The discrete element method (DEM) has demonstrated significant advantages in simulating soil-tool interaction and an appropriate contact model notable affected the simulation accuracy. The accuracy of numerical simulation is compromised due to the variations in soil properties when tillage implements are employed in clay-moist soil conditions. This study aims to establish a discrete element model of clay-moist soil based on the Edinburgh Elasto-Plastic Adhesion (EEPA) contact model. Calibration tests using a combination of direct shear tests and cone penetration tests were conducted to identify sensitive parameters that need to be calibrated in the model and analyze the effects of each parameter. The results indicated that contact plasticity ratio and surface energy had significant influence on representing the mechanical properties of clay-moist soil. Then, by utilizing scanning technology to acquire furrow shape data, soil bin test was conducted to validate the reliability of the calibration parameters. Using sensitive parameters as variables, the actual value of clay-moist soil with a moisture content of 33 % as the target value obtained from experimental tests. The optimal combination was: the coefficient of static friction of 0.45, the coefficient of rolling friction of 0.18, and the surface energy of 27.95 J.m-2, the contact plasticity ratio of 0.59. The relative error between the simulated draft force value and the actual measured value was 7.98 %, and the relative errors in the furrow type parameters did not exceed 5 %. The accuracy of the calibration results was verified through comparative analysis of simulation and empirical results. This study provides a scientific approach for employing DEM in modeling clay-moist soil-tool interaction.

In cold regions, the strength and deformation characteristics of frozen soil change over time, displaying different mechanical properties than those of conventional soils. This often results in issues such as ground settlement and deformation. To analyze the rheological characteristics of frozen soil in cold regions, this study conducted triaxial creep tests under various creep deviatoric stresses and established a corresponding Discrete Element Method (DEM) model to examine the micromechanical properties during the creep process of frozen clay. Additionally, the Burgers creep constitutive model was used to theoretically validate the creep deformation test curves. The research findings indicated that frozen clay primarily exhibited attenuated creep behavior. Under low confining pressure and relatively high creep deviatoric stress, non-attenuated creep was more likely to occur. The theoretical model demonstrated good fitting performance, indicating that the Burgers model could effectively describe and predict the creep deformation characteristics of frozen clay. Through discrete element numerical simulations, it was observed that with the increase in axial displacement, particle displacement mainly occurs at both ends of the specimen. Additionally, with the increase in creep deviatoric stress, the specimen exhibits different deformation characteristics, transitioning from volumetric contraction to expansion. At the same time, the vertical contact force chains gradually increase, the trend of particle sliding becomes more pronounced, and internal damage in the specimen progresses from the ends toward the middle.

The delayed breakage of particles significantly affects the long-term mechanical properties of rockfill materials. This study examines the effects of particle strength dispersion on the distribution of time-dependent strength using fracture mechanics and probabilistic methods. Subsequently, the distribution of normalized maximum contact force (NMCF), defined as the ratio of the maximum contact force to instantaneous strength, for specimens with uniform particle size is derived using extreme value theory and Discrete Element Method (DEM). Based on this analysis, the probabilities of delayed breakage in rockfill specimens over various time intervals are calculated using a joint probability delayed breakage criterion. The feasibility of the proposed method is validated by comparing theoretical calculation with DEM triaxial creep simulation results that accounted for particle breakage. The findings offer innovative tools and theoretical insights for understanding and predicting the particle delayed breakage behavior of rockfill materials and for developing macro-micro creep crushing constitutive models.

The macroscopic mechanical properties of granular systems largely depend on the complex mechanical responses of force chains at the mesoscopic level. This study offers an alternative to rapidly identify and predict force chain distributions under different stress states. 100 sets of gradation curves that effectively represent four typical continuous gradation distributions are constructed. Numerical specimens corresponding to these gradation curves are generated using the discrete element method (DEM), and a dataset for deep neural network training is established via biaxial compression numerical simulations. The relationship between particle distribution characteristics and force chain structure is captured by the Pix2Pix conditional generative adversarial network (cGAN). The effectiveness of the generated force chain images in reproducing both particle gradation and spatial distribution characteristics is verified through the extraction and analysis of pixel probability distributions across different color channels, along with the computation of texture feature metrics. In addition, a GoogLeNet-based prediction model is constructed to demonstrate the accuracy with which the generated force chain images characterize the macroscopic mechanical properties of granular assemblies. The results indicate that the Pix2Pix network effectively predicts and identifies force chain distributions at peak stress for different gradation

The mechanical behaviour of soil subject to shear loading or deformation is typically considered either completely drained or undrained. Under certain conditions, these drained and undrained scenarios can represent boundaries on the allowed volumetric strain. There is growing interest in exploring the response under intermediate conditions where partial drainage is allowed, particularly in the development of new approaches to mitigate the risk of liquefaction induced failure and the design of off-shore structures. This study uses the discrete element method (DEM) to investigate the effect of partial drainage conditions on the mechanical behaviour of spherical assemblies. Samples with different interparticle friction values are isotropically compressed and then subjected to undrained, drained, and partially drained triaxial shearing. The partially drained conditions are simulated in the DEM samples by applying a controlled volumetric strain that is a fraction of the drained volumetric strain. Results on loose samples indicate that allowing drainage enhances peak shear resistance and can also prevent liquefaction. Moreover, dense samples show a substantial increase in shear resistance when small changes in drainage and volumetric strain take place. The peak stress ratio and the stress ratio at the phase transformation point are insensitive to the drainage level. There is a linear correlation between the state parameter and the drainage level at the peak stress ratio and the phase transformation point. This observation could be used to trace partially drained stress-paths and could also aid the development of uncoupled constitutive models that account for drainage effects.

This paper analyzed the influence of the inherent anisotropy of sand on active and passive arching by simulating the trapdoor emplying the discrete element method (DEM). The inherent anisotropy is reflected by the bedding plane angle alpha of particles. The granular material constitutive responses are captured on representative volume elements (RVEs). A new modeling method is employed to prepare particle specimens, aiming to obtain a more uniform soil model. The results indicate that the discrete element method can simulate the influence of the inherent anisotropy of granular material on the evolution of soil arching. An asymmetric arching evolution phenomena is observed in the alpha other than 0 degrees or 90 degrees cases, which leads to obvious asymmetric deformation and stress distribution in the soil. As the filling height increases, this phenomenon becomes more and more obvious. From a microscopic perspective, the reorientation of the contact normal fabric caused by particle rotation is the main reason for the differences in soil arching evolution with different alpha. This study provides a theoretical basis for predicting ground deformation failure caused by underground engineering activities and changes in surrounding environmental conditions.

Construction and Demolition Wastes (CDW) serves as an effective filler for highway subgrades, demonstrating commendable performance characteristics. The efficient utilization of CDW not only contributes to environmental sustainability but also yields significant economic benefits. This study employs discrete element simulation to develop a triaxial sample model comprising particles with four distinct levels of sphericity. By varying the combinations of sphericity, brickconcrete ratio, and void ratio, triaxial simulation tests are conducted, and the critical state soil mechanics framework is applied to fit the critical state line (CSL) of the samples. The results indicate that sphericity, brick-concrete ratio, and void ratio substantially influence the macroscopic mechanical properties of CDW. Notably, as sphericity increases, the peak deviatoric stress of the samples decreases, and significant volume deformation occurs. The slope of the CSL in the q-p ' plane diminishes, while the slopes of both forms of the CSL in the e-log p ' plane increase. Furthermore, a decrease in the brick-concrete ratio enhances the anti-deformation and compressive capacities of the samples. As the brick-concrete ratio decreases, both the slopes and intercepts of the CSL in the e-log p ' plane exhibit an upward trend. Conversely, an increase in the void ratio leads to a reduction in the overall strength and anti-deformation capacity of the specimens, an increase in the compressibility of the specimen volume, an elevation of the CSL slope on the q-p ' plane, and a gradual increase in both the slope and intercept of the semilogarithmic form of the CSL on the e-log p ' plane, as well as a gradual increase in the slope of the power-law form of the CSL.

The instability and collapse mechanisms of tunnels in deep-buried marine soil-rock mixture (SRM) strata remain poorly understood, posing significant challenges to engineering safety. This study employs a discrete element method (DEM) to establish an S-RM model, integrating ball particles and rblock blocks to simulate soil and rock, respectively. The deformation evolution, shear band formation, porosity variation, force chains, and anisotropy of S-RM under varying stress release rates are systematically investigated, with emphasis on rock content, water content, and rblock types (rubble and cobble). The results reveal that tunnel excavation reduces radial interparticle contact forces, inducing convergent squeezing deformation, while tangential forces increase, forming a soil arch dominated by horizontal force chains. Higher rock content enhances shear resistance and accelerates soil arch formation but intensifies dilatancy under high stress release, expanding collapse zones. Elevated water content increases lateral pressure coefficients, promoting earlier arch formation, yet reduces interparticle bond strength and rock anti-slip capacity, leading to premature shear failure. Cobbles, whose long axis tends to rotate in the slip direction, exhibit weaker shear resistance and lower dilatancy than rubble, thereby increasing soil arch instability. Crucially, shear band evolution and force chain fracture at side walls disrupt arch integrity, triggering progressive collapse. These micro-mechanisms elucidate the coupled effects of stress redistribution, particle interactions, and material heterogeneity on S-RM failure. Suggestions for construction control include minimizing excavation footage, implementing timely support, and reinforcing sidewalls with feet-lock bolts to stabilize soil arches. This work advances the theoretical framework for disaster mitigation in deep-buried S-RM strata, offering a DEMbased paradigm for predicting and controlling tunnel instability.

This paper presents a comprehensive study on the evolution of the small-strain shear modulus (G) of granular materials during hydrostatic compression, conventional triaxial, reduced triaxial, and p-constant triaxial tests using 3D discrete element method. Results from the hydrostatic compression tests indicate that G can be precisely estimated using Hardin's equation and that a linear correlation exists between a stress-normalized G and a function of mechanical coordination number and void ratio. During the triaxial tests, the specimen fabric, which refers to the contact network within the particle assembly, remains almost unchanged within a threshold range of stress ratio (SR). The disparity between measured G and predicted G, as per empirical equations, is less than 10% within this range. However, once this threshold range is exceeded, G experiences a significant SR effect, primarily due to considerable adjustments in the specimen's fabric. The study concludes that fabric information becomes crucial for accurate G prediction when SR threshold is exceeded. A stiffness-stress-fabric relationship spanning a wide range of SR is put forward by incorporating the influences of redistribution of contact forces, effective connectivity of fabric, and fabric anisotropy into the empirical equation.

Using the discrete element method (DEM) to simulate the rice machine transplanting operation is important for assessing the plant injury and optimizing the rice transplanter performance, while the DEM flexible model establishment that can accurately reflect the mechanical properties of the rice blanket seedling root blanket is an important foundation. Based on the root blanket's stratification and the root system structure's measurement and statistics, a new method for root blanket flexible modeling was proposed in this study. Firstly, the Hertz-Mindlin with bonding V2 contact model was used to establish substrate I (SI), substrate II (SII), substrate III (SIII), stemroot combination (SRC), and netted layer (NL) flexible models, respectively, and the model parameters were calibrated and determined by angle of repose (AOR), direct shear, and mechanical tests. The calibration results showed that the deviations of AOR simulated values for SI and SII were both less than 1.5 %, and the deviations of shear strength simulated values were both less than 4 %. Secondly, the shear characteristics of SI and SII were determined by direct shear test. The results showed that the physical and simulated shear stress-displacement relationship curves of SI and SII were basically the same; the hair roots mainly relied on the cohesive between them and the substrate to improve the substrate strength; the fitted lines of simulated shear strength and normal stress of SI and SII were in high agreement with these of the measured values; the deviations of the simulated cohesion and internal friction angle were both less than 5 %. After that, the Hertz Mindlin with JKR V2 contact model was used between SRC and substrate. The interfacial surface energy of the root blanket and the bonding parameters of SIII were calibrated by stem, half-SRC, and SRC pulling-out tests layer by layer. The calibration results showed that the deviation of the maximum pulling-out force of SRC was 5.83 %, verifying that the model could accurately simulate the intertwining effect of the crown roots. Finally, the flexible model of the root blanket was verified by cutting, curling, and tensile tests. The simulated test results were consistent with the trends of the physical test results; the deviations of the maximum cutting resistance of front cutting and side cutting were both within 8 %, the error percentage range of the marked points height was 0.35 % to 17.16 %, and the deviation of the maximum tensile force was 9.22 %, indicating the good feasibility of the modeling method and accuracy of the flexible model. The results of this study lay a foundation for the DEM simulation of the rice machine transplanting operation. They can also provide a reference for the numerical simulation of other multiplant root-soil complexes.