Particle Breakage Characteristics Research Articles

Triaxial behavior of unreinforced and geogrid-reinforced calcareous gravelly sand: Experiment and discrete element modelling

Geogrid reinforcement is a feasible technique for improving the mechanical and deformation behaviors of calcareous gravelly sand that is predominantly distributed in reclaimed foundations as construction materials. However, the shear behavior of geogrid-reinforced calcareous gravelly sand still remains unclear. In this paper, a series of large-scale drained consolidated triaxial compression tests (the specimen 300 mm in diameter by 600 mm in height) were conducted to investigate the effects of confining pressure, moisture content and geogrid inclusion on the mechanical and deformation behaviors of calcareous gravelly sand. The dilation effect, strain-softening behavior, reinforcing effect and particle breakage characteristics of unreinforced and geogrid-reinforced calcareous gravelly sand were comprehensively analyzed and discussed. Additional analysis was also performed from a microscopic perspective using the three-dimensional discrete numerical modelling. The experimental results indicate that calcareous gravelly sand exhibited a greater resistance to strain-softening tendency, and produced a higher susceptibility to crushing under the same input energy than calcareous coarse sand. Geogrid inclusion can effectively mitigate the susceptibility of calcareous gravelly sand to volumetric dilation through constraining the lateral expansion within the reinforced zone, and thus substantially increased the peak shear strength. Moreover, particle breakage appeared to be insensitive to geogrid reinforcement and water content, but increased significantly with increasing confining pressures. The numerical results further indicate that the mechanical response of geogrids was regulated by axial strain and confining pressure. As axial strain was greater than 10%, increased confining pressure resulted in a wider area of stress concentration within the geogrid meshes, and the upper geogrid sustained a greater contact force and tensile strain. The findings in this study are of practical significance for the design and construction of structures in calcareous gravelly sand reinforced with geogrids.

Fractal characteristics of particle breakage on the coral sands–structure interface during ring shear tests

Fractal characteristics of particle breakage on the coral sands–structure interface during ring shear tests

Discussion of “Particle breakage characteristics and grading evolution of calcareous sand under various stress paths”, by Mingxing Luo, Xiaoxuan Liu, Li Zhong and Cai Wu; Marine Georesources & Geotechnology, DOI: 10.1080/1064119X.2024.2302060.

This article aims to elaborate on the primary theme of the published paper in the journal of Marine Georesources and Geotechnology titled "Particle breakage characteristics and grading evolution of calcareous sand under various stress paths." Its purpose is to ensure the integrity of the content, rendering it suitable for consideration as a discussion paper of Mingxing Luo, Xiaoxuan Liu, Li Zhong, and Cai Wu (2024).

Particle breakage characteristics and grading evolution of calcareous sand under various stress paths

Stress path is a key factor affecting the particle breakage of calcareous sand. In this study, the effects of stress path variations on calcareous sand particle breakage were investigated through triaxial compression tests across four distinct stress paths. Additionally, the gradation evolution of calcareous sand during particle breakage was analyzed. Furthermore, the correlation between the total input energy and characteristic particle size was investigated through energy dissipation analysis. The results indicated that the relative breakage index increases gradually with an increase in the maximum deviatoric stress and final volumetric strain, irrespective of the stress path. However, the dilatancy of calcareous sand is related to the relative breakage index as well as the stress path. Notably, the relationship between the relative breakage index and the total input energy can be represented using a power function. A gradation evolution model was formulated based on the results of energy dissipation analysis, and its validity was verified. The results confirmed the model’s effectiveness in predicting the particle breakage evolution in both single-gradation and continuous-gradation calcareous sand specimens, accounting for the effects of the various stress paths.

Crushing and mechanical characteristics of coral sands under various stress paths

Coral sand is known to have stress path dependence and fragility. In this research, a series of drained triaxial tests were conducted to explore stress path effects on the mechanical and particle breakage characteristics of coral sands. Several mechanical characteristics, such as critical state, strength, and dilatancy characteristics were studied. The results revealed that the dilatancy behaviors, stress-strain responses, and crushing of coral sands were strongly affected by consolidation stress and stress path. The critical state lines of coral sands were straight in p‘-q space and e-(p‘/P a)0.44 plane regardless of stress path. Based on these characteristics, a dilatancy equation was derived and validated through test results. The developed dilatancy equation could predict the dilatancy relationships of coral sands under various stress paths.

Influence of the interparticle friction coefficient on the mechanical behaviour of breakable granular materials with realistic shape

Interparticle friction coefficient μ is an important factor affecting the mechanical properties of granular materials. In this study, the influence of μ on the mechanical behavior of granular materials is investigated by DEM. Through 3D scanning and Voronoi tessellations, the breakable particle model with realistic shape is constructed. A series of drained triaxial tests were performed at different μ values. Then, the particle breakage characteristics, including the degree of particle breakage and the breakage mode, were evaluated. In addition, microscopic characteristics, including coordination numbers and contact forces, were examined. Finally, the underlying mechanisms of φc evolution are explained from two perspectives of particle movement and fabric anisotropy. First, the rolling behavior of the particles increases with μ values, leading to a larger average displacement of particles. The influence of particle movement and friction coefficient balance each other, resulting in φc remaining constant when μ⩾0.4. Second, the initial increase of φc is due to the increase of the contact normal anisotropy ac, the normal contact force anisotropy an and the tangential contact force anisotropy at. Subsequently, the constant φc is the result of the decrease of ac and an being compensated by the increase of at.

Experimental Investigation on Particle Breakage Behavior of Marine Silica Sand under High-Stress Triaxial Shear

There is often obvious particle breakage for silica sand under high-stress, which will lead to the bearing capacity reduction and excessive settlement of the foundation. This paper focuses on the particle breakage characteristics of marine silica sand from the East China Sea under high-stress conditions. A series of conventional triaxial tests for silica sand, including consolidated drained (CD) and consolidated undrained (CU) shear tests, were conducted under the confining pressures in the range of 2–8 MPa to investigate the breakage rule during the shearing process. The developments of particle breakage index Br with axial strain ε1 and volumetric strain εv present hyperbolic and linear trends, respectively. A hyperbolic model was adopted to describe the relationship of Br and ε1 and the corresponding model parameters were obtained. The particle breakage index also has a good correlation with the input work per unit volume under various average stresses, regardless of the stress history. Furthermore, the relationship between the fractal dimension and the particle breakage was studied based on the particle size distribution curve. It is concluded that the fractal dimension increases in an up–convex hyperbolic trend with the increase of particle breakage index. The dividing radius for whether the silica sand particles exhibit the fractal features is determined as approximately 0.4 mm. This is anticipated to provide reference and supplementary test data for analyzing sand constitutive models/environments regarding particle crushing.

A coupled FEM-DEM study on mechanical behaviors of granular soils considering particle breakage

Particle breakage often occurs in the fields of geological, geotechnical and hydraulic engineering like rock avalanche, landslides and high earth-rock dam, which affects the design and countermeasures of relevant engineering structures. Investigation of particle breakage’s effect on mechanical behaviors of granular soils has always been the hotspot within the community of particulate materials. In this study, a coupled finite element method (FEM) and discrete element method (DEM) modeling has been developed to tackle boundary value problems (BVPs) related with particle breakage. In the method, the particle breakage simulation is implemented in DEM through the conventional bonded particle modeling (BPM), while the stress–strain characteristics of representative volume element (RVE) captured by DEM is directly transmitted into the FEM solver to avoid the complicated and phenomenological constitutive equations incorporating into particle breakage. As an illustration, we apply the proposed multiscale modeling to investigating mechanical behaviors of quartz sands subjected to particle breakage through the high confining pressure biaxial compression simulation. And effects of particle strength, particle shape and confining pressure on particle breakage characteristics and further mechanical behaviors of quartz sands are also discussed accompanied with the underlying micromechanisms. Results demonstrate that the coupled FEM-DEM modeling can be able to deal with the complex geomechanics problems involving particle breakage.

Experimental investigation on cyclic behavior of geogrid-reinforced coral sand from the South China Sea

The present study provides insight into the cyclic behavior of unreinforced and geogrid-reinforced coral sand. To achieve these goals, stress-controlled undrained cyclic triaxial tests were conducted on medium-dense coral sand with and without geogrid reinforcements. The influence of geogrid reinforcement, cyclic stress ratios, and confining pressure on the deformation, pore pressure, liquefaction resistance, stiffness degradation, and particle breakage characteristics of saturated coral sand was investigated. The results indicated that coral sand reinforced with geogrid increased the liquefaction resistance and decreased the rate of pore pressure accumulation. The effectiveness of the geogrid inclusion on coral sand’s liquefaction resistance was found to be more pronounced under large effective confining pressure and a smaller cyclic stress ratio. Increasing the effective confining pressure increases the liquefaction resistance for both unreinforced and geogrid-reinforced coral sand, whereas increasing the cyclic stress ratios decreases the liquefaction resistance of the unreinforced and reinforced coral sand. The particle breakage was observed to be increased with increasing the effective confining pressure and cyclic stress ratio, and the breakage was more in the reinforced coral sand than the unreinforced coral sand.

Experimental Study on the Effect of Coarse Grain Content on the Dilatancy and Particle Breakage Characteristics of Coarse-Grained Soils

The dilatancy deformation and particle breakage effects of coarse-grained soil have a significant influence on the safety and stability of high earth and rock-fill dams. To study the shear deformation and particle breakage characteristics of coarse-grained soil, four groups of soil sample with different coarse grain contents were to conduct consolidated drained triaxial compression tests by DJSZ-150 large-scale triaxial compression test machine. The results showed that the volume of coarse-grained soil changes significantly under deviation stress. The soil samples underwent positive dilatancy under the confining pressures of 200 kPa and 400 kPa but negative dilatancy under the confining pressures of 600 kPa and 800 kPa. When increasing the coarse grain contents in the soil sample under the same confining pressure, the positive dilatancy was more significant. A three-parameter dilatancy equation of coarse-grained soil considering confining pressure was established, in which the parameter L = 4 could serve as a criterion for whether the coarse-grained soil underwent positive dilatancy. Under the load, the coarse-grained soil showed three particle breakage modes: abrasion, attrition, and fracture. The coarse-grained soil particle size distribution before and after breakage conformed to the fractal characteristics, and the particle breakage rate increased significantly with larger soil particle size fractal dimension differences before and after the test. The coarse grain content and the confining pressure are two important factors affecting the mechanical properties of coarse-grained soil, and they control the shear deformation of soil.

DEM study on the macro- and micromechanical behaviours of breakable granular materials under cyclic loading

The effect of cyclic loading on the macro- and micromechanical behaviours of breakable granular materials was investigated via DEM. Breakable particle models composed of Voronoi cells with realistic shapes were constructed. A series of confined cyclic loading tests were performed at different loading amplitudes. The macroscopic deformation behaviours were investigated in terms of the cumulative plastic strain and dynamic resilience modulus. Then, particle breakage characteristics, including the extent of particle breakage, crack orientation distribution, breakage pattern and correlation between the particle breakage and energy input, were explored. Furthermore, micromechanical results, including the coordination number, sliding contact and contact orientation anisotropy, were examined. It is found that both particle breakage and cumulative plastic strain increase rapidly in the early stage of loading. In the stable state, both showed an S-shaped increase with increasing loading amplitude. This study highlights that particle breakage is one of the main sources of permanent deformation.

A study on the cyclic shear and particle breakage characteristics of the interface between steel and calcareous sand

Research on the mechanical properties of structure–soil interfaces is of great significance to engineering construction in the South China Sea. In this work, an interfacial cyclic shear test between steel and calcareous sand was carried out using self-developed shear equipment, and the macroscopic shear characteristics and particle breakage characteristics were analysed. The results showed that the interfacial peak shear stress under constant stiffness showed more significant weakening characteristics than under constant stress. The calcareous sand showed regular shear shrinkage and dilatancy in a single cycle and was continuously compressed with the number of cycles. The position of the shear stress–normal stress curve moved in the direction of low normal stress with the number of cycles. Under the condition of constant stiffness, the interfacial friction angle at 200kPa increased with the number of cycles, but showed the opposite rule at 1100kPa. The interface shear stiffness under constant stress first decreased and then increased with the number of cycles, while it always decreased under constant stiffness. The relative crushing value increased with the number of cycles; however, the increasing range gradually decreased, and obvious fracture was observed on the surfaces of the broken particles.

Effect of Saturation on Shear Behavior and Particle Breakage of Coral Sand

Coral sand is the main filling material for the island–reef foundation. Under tidal actions, the saturation (Sr) of coral sand layers varies with the specific depths in the reclaimed foundation. Studying the Sr effect of coral sand’s mechanical behaviors is crucial for the stability of the reclaimed foundation of island–reefs. In this study, a “quantitative injection method” was designed to prepare coral sand with saturation ranging from 90% to 100%, and unconsolidated–undrained (UU) triaxial shear tests were conducted on coral sand under different effective confining pressures (σ3′). The results indicated that the stress–strain curves of coral sand under various conditions were of the strain-softening type. When σ3′ = 200, 400, 600, and 800 kPa, the shear strength of coral sand decreased exponentially by 13.1, 9.1, 16.8, and 15.2%, respectively, with the increase in Sr from 90% to 100%. As Sr rose, the internal friction angle (φ) dropped by 3.77°. The cohesion (c) was not significantly affected by Sr compared to φ. In consideration of the physical susceptibility of coral sand to breakage, relative breakage ratio (Br) and modified relative breakage index (Br*) were introduced to evaluate the particle breakage behaviors of coral sand samples with different Sr levels in the triaxial shear process. It was found that Br and Br* increase linearly with increasing Sr; the effect of Sr on the particle breakage of coral sand weakens significantly when σ3′ is sufficiently large. The median particle size (d50) of coral sand decreases with increasing Sr, and presents a negative linear correlation with both Br and Br*. Based on comparing the strength and particle breakage characteristics of coral sand samples with varying Sr levels, this study suggests that 92.5% should be considered as the Sr value of coral sand available for testing.

Review of Particle Breakage Measurement Methods for Calcareous Sand

In order to better understand the particle breakage mechanics and characterization methods of calcareous sand, the particle breakage characteristics of calcareous sand in one-dimensional compression tests, isotropic compression tests, triaxial shear tests, and ring shear tests are reviewed and analyzed. The results show that the mechanism of shear crushing is essentially different from compression crushing. Compared with one-dimensional compression, it is easier to break calcareous sand under triaxial shear. In the shearing process, the particle breakage of calcareous sand will not continue indefinitely. The gradation tends to be stable and controlled by confining pressure and shear strain. The characteristic particle size measurement method for particle breakage is simple and has limitations. The description method using the particle size distribution curve is more comprehensive, but it is impossible to compare the crushing degree of particle with different particle sizes, and a suitable measurement method needs to be proposed.

Characteristics of particle breakage and constitutive model of coarse granular material incorporating gradation evolution

Single particle crushing tests were carried out to research the breakage characteristics of natural rockfill particle. The results showed that the size distribution of broken particles can be described by the normal distribution, and the size distributions of all size fractions converge to a uniform normal distribution after being normalised by the size of the parent particle. Based on the breakage characteristics of rockfill particles, a gradation evolution model was proposed to predict the evolution of the gradation curve of triaxial specimen. This model adopts the loading manner of incremental stress. The correlation among the relative breakage indexes was analysed in terms of the ratio of areas enclosed by the gradation curves and it was found that there is a linear relationship between different indexes. This indicates that there is no essential difference among these indexes from the mathematical point of view. Finally, an elastoplastic constitutive model incorporating the gradation evolution model was developed. This model can predict the stress–strain behaviour and gradation evolution of triaxial specimens of limestone rockfill under the conditions of consolidation, drained and quasi-static shear loading.

Particle breakage behavior in frozen sands during triaxial shear tests based on the energy principle

It is well known that particle breakage in frozen sands continues throughout the triaxial shearing process and is accompanied by irreversible energy dissipation. Accordingly, it is extremely meaningful to investigate the particle breakage characteristics of frozen sands from the perspective of energy dissipation. First, the contact relationships between particles in frozen sands were abstracted as point-to-point and point-to-surface contacts to determine the mechanism of particle breakage under a low stress state. The extra work or energy dissipation attributed to particle breakage results in a higher friction angle, whereas particle breakage suppresses the occurrence of dilatancy, resulting in a lower friction angle. Thus, the friction angle in the samples was continuously modified during testing to incorporate the comprehensive influence of particle breakage and dilatancy. In this study, a modified energy equation for frozen sands was developed considering the continuous variation in the internal friction angle during the loading process. According to this energy equation, the calculated energy dissipation of crushing during shearing is always greater than zero due to the irreversible crushing behavior and increases gradually until it reaches a stable value when no crushing occurs. Finally, a series of cryogenic triaxial compression tests at various temperatures and confining pressures were performed to systematically explore the particle breakage behaviors of frozen soil by using an improved apparatus, and the energy dissipation of frozen soils during the crushing process was further calculated and analyzed based on the improved energy equation. The results demonstrate that the degree of particle breakage is most severe when the axial strain ranges from 1.5% to 2.5% and that energy dissipation presents a hyperbolic trend with axial strain. The results also imply that the particle breakage energy consumption increases when the soil samples are subject to a higher confining pressure, higher shear stress or lower temperature. The aim of this research is to provide a theoretical basis for establishing suitable constitutive models for frozen soils by considering particle breakage from the perspective of energy dissipation.

Mechanical and Hydraulic Properties of Recycled Concrete Aggregates Mixed with Clay Brick Aggregates and Particle Breakage Characteristics for Unbound Road Base and Subbase Materials in Vietnam

The construction industry is one of the key industries with high potential for the circular economy; the promotion of reuse and recycling of construction and demolition waste (CDW) is essential for sustainable urban development. In this study, a series of compaction, California bearing ratio, saturated hydraulic conductivity, and particle breakage tests of well– and poor–graded mixtures of recycled clay brick aggregates (RCBs) and recycled concrete aggregates (RCAs) with maximum aggregate diameters of 19, 25, and 37.5 mm were carried out to examine the practical application of those mixtures to unbound roadbed materials in Vietnam. The experimental results suggest that the maximum amount of RCBs added to RCAs should be less than 30% when applied to unbound roadbed materials. In addition, it was found that the mixing proportions of RCBs and RCAs and the maximum aggregate diameter, gradation of aggregates, and initial moisture condition control the saturated hydraulic conductivity. Further, the particle breakage characteristics under compaction were carefully examined, and it was found that the percentage increment/decrement, as well as a newly introduced method of estimating the mixing proportions of RCAs and RCBs in the fine fraction (<2.36 mm), is effective in understanding the mechanism of particle breakage of RCA and RCB mixtures.

Experimental study on the mechanical behaviors and particle breakage characteristics of calcareous sand from South China Sea under repeated one-dimensional impacts

Experimental study on the mechanical behaviors and particle breakage characteristics of calcareous sand from South China Sea under repeated one-dimensional impacts

Experiment and discrete element modeling of particle breakage in coral sand under triaxial compression conditions

Particle breakage is a major factor that determines the strength and deformation of coral sand. Consolidated drained triaxial compression tests under different confining pressures have been conducted on coral sands as a basis for 3D discrete element simulations, focusing on the particle breakage characteristics. Considering angular breakage and overall breakage in the numerical model, particle breakage is simulated with a fragment replacement method, and the particle size and the equivalent stress are combined as the criterion to judge the occurrence of particle crushing. The validation of the numerical model is proved by reproducing comparable stress-strain relations, evolutions of grain size distribution and relative breakage rate. The overall behavior of the specimen transit from strain softening to strain hardening with the increase in confining pressure from 100 kPa to 400 kPa. Meanwhile, the number of angular breakages increases at a decreasing rate, while the number of overall breakages increase at an increasing rate. This phenomenon implies that overall breakage overwhelms angular breakage and becomes the dominating particle breakage mechanism gradually with increasing confining pressure. Microscopic analyses reveal that higher confining pressure increases the overall contact force, the portion of strong contact force and the coordination number.

DEM simulation of the shear behaviour of breakable granular materials with various angularities

Particle shape is an important factor that affects particle breakage and the mechanical behaviour of granular materials. This report explored the effect of angularity on the mechanical behaviour of breakable granular materials under triaxial tests. Various angular particles are generated using the quasi-spherical polyhedron method. The angularity α is defined as the mean exterior angle of touching faces in a particle model. A breakable particle is constructed as an aggregate composed of coplanar and glued Voronoi polyhedra. After being prepared under the densest conditions, all assemblies were subjected to triaxial compression until a critical state was reached. The macroscopic characteristics, including the shear strength and dilatancy response, were investigated. Then, particle breakage characteristics, including the extent of particle breakage, breakage pattern and correlation between the particle breakage and energy input, were evaluated. Furthermore, the microscopic characteristics, including the contact force and fabric anisotropy, were examined to probe the microscopic origins of the shear strength. As α increases, the peak shear strength increases first and then remains constant, while the critical shear strength generally increases. Assemblies with larger angularity tend to cause more serious particle breakage. The relative breakage is linearly correlated with α under shear loading. Compared with unbreakable particles, the peak shear strength and the critical volumetric strain decline, and the degree of decline linearly increases with increasing α.