Degree Of Particle Breakage Research Articles

Elastic-viscoplastic model for coarse-grained soil considering particle breakage

This paper presents a novel elastic-viscoplastic constitutive model for reproducing the time-dependent behaviour of coarse-grained soil considering particle breakage, by integrating the Unified Hardening (UH) model, the elastic-viscoplastic (EVP) model and the overstress theory. The relationship between the degree of particle breakage and the loading rate is established, and the state variables associated with the critical state of coarse-grained soil are derived to jointly consider both time and particle breakage. A new three-dimensional elastic-viscoplastic constitutive model is then constructed through combining the one-dimensional viscoplastic hardening parameter with a secondary consolidation coefficient considering particle breakage. The proposed model requires 19 parameters and it can well describe the influence of time-dependency and particle breakage to the shear, dilatancy, and compression behaviours of coarse-grained soil with various confining pressures or initial void ratios. Comparisons between the model predictions and experimental data are employed to validate the capability of the proposed model to replicate the time-dependent behaviour of coarse-grained soil.

An extended hypoplastic constitutive model considering particle breakage for granular material

We present a hypoplastic model for the granular material to account for the particle breakage effect. The degree of particle breakage is expressed by a relative breakage ratio, which evolves with the input energy during the loading process. The critical state line of the model is related to the relative breakage ratio to reflect the influence of particle breakage on the mechanical behavior of soil. The model performance is demonstrated by comparing the model simulations with the experimental results under different test conditions.

Performance of silica bricks with ferrosilicon nitride as the mineralizer

Novel silica bricks were made of crystalline silica with ferrosilicon nitride as the mineralizer. The phase, microstructure, pore characteristics and high-temperature properties of the novel silica bricks prepared by adding 1%, 1.5% and 2% ferrosilicon nitride were characterized. The results showed that, compared to conventional silica bricks (with mineralizers of calcium hydroxide and iron scale), the novel silica bricks with the addition of ferrosilicon nitride contained less calcium oxide, less residual quartz and more tridymite. The ferrosilicon nitride was gradually oxidized to form SiO2 and Fe2SiO4 during the firing stage of the silica bricks. After adding ferrosilicon nitride, the degree of particle breakage was reduced, and the pore size of interconnected pores increased. With the increase in ferrosilicon nitride content, the silica brick structure gradually densified. The silica brick sample with 2% ferrosilicon nitride achieved better creep resistance at high temperature (1550 °C, 0.2 MPa), but the refractoriness under load of the bricks was slightly reduced by using ferrosilicon nitride as a mineralizer. An optimization model of ferrosilicon nitride as a mineralizer was established.

Effect of particle breakage on the behavior of soil-structure interface under constant normal stiffness condition with DEM

Previous studies show that extensive particle breakage occurs at the soil-structure interface, which may influence the shear strength, but a corresponding comprehensive micro-mechanical analysis, particularly with constant normal stiffness (CNS), is missing. In this study, a series of interface shear tests under CNSs are simulated with the discrete element method (DEM) to understand the role of particle breakage at the interface. Through a rigorous calibration process, the interface model in DEM is first validated with identifying micro-mechanical parameters. Then, by modifying the reference tensile strength of particles, the effect of particle breakage on the behavior of soil-structure interface is quantitatively investigated. All results demonstrate that, particle breakage decreases the dilation, normal stress, shear stress, and shear zone thickness in the interface shear test; particle breakage decreases the peak friction angle while increases the residual friction angle at the interface; and particle breakage decreases soil anisotropy at the interface. In addition, the degree of particle breakage is increased by normal stiffness. The findings of this study may provide deeper insights on the role of particle breakage at the interface with CNS and allow engineers to have a better estimation of the interface strength.

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.

Experimental Investigation of the Mechanical Properties of Methane Hydrate–Bearing Sediments under High Effective Confining Pressure

A significant increase in effective stress can be induced in hydrate-bearing reservoirs when the depressurization method is applied. A series of drained triaxial shear tests were performed on hydrate-bearing sediments with various hydrate saturations to investigate their mechanical characteristics under effective confining pressures of up to 20 MPa. The results show that significant particle crushing of the host sand occurs during shearing under high pressures, and there is no remarkable effect of hydrate saturation on the degree of particle breakage. As the effective confining pressure increases, the stress–strain curves of the hydrate-bearing specimen transformed from strain-softening to strain-hardening. The peak stress ratio and internal friction angle of the sediments gradually decrease and tend to be constant with the increased confining stress, whereas the cohesion in hydrate-bearing sediments exhibits an increasing tendency. The critical state line (CSL) of hydrate-bearing sediments in the e-lnp′ space under low-to-high effective confining pressures intersects with the normal consolidation line under the same hydrate saturation. Furthermore, the CSL moves upward and rotates clockwise as the hydrate saturation increases.

Effect of particle shape on the liquefaction resistance of calcareous sands

The irregular particle shape is the significant feature of calcareous sands. It is known that calcareous sands generally show a higher liquefaction resistance than that of quartz sands, but the contribution of particle shape to the liquefaction resistance has not been well understood. In this paper, the particle shapes of calcareous sand, quartz sand and steel ball were quantitively assessed. Then, undrained monotonic and cyclic simple shear tests were conducted to investigate the influence of particle shape on the liquefaction resistance. The particle size and shape before and after simple shear were compared to assess the particle breakage. It is found that the degree of particle breakage is quite small, the surface grinding is the main mode, and the particle shape keeps almost unchanged during cyclic simple shear. Irregular sand particles show slow accumulation of excess pore pressure and need more cycles to trigger liquefaction in cyclic tests. It also shows the liquefaction resistance has a good linear correlation with the overall regularity of sand particles. Based on the fitting parameters, the liquefaction resistance of sand samples with different particle shapes can be directly obtained by the provided overall regularity of the sand particles.

Coke generation and conversion behavior of pulverized coal combustion

Preheating combustion is a promising novel low-nitrogen technology. The coke generation and conversion behavior in the preheater and combustion chamber are studied in this paper. The particle size distribution, apparent morphology, specific surface area, pore structure distribution and combustion reactivity of the coke can be analyzed respectively with the particle size analyzer, scanning electron microscope, automatic specific surface area analyzer and Raman spectrometer. The results show that the preheated char generated by the preheating process has some merits: the particle size is smaller, specific surface area is larger, the pore structure is more developed and combustion reactivity is higher. In the down-fired combustor, the degree of particle breakage, apparent morphology, specific surface area and pore structure are influenced by the combustion reaction intensity. Combining the analysis of the graphite stable structure and the active carbon defect structure, the combustion reactivity order of four samples is: 100 mm > 400 mm > preheated char> 900 mm. This paper provides experimental support and theoretical analysis for this technology to achieve deep control of nitrogen.

Monotonic behavior of interface shear between carbonate sands and steel

The characteristic of interface shear between carbonate sands and steel is important for the design of onshore/offshore foundations in coral reef deposit. By using an interface ring shear apparatus, the influences of particle size, normal stress, steel roughness and shear displacement on the interface shear strength were studied in this paper. During the tests, the particle movement localized in the deformation band was observed and the degree of particle breakage was evaluated. The test results showed that under the effect of large displacement interface shear (≥ 1 m), a significant particle breakage occurred in the thin zone near the interface, and the roughness of steel interface decreased accordingly. The relative smooth steel surface shows small interface friction angle without dilation phenomenon during shearing, while higher roughness leads to higher interface strength due to stress dilation. It was also found that there was a kind of particle size discontinuity in the shear zone. Particle breakage is main reason for the increase in interface friction angle in large displacement shear. A new dimensionless parameter was proposed to consider the influences of particle breakage and interface roughness on the mobilization of interface strength between sands and steel. It is recommended that the influence of fine particles embedded into steel interface should be considered in large displacement shear for carbonate sands.

Discrimination of Particle Breakage below Pile Tip after Model Pile Penetration in Sand Using Image Analysis

Particle breakage is a common phenomenon in granular soils and has been well observed during laboratory and in-situ pile studies. In this paper, an image analysis approach was developed to investigate the particle breakage behavior below a flat-ended pile tip, with special attention given to the location of particle breakage. The color difference between the original silica sand (light gray) and its coated surface (black) allows particle breakage to be distinguished based on the gray level variation. Larger gray values corresponded to a higher degree of breakage that occurred within the target area, which provides a new approach for quantitative assessment of the particle breakage extent. First, sequential images of the subsoil at different depths below a loaded pile tip were digitally recorded, and the degree of particle breakage was subsequently evaluated based on the gray level of the images. Then, the layered images at different depths were assembled to form a quasistereoscopic graph, and the slice image at any profile could be obtained. Accordingly, the zone of particle breakage below a flat-ended pile tip was graphically illustrated. The results of this study are beneficial for further clarifying the mechanism of particle breakage and provide a fundamental basis for accurate assessment of the ground-bearing capacity considering soil crushability.

Numerical Simulation Study on Flow and Fracture of Granular Materials

Flow and fracture of granular materials under external loads is a complex mechanical process, and the research on its law is still in the exploratory stage. In this paper, the flow and fracture law of granular materials is taken as the research object, and numerical algorithm compilation and program development are combined to study. Taking full advantage of the existing algorithms and developing new ones based on the existing DEM theory, a numerical simulation program for the flow and fracture of granular materials is developed. The flow and fracture process of concrete spherical granular system with diameter of 4 cm under loading rate of 70 mm/min and end of loading of 50 kN is taken as an example to verify the simulation program. At the same time, the loading experiment of the concrete spherical particle system under the same simulation conditions was also carried out. The simulation results are compared with the experimental results in three aspects: the generation location of the particle system, the relationship between the whole load and displacement, and the degree of particle breakage. The results show that the numerical simulation is in good agreement with the experimental results, which verifies the reliability of the numerical algorithm and the simulation program, and can provide support for the study of the flow and fracture process of granular materials.

Effect of Particle Shape and Confining Pressure on Breakage and Deformation of Artificial Rockfill

The rockfill exhibits a substantial amount of particle breakage when subjected to higher range of stresses. The deformations of rockfill under such excessive stresses often lead to failure and cannot be ignored. The degree of particle breakage is related to the type of the material as well as the particle shape. Based on this, artificially simulated rockfill materials with three different aggregate shapes (prism, cube, and cylinder) were prepared by cement paste-casting method. Through a series of medium-sized triaxial shear tests, the effects of confining pressure and particle shape on the fracture characteristics of the artificial rockfill and its secant modulus were investigated. The useful relationships between particle sphericity and roundness with deformation modulus and particle breakage rate were proposed.

Particle breakage of artificially crushable materials subject to drained cyclic triaxial loading

Upon cyclic loading, particle breakage of constituent granular materials occurs when the resulting local stresses exceed their strength, which has a significant influence on the deformation of the embankment, foundation and pavement structures. In this study, the artificially crushable materials were tested to investigate the particle breakage properties of these structures when subjected to drained cyclic triaxial loading. Twelve sets of samples were tested at the confining pressures of 100, 125, 150 and 175kPa and a frequency of 1.0Hz using a GCTS triaxial system. The cyclic test results indicate that at the same confining pressure, the residual volumetric strain increases with decreasing maximal deviatoric stress qmax at a given ratio of the number of cycles (N) to the number of cycles of failure (Nf). The cumulative crushing ratio Rcc decreases with increasing qmax, leading to a reduction in Nf. The internal frictional angle decreases with increasing Rcc, and Rcc increases with increasing Nf. Furthermore, the confining pressure, maximal cyclic deviatoric stress and N have significant influences on the degree of particle breakage, which leads to volumetric contraction during the cyclic loading process. Finally, the resilient modulus at failure increases linearly with increasing Rcc.

Stress-dilatancy of Zipingpu gravel in triaxial compression tests

Experimental investigations of the dilatancy and particle breakage of gravelly material from the Zipingpu concrete-faced rockfill dam, which was subjected to high-intensity seismic load during the 2008 Wenchuan earthquake, were conducted through a series of large-scale drained triaxial compression tests. A hyperbolic relation between the input plastic work and the degree of particle breakage was found for Zipingpu gravel, independent of the initial void ratio and confining pressures. The stress-dilatancy for Zipingpu gravel was analyzed and compared with data from two rounded alluvial and three angular quarried gravelly and rockfill materials in the literature. A nearly linear relationship between the dilatancy D p and the stress ratio η was found at medium-to-large stress ratios before the peak stress ratio. The slope of the stress-dilatancy line before peak had slight dependence on the void ratio and confining pressure of the gravel. After peak, the stress-dilatancy relation shifts down compared with that before peak for the gravel specimen. The phase-transformation stress ratio decreased with increased confining pressure, with the exception of sub-rounded gravel with little particle breakage. A nearly linear relationship was found between the phase-transformation stress ratio M f and the state parameter ψ for the Zipingpu gravel, regardless of the void ratio and confining pressure of the specimens.

Undrained cyclic shear strength of crushable sands

Because of their lightweight and highly crushable and compressible nature, pumiceous sands are problematic from engineering and construction viewpoints. There has been very little information on their liquefaction characteristics, and most empirical procedures available in evaluating the liquefaction potential of sands are derived primarily from hard-grained sands. To understand the undrained cyclic behavior of pumice sands, several series of undrained cyclic triaxial tests were performed on two sets of pumice samples. One set of samples consisted of undisturbed pumiceous deposits taken from a site in Waikato, whereas the other set involved reconstituted pumice sands in both loose and dense states. The results obtained were compared with those observed in Toyoura sand, a typical (hard-grained) sand. The degree of particle breakage in pumice during cyclic shearing was examined, highlighting the effect of the crushable nature of the grains on the cyclic response of the soil.

Influence of Freeze-Thaw Action on Deformation-Strength Characteristics and Particle Crushability of Volcanic Coarse-Grained Soils

ABSTRACT The objective of this study is to evaluate the effect of freeze-thaw action on the deformation-strength characteristics of crushable volcanic coarse-grained soils, wherein significant particle breakage occurs even under relatively low stress levels and saturated conditions. A series of monotonic triaxial compression tests was performed for volcanic coarse-grained soils under various freeze-thaw histories. On the basis of the test results, we examined the above-mentioned effect and the relationship between the degree of particle breakage and the freeze-thaw history. The results indicate that the degree of particle breakage under consolidation and shear increased with freeze-thaw action; and consequently, the strength and the stiffness of the soils decreased with an increase in the number of freeze-thaw cycles. Moreover, to examine the influence of freeze-thaw action on the single-particle hardness of volcanic coarse-grained soils, single-particle crushing tests were conducted. The test results revealed that volcanic soil particles become more fragile after being exposed to freeze-thaw action, and as a result, the degree of particle breakage increases. These results indicate that the freeze-thaw action has a strong influence on the deformation-strength characteristics of crushable volcanic soils in terms of an increase in particle breakage, even if the soils lack frost-heave characteristics.

Particle Breakage of Gypsum Granular Materials in Triaxial Compression Tests

In order to study the particle breakage of granular materials during compression, a series of triaxial compression tests were conducted for gypsum granular materials. Meanwhile, the primary study on evolution laws of particle breakage was carried out. It was found that the deviator stress increases with the increase in confining pressures for gypsum granular materials at the same axial strain. The degree of particle breakage of gypsum granular materials increases with the increase in confining pressures. The relative breakage index can be adopted to denote the particle breakage degree and increases with the increase in confining pressures. When the initial grain size distribution of gypsum granular materials is fractal, the grain size distribution complies with fractal during compression under different confining pressures. The fractal dimension increases with the increase in confining pressures and can be adopted as a parameter for measuring the degree of particle breakage.