Granular Matter最新文献

The profile is a crucial characteristic of a ballast particle. It is important to characterize the uncertainties of three-dimensional ballast particle profiles and to determine the effects of these profiles on the dynamic performance of ballast bed. In this study, the spherical harmonics method was employed to achieve efficient reconstruction of the three-dimensional profiles of 300 ballast particles, which were obtained by performing indoor scanning. The relationships between elongated or flaky particles and the various orders of spherical harmonics functions were proven. The findings demonstrate that, when the spherical harmonics order exceeded 15, the errors in the volume, surface area and sphericity of the reconstructed particles were less than 5% compared to real particles. Furthermore, the spherical harmonics spectra approximately conformed to a gamma distribution, for which the average coefficient of determination (({R}^{2})) was 0.95. The second order relative spherical harmonics frequency significantly influenced the major ballast shape, which was considered to be cubic when this frequency was less than 0.17. Then, by utilizing the Nataf transformation, a joint probability density function of the spherical harmonics frequencies was established, which enabled probabilistic characterization and rapid random generation of the 3D profiles of ballast particles. Direct shear tests revealed that the proposed model exhibited an error of only 3%; in contrast, models that employed spherical particles or single type particles showed substantially higher errors that could reach 66%. Finally, a ballast bed was developed to analyze the effects of elongated and flaky particles on the lateral resistance of ballast bed and the sleeper acceleration receptance. The results indicated that the lateral resistance could increase by up to 30% as the proportions of elongated and flaky particles increased, while the sleeper acceleration receptance below 500 Hz not changed.

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This study investigates the influence of grain size distribution (GSD), initial water content (w_i), and aggregates shape on the segregation behavior of granular materials subjected to vertical vibration. A series of controlled laboratory experiments was conducted using twelve different GSDs at initial moisture contents ranging from 0 to 10%. The results show that both the extent and continuity of the GSD significantly affect the occurrence of water upwelling and segregation of solids. Sub-rounded aggregates exhibit higher levels of segregation than sub-angular aggregates. Water content plays a dual role: increasing moisture reduces segregation up to an optimal saturation threshold, beyond which segregation increases again. No water migration was observed when the maximum particle size (D_max) was less than 2.5 mm, and the fines content (D < 0.08 mm) remained below 10%. However, materials with discontinuous gradations and fines contents exceeding 10% exhibited upward migration of fines and localized liquefaction when the degree of saturation exceeded 50%. The findings also highlight the critical role of the intermediate particle fraction (0.08 mm < D < 5 mm) in controlling saturation variations, beyond the influence of the coarsest and fines fractions. Although restrictive grain size specifications can help limit segregation, the study emphasizes the need for appropriate construction practices and compaction methods to maintain homogeneity in granular layers.

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This research examines the quasi-static and high-strain-rate characteristics of granular soil types: crushed and natural sands with a siliceous nature, using the Triaxial and Split Hopkinson Pressure Bar (SHPB) methods, respectively. The effects of particle shape, gradation, moisture content of sand, and loading strain rate on mechanical response pre-and post-breakage have been extensively investigated. The results from the current study demonstrated that natural sand possessed superior strength, attributed to its well-graded distribution and effective particle interlocking, whereas crushed sand exhibited lower strength and failure attributed to its angular particles and inadequate packing. Natural sand, which is characterised by its finer grains and higher density, exhibited improved energy absorption and strain rate sensitivity. The effect of moisture content varied across the sands, influencing compressibility and peak strength based on saturation levels and incident pressure. Scanning electron micrograph results pre-post breakage showed that particle shape and gradation of the sands strongly affect the break and evolve under dynamic load. The findings from the current work provide valuable insights for the response of granular materials subjected to extreme loading under man-made and natural disasters.

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Granite residual soil is widely distributed in southern China, with high permeability, large porosity, and weak cementation. It is highly susceptible to erosion and landslides under heavy rainfall conditions. To enhance the mechanical properties of biocemented granite residual soil, laboratory tests were conducted to investigate the effects of various cementing solution parameters. Different grouting volumes, concentrations, and cycles of biocementation are compared in this study. Results indicated that high single-grouting volumes and high concentrations impeded the improvement of mechanical properties, while increasing the number of cycles was much more effective. Grouting volume was determined to be 1.05–1.2 times of porosity with a concentration of about 1.0 mol/L. Biocemented granite residual soil mainly gained increased shear strength through the increase of cohesive strength, while the internal friction angle played a minor role. The micro- and meso-pores dominated in the evolution of porosity, and its repair effectively influenced the mechanical properties. Moreover, filling pores and cementation of the soil particles improved the loose, porous, and weak bonding state of the soil. Improvement in mechanical properties could be considered varied and caused by the bridging effect, agglomeration, and coating at the microstructural interfaces. Vaterite formed under high solution concentrations and large injection volumes is prone to transformation into calcite, and the volumetric shrinkage associated with this phase transition leads to a deterioration in mechanical performance. This study offers valuable insights into the mechanisms and effectiveness of improving the mechanical properties of biocemented granite residual soil.

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Robots capable of manipulating cohesive materials would be beneficial in a variety of complex construction tasks. To discover principles by which robotic systems can effectively manipulate entangled granular media, we develop a robophysical platform for interaction with media composed of u-shaped particles. This robotic platform uses environmental signals to autonomously coordinate excavation, transport, and deposition of material. We test the effect of material initial conditions by characterizing robot performance in two different material compaction states, and observe as much as a 75% change in transported mass depending on initial material compressive loading. This large difference suggests the functional role that properties such as packing and geometric cohesion play in excavation and manipulation. To better understand these properties, we develop an apparatus for tensile testing of the geometrically cohesive media, which reveals how entangled material strength depends strongly on initial compressive loading. These results rationalize the variation observed in robotic performance and point to future directions for better understanding robotic interaction with entangled materials.

Gas suction during the concrete pumping process causes a transition from constant flow to unsteady flow, seriously compromising boom stability. Therefore, this study investigated the characteristics of unsteady flow in the different pipelines of a pump truck. Firstly, based on the C40 concrete properties, a pipeline fluid domain geometric model was established to verify the grid independence. Then, a three-phase flow mathematical model was constructed, including gas-liquid phase control equations, a solid particle motion equation, and a laminar flow model. Gas and liquid phase flows were simulated using Fluent, and the interaction between solid particles was simulated using Rocky. The flow characteristics of straight, elbow, and combined pipes were simulated using a coupling method of computational fluid dynamics (CFD) and discrete element method (DEM). Finally, a comparison is made based on numerical simulations of the effects of different pipeline structures and pumping parameters on concrete flow characteristics. The results indicate that increasing the gas volume fraction reduces pressure in both straight pipes and elbows, and decreases the excitation force in straight pipes. However, the excitation force in the elbow remains unchanged. Notably, the excitation force in the straight pipe peaks at a gas volume fraction of 30%. Increasing the attitude angle of the straight pipe raises the pressure but decreases the excitation force. Increasing the curvature radius of the elbow will increase the pressure, but it has little effect on the excitation force.

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To elucidate the coupled breakage–deformation mechanisms of soft rock residuals in large-scale embankment applications, this study focuses on phyllite materials from the Kangluo Expressway project in Gansu Province, China. A combined experimental and numerical investigation was conducted under varying gradation conditions to examine interactions between particle breakage and deformation. Talbot continuous gradation curves (n = 0.30, 0.50, 0.7) and corresponding single-sized gradations were evaluated. A total of 400 single-particle crushing tests were performed to derive the Weibull modulus m and characteristic strength σ₀ through statistical fitting. One-dimensional confined compression tests were conducted in a steel cylinder (150 mm diameter, 300 mm height). To quantify the relative breakage ratio, one-dimensional confined compression tests were performed in a rigid steel cylinder (150 mm diameter, 300 mm height). The specimen was subjected to a stepwise axial stress path, which initiated from a minimal seating stress (regarded as 0 kPa for reference) and advanced through discrete increments to a peak of 15 MPa. Complementary discrete element simulations, implemented in PFC3D, employed a Fragment Replacement Method (FRM) to model particle breakage. The model stipulated that when the octahedral shear stress of a particle surpassed its specific fracture threshold, the mother particle would be instantaneously replaced by an assembly of 14 Apollonian sub-particles. This replacement was governed by the strict conservation of both mass and volume, ensuring the physical realism of the simulated breakage process. The simulation results aligned closely with experimental data regarding stress–strain behavior and the correlation between Talbot gradation and breakage ratio. These findings provide experimental validation and theoretical guidance for utilizing soft rock waste and calibrating discrete element models.

Photoelasticity has become a widely used tool for quantifying stresses in quasi-two-dimensional experimental granular flows, providing valuable insight into the behaviour of inter-particle forces, typically for quasi-static flow geometries. Here we analyse high-inertial photoelastic collisions, and investigate the particle-scale dynamic response, relaxation due to viscoelasticity, and boundary deformation. Through high-speed experiments using impulsive loading of particles, we find that standard photoelastic theory fails under high-inertial conditions. In this work, we extend the photoelastic methodology to accurately capture forces acting on polymeric particles experiencing rapid changes in momentum. Our experiments highlight the influence of viscoelastic properties of our polymer particles, and we identify two key timescales to describe the viscoelastic relaxation. Importantly, we report the existence of fossil photoelasticity, showing that the photoelastic signal at a given moment in time may not accurately depict the instantaneous forces acting on a particle. In this work, we introduce a modified theoretical framework that accounts for particle deformation and so allows greater insight into the inter-particle contact mechanics of experimental granular systems. Our distributed-force approach to deriving photoelastic fringe patterns enables stress distributions along deformed particle boundaries, rather than through infinitesimal areas, to be extracted from experimental images.

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In this work, we perform high-speed experiments to subject photoelastic particles to highly inertial forces. We find that current theory fails to capture the inertial photoelastic response, and we provide an updated mathematical formulation to account for these unbalanced forces. We also observe important viscoelastic properties of photoelastic particles and develop a model to describe their leading-order relaxation behaviour. Finally, we introduce a framework to utilise particle boundary deformation, providing unprecedented insight into the spatial distribution of stresses acting on photoelastic particles.

The damage of marine soft clay during the loading process is closely related to the microstructure changes. Triaxial shear tests and field emission scanning electron microscope (FESEM) tests were carried out on the marine soft clay in the fourth layer of Shanghai. It focuses on analyzing the effect of microscopic clay aggregates break-up on the damage of Shanghai marine soft clay during the shearing process, and revealing the damage mechanism. The results show that: during the shear process, the Shanghai marine soft clay stress–strain curves show obvious strain hardening phenomenon, and the secant modulus undergoes attenuation, and the maximum attenuation degree reaches 90.9%. The microstructure mainly undergoes clay aggregate cementation destruction, clay aggregate break-up and disintegration into smaller aggregates or dispersed clay particles. The relative breakage Br of clay aggregates increases gradually with the increase of confining pressure and strain, with a maximum value of 0.24. It can be calculate by the proposed equation with confining pressure and strain. The damage variable D is proposed based on the relative breakage Br, the D has a negative exponential relationship with strain. And the secant modulus damage evolution equation of Shanghai marine soft clay is developed, which can accurately describe the modulus damage evolution of Shanghai marine soft clay in the shear process. It can further deepen the understanding of the damage of Shanghai marine soft clay.

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Granular materials, ubiquitous in geophysics, chemical engineering, biophysics and soft matter physics, present unique challenges for optical imaging due to their opaque and heterogeneous nature. This perspective paper provides a comprehensive overview of opportunities in Light Sheet Microscopy (LSM) techniques for imaging granular materials, emphasizing refractive index matching as a critical tool for visualizing internal deformations and flow dynamics. By matching the refractive indices of solid particles and surrounding fluids, researchers can create “transparent soils” or analogous systems, enabling detailed examination of particle interactions, strain fields, and fluid flow. To comprehensively introduce opportunities for future research, the review explores the evolution of LSM, from early broadband light sources to modern laser and LED-based systems, highlighting advancements in wavefront shaping and contrast generation through scattering and fluorescence. The paper also surveys some innovative approaches for LSM and index matching, such as Sephadex spheres and cryolite. Emerging techniques, such as wavefront shaping and three dimensional imaging with event cameras, are presented as promising avenues for future research. Additionally, the review connects granular imaging to biological systems, demonstrating its relevance for studying microbial motility, biofilm growth, and tissue engineering. This perspective paper aims to guide and inspire researchers in selecting and refining LSM techniques for advancing the understanding of complex particulate systems.

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Light Sheet Microscopy offers opportunities for granular materials science.