions of shear stress and axial force distribution in the elastic stage of full-length binding-type anti-floating bolts were derived, and the bearing capacity characteristics of such bolts and the influencing factors were analyzed. In this paper, the design parameters of anti-floating anchor in a negative two-floor basement of a commercial square are substituted into the formula derived in this paper. The results show that, in unsaturated soil, the shear stress and axial force of the full-length bonded anti-floating anchor are distributed along the total length of the anchor, but neutral points appear in both of them, which is mainly due to the reduction of the axial force and shear stress of the anti-floating anchor caused by the matric suction. The formula derived in this paper is used to analyze the factors affecting the bearing capacity of anti-floating anchor bolt in unsaturated soil. The results show that: the greater the elastic modulus of soil mass, the greater the peak value of shear stress curve, the closer the peak value is to the head of anchor bolt, and the greater the axial force decline rate. With the increase of anchor solid diameter D, the peak value of shear stress decreases, the peak value moves backward, the neutral point moves forward, the negative shear stress value increases, the decline rate of axial force distribution curve decreases, but the negative axial force increases. With the increase of the additional shear stress τ0, the peak value of the shear stress curve decreases, the peak value moves to the hole of the anchor rod, the neutral point moves to the hole, the negative shear stress increases, the decline rate of the axial force distribution curve increases, and the negative axial force increases.

Analytical and experimental evaluation of two-layered unsaturated sand bearing capacity

Pavement design methods based on principles of unsaturated soil mechanics take into account high soil shear strength due to matric suction resulting in more economical design especially in long roads. In this study, the bearing capacity of two-layer unsaturated sand was investigated using both analytical and experimental methods. At first, using the limit equilibrium method an analytical formula was proposed to determine the bearing capacity of two-layer unsaturated sand in which linear suction profile was considered in soil layers. It should be considered that the constant matric suction distribution assumed by the previous researchers does not show the real profile of matric suction within the soil, sometimes resulting in miscalculated unsaturated bearing capacity. Also, the bearing capacity of two-layer unsaturated poorly graded sand was investigated experimentally in different suctions by a special unsaturated chamber apparatus (UCA) designed for this purpose. The results show more than double increase of unsaturated soil bearing capacity with Sr = 25% compared to saturated soil. The formation of failure wedges in all experiments was investigated by image processing. An acceptable agreement was obtained between the theoretical and experimental bearing capacity results.

Microbiological Mechanisms of Collaborative Remediation of Cadmium-Contaminated Soil with Bacillus cereus and Lawn Plants.

Severe cadmium contamination poses a serious threat to food security and human health. Plant-microbial combined remediation represents a potential technique for reducing heavy metals in soil. The main objective of this study is to explore the remediation mechanism of cadmium-contaminated soil using a combined approach of lawn plants and microbes. The target bacterium Bacillus cereus was selected from cadmium-contaminated soil in mining areas, and two lawn plants (Festuca arundinacea A'rid III' and Poa pratensis M'idnight II') were chosen as the target plants. We investigated the remediation effect of different concentrations of bacterial solution on cadmium-contaminated soil using two lawn plants through pot experiments, as well as the impact on the soil microbial community structure. The results demonstrate that Bacillus cereus promotes plant growth, and the combined action of lawn plants and Bacillus cereus improves soil quality, enhancing the bioavailability of cadmium in the soil. At a bacterial suspension concentration of 105 CFU/mL, the optimal remediation treatment was observed. The removal efficiency of cadmium in the soil under Festuca arundinacea and Poa pratensis treatments reached 33.69% and 33.33%, respectively. Additionally, the content of bioavailable cadmium in the rhizosphere soil increased by up to 13.43% and 26.54%, respectively. Bacillus cereus increased the bacterial diversity in the non-rhizosphere soil of both lawn plants but reduced it in the rhizosphere soil. Additionally, the relative abundance of Actinobacteriota and Firmicutes, which have potential for heavy metal remediation, increased after the application of the bacterial solution. This study demonstrates that Bacillus cereus can enhance the potential of lawn plants to remediate cadmium-contaminated soil and reshape the microbial communities in both rhizosphere and non-rhizosphere soils.

A new experimental setup for the determination of drying soil–water characteristic curve and coefficient of permeability using the continuous evaporation method and osmotic tensiometers

Soil-water characteristic curve (SWCC) and coefficient of permeability (k) are amongst the most crucial soil properties in unsaturated soil mechanics for soil moisture conservation. The direct measurement and prediction of such properties are important to engineering applications, but they are complicated. This study developed a new experimental setup (the OT permeameter) using osmotic tensiometers (OTs) and the continuous evaporation method. The proposed OT permeameter could directly measure SWCC and k up to 1000 kPa suction within one to two weeks. Moreover, the proposed setup is fully automated and data processing was minimal. In addition, a new general equation has been developed to predict and best fit the unsaturated k measurement. The proposed equation uses a minimal number of parameters that carry physical meaning and provides an intuitive and easy way to predict and best-fit k measurement. The accuracy and robustness of both the proposed OT permeameter and prediction equation were evaluated using published data and experimental data from this study.

Unsaturation triggers specific adsorption performance of water films in the clay nanopores

Soil is typically unsaturated, with water films covering the soil particles playing a crucial role in soil mechanics, structure, and element transport. However, the unusual behavior of these water films and the underlying mechanisms are not yet fully understood. This study, which used molecular dynamics methods, sheds light on the distinct interactions between water films and clay surfaces under unsaturation. At the water-mineral interface, water molecules formed a layered structure, while they rearranged as a meniscus as the unsaturation extent increased. On the other hand, unsaturation had a significant impact on the location of water molecules at the water-vapor interface, but only a limited effect at the water-mineral interface. The water’s orientational ordering and hydrogen bonding interactions were significantly affected by changes in relative humidity (RH). Based on the distance-dependent diffusion coefficient, the water molecules within the water film were classified into three types: WT1 (< 5 Å) had faster diffusivity at higher RH, WT2 (5–6 Å) had comparable diffusivity at any RH, and WT3 (> 6 Å) had faster diffusivity at intermediate RH. This classification was supported by the retention dynamics analysis. The specific behaviors mentioned above, which are associated with unsaturation, are closely linked to Na+ hydration. This is because the interaction between water and Na+ is more pronounced than the interaction between water and minerals or Cl−. The results indicate that unsaturation triggers specific adsorption behaviors of water films that cover the clay surfaces. These behaviors should be considered in interfacial processes and environmental engineering.

Recovery of Rare Earth Elements from Ion-Adsorption Deposits Using Electrokinetic Technology: The Soil Conductivity Mechanism Study

Rare earth elements (REEs) are essential raw materials for modern industries but mining them has caused severe environmental issues, particularly the recovery of heavy REEs (HREEs) from ion-adsorption deposits (IADs). Very recently, an emerging technology, electrokinetic mining (EKM), has been proposed for the green and efficient recovery of REEs from IADs. However, the conduction mechanism of the weathering crust soil, which is also a prerequisite for EKM, remains unclear, making the EKM process unpredictable. Here, we systematically investigated the conductivity of weathering crust soil in the presence of light REEs (LREEs, i.e., La3+ and Sm3+) and HREEs (Er3+ and Y3+), respectively. Results suggested that the voltage was dynamically and spatially redistributed by the movement of REEs and water during EKM, and the conventional assumption of the linear distribution of voltage leads to an inaccurate description of soil voltage. We proposed an improved Archie’s equation by coupling the mechanisms of liquid phase and solid-liquid interface conduction, which can predict soil conductivity more precisely. Moreover, the extended Archie’s equation is able to recalculate the voltage distribution at distinct times and spaces well during EKM. More importantly, the water content in field-scale weathered-crust soils can be retrieved by the newly proposed Archie’s equation, which helps optimize the leaching wells and improve the recovery rate of REE. This study focuses on the conduction mechanism of weathering crust soil, which provides a theoretical basis for better use of the EKM technology and promotes mining efficiency fundamentally.

Bearing capacity of shallow foundations: a focus on the depth factors in combination with the respective N-factors

The ongoing refinement of bearing capacity equations remains pivotal in soil mechanics and foundation engineering, reflecting its critical role in ensuring design efficacy and construction safety. This study conducts a thorough evaluation of classical bearing capacity methods—Terzaghi, Meyerhof, Vesic, and Hansen—and methods included in various design standards, such as EN1997:2004, prEN1997:2023, GEO, AASHTO, FHWA, and API. It explores the performance and applicability of these approaches, identifying areas for potential improvement. In response to identified challenges, the paper proposes the integration of a unified depth factor. This new factor is designed to be applicable across all N-terms, providing a more versatile and accurate tool for bearing capacity predictions. Unlike the original depth factors unique to each method, which may not fully address complex soil and footing conditions, the unified depth factor is developed to enhance prediction accuracy for a wide range of conditions, including both flexible and rigid footings under varying flow rules (ψ = 0 and ψ = φ). This depth factor corrects for modeling errors, emphasizing the importance of pairing the correct set of N-factors with their corresponding depth factor. By offering a singular depth factor that aligns with the outcomes of finite element analysis, this paper not only simplifies the computational process but also enhances the accuracy of bearing capacity predictions across a diverse range of soil conditions and footing types. The comparative analysis, based on finite element analysis, validates the proposed method’s effectiveness, showcasing its potential to significantly refine foundation design practices by comparing it with both traditional and newly developed depth factors.

Soil mechanics principles for modelling railway track performance

Predicting the performance of railway track is difficult owing to the complex and repeated nature of the loading, the many millions of cycles applied over the life of the structure, the need to characterise the often-infinitesimal rate of accumulation of plastic settlement, and the importance of differential settlements in the along-track direction, which can adversely impact train ride and passenger comfort. These come in addition to the usual soil mechanics challenges of reproducing in a constitutive model the real behaviour of soil and soil-like materials such as railway ballast. Degradation of the geomaterials comprising the trackbed and the underlying ground or earthwork owing to mechanical and environmental effects is a further concern. The paper discusses these issues and explores the application of fundamental soil mechanics principles and advanced constitutive models to understanding and quantifying their effects on railway track and trackbed performance. Recommendations for future research are made.

A framework for estimating the matric suction in unsaturated soils using multiple artificial intelligence techniques

AbstractImplementation of the state‐of‐the‐art understanding of the mechanics of unsaturated soils into geotechnical engineering practice is partly limited due to the lack of quick, reliable, and economical techniques for matric suction measurement. Matric suction is one of the key stress state variables that significantly influences the hydro‐mechanical behavior of unsaturated soils. In this paper, to address this objective, two artificial intelligence (AI) models were developed for estimating matric suction in unsaturated soils based on the particle swarm optimization support vector regression (PSO‐SVR) and multivariate adaptive regression spline (MARS) algorithms. The results suggest that both these models can reasonably estimate matric suction. Compared to the MARS model, the PSO‐SVR model can achieve higher accuracy. Nonetheless, the MARS model facilitates the sensitivity analysis and the selection of essential inputs. A novel integrated framework is proposed and validated, leveraging the strengths, and alleviating the limitations of the PSO‐SVR and MARS algorithms for reliable and rapid estimation of matric suction in the range of 0–1500 kPa for low plastic soils (0 &lt; Ip ≤ 7). Six inputs are required to use this model successfully; some can be measured using conventional laboratory tests, and others can be calculated from mass‐volume relationships.

Finite Element Analysis of Combined Bearing Characteristics of Pile–Soil Interaction in Composite Foundation

Composite foundations have been widely used and promoted in practical engineering applications. However, research on the joint-bearing mechanism of piles and soil within composite foundations is still not comprehensive enough. This paper proposes a method for calculating the additional internal forces of piles and soil within composite foundations. Based on a three-dimensional finite element analysis, this study investigates the variation patterns of the stress, displacement, and additional internal forces of piles and soil in the depth direction under the action of upper loads when using friction piles and end-bearing piles. This research aims to reveal the bearing performance of piles and soil. The results showed that, under the same conditions and due to the presence of end-bearing effects, the internal forces experienced by the entire pile body of the end-bearing piles were more uniform, exhibiting significant advantages in resisting deformation and being able to withstand larger loads. Additionally, the diffusion mechanism of the vertical forces, stresses, and displacements of piles and soil is discussed. Due to the negative frictional resistance of soil and the influence of pile end-bearing effects, the distribution of internal forces and the displacements of piles and soil exhibited different characteristics. This study provides a scientific reference for the theoretical analysis and design of composite foundations.

Enhancing Soil Resilience to Climatic Wetting‐Drying Cycles Through a Bio‐Mediated Approach

AbstractClimatic wetting‐drying cycles exacerbated by climate change can trigger several weakening mechanisms in surface soils, potentially leading to instability and failure of slopes and earthen structures. This study proposes a bio‐mediated approach based on microbially induced calcite precipitation (MICP) to increase soil resilience to wetting‐drying cycles. To explore its viability and the underlying mechanisms, we conducted a series of laboratory tests on clayey soil that underwent six wetting‐drying cycles. The tests were conducted with different treatment methods to investigate the effect of treatment sequence and cementation solution concentration. After MICP treatment, the initial evaporation rate, surface crack ratio during drying, and total soil weight loss during rainfall erosion were reduced by up to 32%, 85%, and 90%, respectively. Spraying the cementation solution first in the MICP treatment sequence proves more effective in improving soil water retention capacity. On the other hand, initiating the sequence with the bacterial solution demonstrates a more pronounced effect in reducing soil desiccation cracks and erosion. Microstructure analysis reveals that the content and distribution of CaCO3 precipitation are the major factors controlling the effectiveness of MICP for the cementation of clayey soil. Employing MICP can minimize the carbon footprint and contribute to developing environmentally friendly solutions for soil improvement in regions affected by climatic wetting‐drying cycles.

Unveiling the regulatory mechanism of poly-γ-glutamic acid on soil characteristics under drought stress through integrated metagenomics and metabolomics analysis.

It is of utmost importance to understand the characteristics and regulatory mechanisms of soil in order to optimize soil management and enhance crop yield. Poly-γ-glutamic acid (γ-PGA), a stress-resistant amino acid polymer, plays a crucial role in plant drought stress resistance. However, little is known about the effects of γ-PGA on soil characteristics during drought treatments. In this study, the effects of different forms of γ-PGA on soil texture and basic physical and chemical properties under short-term drought conditions were investigated. Furthermore, the impact of γ-PGA on the microbial community and metabolic function of maize was analyzed. Under drought conditions, the introduction of γ-PGA into the soil resulted in notable improvements in the mechanical composition ratio and infiltration capacity of the soil. Concurrently, this led to a reduction in soil bulk density and improved soil organic matter content and fertility. Additionally, metagenomic analysis revealed that under drought conditions, the incorporation of γ-PGA into the soil enhanced the soil microbiota structure. This shift led to the predominance of bacteria that are crucial for carbon, nitrogen, and phosphorus cycles in the soil. Metabolomics analysis revealed that under drought treatment, γ-PGA affected soil metabolic patterns, with a particular focus on alterations in amino acid and vitamin metabolism pathways. Correlation analysis between the soil metagenome and metabolites showed that microorganisms played a significant role in metabolite accumulation. These results demonstrated that γ-PGA could improve soil characteristics under drought conditions and play an important role in soil microorganisms and microbial metabolism, providing further insights into the changes in soil characteristics under drought conditions.

Microscale Mechanical Behaviour Evaluation of Unsaturated Granular Soils via 4D in situ Triaxial Test on μ-CT

Owing to the complex structure and stress history of unsaturated soils, the micro-mechanism of effective stress theory in unsaturated soil mechanics remains unelucidated. In this study, we developed a miniature triaxial test apparatus for a micro-focus computed tomography (μ-CT) scanning system for the microscopic study of the mechanical behaviour of unsaturated soil. By comparing the results from the developed mini-triaxial test device system with those from a conventional triaxial device, its experimental accuracy was verified. Micron-level high-resolution CT images of sheared specimens at different strain stages were obtained using the device for in situ suction-control triaxial compression 4D (3-Dimensional+Dynamic) tests with a μ-CT scanning system. The multiscale evolution behaviours of the physical parameters (porosity and degree of saturation) of the specimens corresponded to the stress–strain relationship revealed by the in situ test. Triaxial shearing drains out the pore water, and the decomposition of the largest water clusters causes the quantity of small-volume liquid clusters to increase, shifting the distribution of the interfacial areas. The degree of saturation scale indicates the presence of liquid bridges within the shear band that provide interparticle cementation effect and thus enhance the global strength of unsaturated granular soil specimens.

Study on strain localization of frozen sand based on uniaxial compression test and discrete element simulation

Strain localization has always been an important subject in frozen soil mechanics and engineering. To evaluate the development of local strain and the formation of shear bands in frozen soil, uniaxial compression tests have been conducted on frozen sand at various temperatures and particle grades. The strain localization evolution law of the frozen soil is analyzed utilizing the digital image correlation (DIC) method. The test results reveal that the entire process of shear band generation, development, and formation in frozen soil can be well captured. Within the testing temperature and particle grade range in this study, in comparison to particle grade, temperature exerts a more pronounced influence on the shear band angle which increases as temperature decreases. It is discovered that the width of the shear band increases with the decrease in temperature and the increase in mean particle diameter d50. Subsequently, a discrete element method (DEM) model is developed to examine the microscopic mechanical characteristics of frozen sand in uniaxial compression tests. The reliability of the DEM model is verified through comparative analysis with test results. Besides, the development law of the strain localization of the frozen soil obtained by the numerical simulation is revealed based on the quantitative analysis of the rotational angle, bonding state, and displacement of the soil particle during the shearing process.

Feasibility and mechanism of high alumina cement-modified chlorine saline soil as subgrade material

Soil salinization is a serious problem during ground improvement and foundation construction around the coastal region. This study used high alumina cement (HAC) as a soil stabilisation agent to modify the coastal chlorine saline soil as roadbed backfilling materials. In addition, Ordinary Portland cement (OPC), slaked lime (SL) and fly ash (FA) were used to better the understanding of the chlorine fixation and roadbed performance. The microstructures of different hydration products were investigated through the utilization of the X-ray diffraction and scanning electron microscope equipped with an energy dispersion spectrometer. The HAC-SL-modified soil depicts that the aluminium and calcium phases are beneficial to the formation of Friedel’s salt and hydration products. The optimal chlorine fixation is approximately 20.5% at 6% HAC-SL incorporation (3% of HAC and 3% SL). At the early stage of curing, the strength of the HAC-treated soil is high. However, with a prolonged curing period, there is a slight decrease in the strength because the porosity will increase during the transformation of metastable CAH10 and C2AH8 into stable and dense C3AH6. This evolution can be prevented by incorporating SL to enrich calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H). Furthermore, it is of key importance to mention that HAC reaction is quick, therefore, the compaction should be undertaken instantly to ensure the road performance.

Warming inhibits HgII methylation but stimulates methylmercury demethylation in paddy soils

Inorganic mercury (HgII) can be transformed into neurotoxic methylmercury (MeHg) by microorganisms in paddy soils, and the subsequent accumulation in rice grains poses an exposure risk for human health. Warming as an important manifestation of climate change, changes the composition and structure of microbial communities, and regulates the biogeochemical cycles of Hg in natural environments. However, the response of specific HgII methylation/demethylation to the changes in microbial communities caused by warming remain unclear. Here, nationwide sampling of rice paddy soils and a temperature-adjusted incubation experiment coupled with isotope labeling technique (202HgII and Me198Hg) were conducted to investigate the effects of temperature on HgII methylation, MeHg demethylation, and microbial mechanisms in paddy soils along Hg gradients. We showed that increasing temperature significantly inhibited HgII methylation but promoted MeHg demethylation. The reduction in the relative abundance of Hg-methylating microorganisms and increase in the relative abundance of MeHg-demethylating microorganisms are the likely reasons. Consequently, the net Hg methylation production potential in rice paddy soils was largely inhibited under the increasing temperature. Collectively, our findings offer insights into the decrease in net MeHg production potential associated with increasing temperature and highlight the need for further evaluation of climate change for its potential effect on Hg transformation in Hg-sensitive ecosystems.

Combination Mechanism of Soil Dissolved Organic Matter and Cu2+ in Vegetable Fields, Forests and Dry Farmland in Lujiang County

Dissolved organic matter (DOM) serves as a critical link in the migration and transformation of heavy metals at the soil–solid interface, influencing the migration behaviour and transformation processes of Cu2+ in soil. There have been studies on the combination mechanisms between DOM and Cu2+ in paddy soils. However, the adsorption/complexation and redox processes between DOM and Cu2+ in other agricultural soil types (such as dry farmland and vegetable fields) are unclear. In order to reveal the combination process of DOM with Cu in different agricultural soil types and the dynamic changes in chemical behaviour that occur, this study analysed the variability of DOM components and structure in three soils using three-dimensional fluorescence spectroscopy and X-ray photoelectron spectroscopy. In addition, the priority order of different DOM compounds in combination with Cu and the change process in relation to the Cu valence state in the soil of Lujiang County, Anhui Province, was revealed based on laboratory experiments. The results showed that the composition of soil DOM was mainly composed of humic-like and fulvic-like substances with a clear terrestrial origin and that the organic matter showed a high degree of decomposition characteristics. The results indicated that the composition of soil DOM is mainly composed of humic and fulvic acid-like substances, and they have obvious characteristics of terrestrial origin. In addition, the soil organic matter showed high decomposition characteristics. The complex stability constants (lgKM) of humic acid-like substances with Cu2+ follow the order of forest land (lgKM = 5.21), vegetable land (lgKM = 4.90), and dry farmland (lgKM = 4.88). The lgKM of fulvic acid-like substances with Cu2+ is in the order of dry farmland (lgKM = 4.51) and vegetable land (lgKM = 4.39). Humic acid-like substances in soil DOM combine preferentially with Cu2+, showing a stronger chelating affinity than fulvic acid-like substances. Cu2+ complexes mainly include hydroxyl, phenolic hydroxyl and amino functional groups are included in soil DOM, accompanied by redox reactions. In comparison to dry farmland, the soil DOM in forest and vegetable fields undergoes more intense redox reactions simultaneously with the chelation of Cu2+. Therefore, the application of organic fertilisers to vegetable and forest soils may lead to uncertainties concerning the fate of heavy metals with variable chemical valence. These results contribute to a deeper understanding of the interaction mechanisms between DOM and Cu2+ in agricultural soils.