Granular Matter最新文献

Most previous studies have focused on the small-strain shear modulus (G_max) of clean sand or sand-silt/clay mixtures, while little attention has been given to sand-gravel mixtures which are extensively used in many construction projects, such as railway foundation, rockfill dam and artificial slope. This study investigates the effect of gravel content (GC) on the G_max through a series of shear wave velocity tests on specimens with 0 to 100% GC in a large-scale triaxial apparatus. The results show that the relationship between G_max and GC is related to the stress level. Under relatively low confining pressure, the G_max remains nearly constant when GC increases from 0 to 80%, after which, G_max increases rapidly until 100% GC. Under relatively high confining pressure, the G_max increases slowly when GC increases from 0 to 40%, the rate of increase in G_max becomes more rapid at 40–80% GC, and the G_max increases most rapidly between 80 to 100% GC. The observed difference in the relationship between G_max and GC is related to the stronger densification for specimens with between 40 and 80% GC at higher confining pressure. A G_max model considering the effect of GC was established and verified using the test data. The model can assist with rapid estimation of the small-strain shear modulus of sand-gravel mixtures.

This article presents a theoretical prediction of elasto-plastic collision during normal impact. A new theoretical model is proposed to estimate coefficient of restitution and contact force–displacement characteristics during elasto-plastic collision. The proposed model can be considered as a modified version of Thornton’s model which comes into a very good agreement with FEA and experimental works. This model takes care of non-local plasticity as well as uniform pressure distribution instead of constant pressure distribution in core contact region in plastic phase. Concept of contact ring is proposed for first time in this article. The effect of adhesion on the proposed contact model is also discussed in this article. The validity of proposed contact model for a wide range of impact velocity proofs the model to be robust.

The response of a granular alignment held between fixed end walls to an impulse was introduced in the works of Nesterenko between 1983 and the years that followed. He showed analytically and experimentally that a granular chain admits a propagating solitary wave. In his analytic work, under small precompression compared to the local strain, he showed that one finds a propagating solitary wave. The solitary wave was also seen experimentally but at zero and vanishingly small precompressions. Under stronger precompression a possible Korteweg–de Vries (KdV) solitary wave was suggested though never observed. Later, others confirmed the solitary wave result at zero loading. Sen and Manciu reported seeing the solitary wave behavior in numerical simulations and in 2001 proposed an accurate solution which obtained the solitary wave at zero precompression as seen in some experiments and in numerics. Simulations showed an oscillatory tail following the solitary wave at small precompressions. In an experimental study in 1997, Costé, Falcon and Fauve and later Nesterenko et al. reported seeing propagation of a wave with an oscillatory tail. The oscillatory tail eventually consumed the solitary wave with increasing precompression. How can one reconcile Nesterenko’s solitary wave for the weakly precompressed system with Sen and Manciu’s solitary wave solution for zero precompression? Here we show that there is a separate solitary wave phase at a certain weak but finite loading regime which is distinct from Sen and Manciu’s work and this may be the reason why Nesterenko’s analytic theory seems to admit a solitary wave at finite loadings. We also offer insights into why the KdV solution is not seen.

This paper presents an erosion interpretation of cohesive granular materials stressed by an impinging jet based on the results of a micromechanical simulation model. The numerical techniques are briefly described, relying on a two-dimensional Lattice Boltzmann Method coupled with a Discrete Element Methods including a simple model of solid intergranular cohesion. These are then used to perform a parametric study of a planar jet in the laminar regime impinging the surface of granular samples with different degrees of cohesive strength. The results show the pertinence of using a generalized form of the Shields criterion for the quantification of the erosion threshold, which is valid for cohesionless samples, through empirical calibration, and also for cohesive ones. Furthermore, the scouring kinetics are analysed here from the perspective of a self-similar expansion of the eroded crater leading to the identification of a characteristic erosion time and the quantification of the classical erosion coefficient. However, the presented results also challenge the postulate of a local erosion law including erodibility parameters as intrinsic material properties. The paper then reviews the main limitations of the simulation and current interpretation models, and discusses the potential causes for the observed discrepancies, questioning the pertinence of using time-averaged macroscopic relations to correctly describe soil erosion. The paper concludes addressing this question with a complementary study of the presented simulations re-assessed at the particle-scale. The resulting local critical shear stress of single grains reveals a very wide dispersion of the data but nevertheless appears to confirm the general macroscopic trend derived for the cohesionless samples, while the introduction of cohesion implies a significant but systematic quantitative deviation between the microscopic and macroscopic estimates. Nevertheless, the micro data still shows consistently that the critical shear stress does actually vary approximately in linear proportion of the adhesive force.

Rotary drums equipped with longitudinal flights are mainly used to dry granular solids and handle high throughputs. The design of the flights is a crucial task because they decisively influence the distribution of the particles over the dryer cross section. In a previous work, the authors derived a mathematical model for the particle flow in rotary drums with rectangular flights. In this model, the final discharge angle was underpredicted resulting in errors when calculating the contact area of the particles in the air-borne phase. Therefore, a new model was developed in this study to predict the final discharge angle based on a forces balance approach on a single particle. This approach includes the Coriolis force acting on the last discharging particles sliding down the inclined flight sheet. The model was solved by using the vector analysis method. Experiments were performed at rotary drums with 0.5 m and 1.0 m in diameter, respectively, and 0.15/0.3 m in length using glass beads and quartz sand as bed materials. Each drum was equipped with 12 flights around the shell. The model validation was performed by varying the bed material, drum diameter, flight length ratio, and the rotating speed. The model predictions have shown that as the flight length ratio and the Froude number increased, the final discharge angle attained higher values. The model predictions agree well with the measurements.

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The filling characteristics of rockfill is an engineering problem that cannot be ignored in high dams. Reasonably controlling and optimizing the gradation is critical for improving the compaction quality. The relationship between gradation distribution law and compaction characteristics is investigated using numerical and field experiments, and a method for dam construction gradation design optimization is given. The results show that the Weibull model exhibited better applicability for continuous coarse-grained soil gradation. The extreme porosity of rockfill has a scaling effect, which can be basically eliminated when the maximum particle size reaches 400 mm. The prediction results based on the neural network show that the Weibull model gradation parameters strongly correlate with the porosity. The “occupancy effect”, or “filling effect”, of fine particles, and the “wedge effect”, or “wall effect”, of coarse particles, can explain the relationship between the Weibull model gradation parameters and porosity. The gradation parameters have a corresponding relationship with the classical non-uniformity coefficient Cu and curvature coefficient Cc indexes. Cu and Cc indicators can be used to judge the quality of the gradation at first and then optimize it by using the experimental results of the Weibull model parameters. The research results have application reference value for the filling design and compaction quality evaluation of large-scale coarse-grained soil.

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