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Scale effects of shallow foundation bearing capacity on granular materials were investigated to further evaluate the trend of decreasing bearing capacity factor, [N.sub.[gamma]], with increasing footing width, B, observed by other researchers. Model-scale square and circular footing tests ranging in width from 0.025 to 0.914 m were performed on two compacted sands at three relative densities. Results of the model-scale footing tests show that the bearing capacity factor, [N.sub.[gamma]], is dependent on the absolute width of the footing for both square and circular footings. Although this phenomenon is well known, the current study used a large range of footing sizes tested on well-graded sands to show that the previously reported modifications to the bearing capacity factor, [N.sub.[gamma]], using grain-size and reference footing width do not sufficiently account for the scale effect seen in the test results from this study. It also shows that behavior of most model-scale footing tests cannot be directly correlated to the behavior of full-scale tests because of differences in mean stresses experienced beneath footings of varying sizes. The relationship of the initial testing conditions (i.e., void ratio) of the sand beds and mean stress experienced beneath the footing (correlated to footing size) to the critical state line controls footing behavior and, therefore, model-scale tests must be performed at a lower density than a corresponding prototype footing in order to correctly predict behavior. Small footings were shown to have low mean stresses but high [N.sub.[gamma]] values, which indicates high operative friction angles and may be related to the curvature of the Mohr--Coulomb failure envelope. DOI: 10.1061/(ASCE)1090-0241(2007)133:10(1192) CE Database subject headings: Shallow foundations; Bearing capacity; Scale effects; Sand; Granular materials.

A constitutive model has been developed to capture the behavior of cross-anisotropic frictional materials. The elastoplastic, single hardening model for isotropic materials serves as the basic framework. Based on the experimental results of cross-anisotropic sands in isotropic compression tests, the principal stress coordinate system is rotated such that the model operates isotropically within the rotated framework. Experimental plastic work contours on the octahedral plane are plotted for a series of true triaxial tests on dense Santa Monica Beach sand to study the effects of cross anisotropy on the evolution of yield surfaces. The amount of rotation of the yield and plastic potential surfaces decreases to zero (isotropic state) with loading. The model is constructed for cases where the principal stress and material symmetry axes are collinear and no significant rotation of principal stresses occur. The model incorporates fourteen parameters that can be determined from simple experiments, such as isotropic compression, drained triaxial compression, and triaxial extension tests. A series of true triaxial and isotropic compression tests on dense Santa Monica Beach sand are used as a basis for verification of the capabilities of the proposed model. CE Database subject headings: Granular materials; Anisotropy; Isotropic materials; Compression tests; Triaxial tests; Models.

This paper focuses on the mechanisms occurring in a granular earth platform over soft ground improved by rigid piles. Two-dimensional physical model experiments were performed using the Schneebeli's analogical soil to investigate the load transfer mechanisms by arching and the settlement reduction and homogenization. Experimental outputs are compared to results obtained on a numerical model using a plane strain continuum approach. The impact of the constitutive model complexity to simulate the platform material behavior was first assessed, but no large difference was recorded. As lar as the proposed model, which takes the main features of the observed behavior satisfactorily into account, the numerical procedure could be validated and the parametric studies extended numerically. Both approaches of this study underlined the main geometrical and geotechnical parameters which should inevitably be taken into account in a simplified design method, namely the capping ratio, the platform height, and the platform material shear strength. DOI: 10.1061/(ASCE)1090-0241(2007)133:3(295) CE Database subject headings: Piles; Soil stabilization; Granular materials; Numerical models; Scale models; Two-dimensional models: Soft soils.

This paper presents a sensitivity analysis of the input parameters of a program based on the discrete element method (DEM). Triaxial compression simulations were conducted on an assembly of ellipsoids with two particle shapes. We examine four input parameters including shear modulus of particles, density of particles, time step, and damping. Generally, these parameters are chosen by calibrating the result with certain known behavior of granular materials. In dynamic simulations, these input parameters are bounded by their physical attributions that should not be altered. However, in static simulations, they do not have the same physical implication. Validity of results may be questionable when input parameters are used without justification. A sensitivity analysis of the input parameters should shed light on this issue. In this paper, we will study the effect of the input values within the range of (1/10)-10 times the benchmark value. The benchmark values are commonly used by the writer. The results are presented against the benchmark simulation. The unbalanced forces in the simulations are kept below a prescribed value to enforce equilibrium. The result shows that the effect of all input parameters used in this paper is negligible as long as the small unbalanced forces in the system can be achieved. The runtimes are different. However, there are two simulations (one with low damping and the other with a large time step size) that cannot maintain the required small unbalanced force. In other words, equilibrium cannot be achieved for these simulations. CE Database subject headings: Granular materials; Discrete elements; Triaxial Compression; Micromechanics

A new numerical code based on the Distinct Element Method (DEM) is developed to study the impact cratering processes on granular material. This code has a potential advantage to simulate the cratering process on granular material, since the movement of discrete particles can be treated. To show the physical plausibility of this code, we conduct 3-D numerical simulations of vertical impact into granular material targets that consist of 384,000 particles, and compare the results with those from experimental studies. It is shown that the excavation stage of cratering derived from experimental studies is represented well by our simulation: the size of the crater cavity, and the ejecta velocity and angle distributions are consistent with those obtained in laboratory experiments. The impact simulation code developed in this study is thus suggested to be useful for the analysis of the impact cratering process on granular material. Keywords: Cratering; Impact processes; Computer techniques

Repeated load triaxial tests are widely used to determine nonlinear behavior of unbound granular materials. However, conventional triaxial specimen preparation techniques may not be able to reconstruct the internal structure of a material which has great impact on some of the nonlinear parameters. In addition, it is difficult to reproduce in situ stress conditions in a triaxial cell. In this study, full-scale cyclic and static laboratory plate load tests were performed to investigate the mechanical properties of unbound granular materials. An algorithm was developed to backcalculate nonlinear parameters for prediction of models as a function of bulk stress. Study results demonstrate the pronounced influence of water content on the behavior of unbound granular materials and a generally linear relation between nonlinear parameter [K.sub.1] and the degree of saturation. CE Database subject headings: Granular materials; Base course; Flexible pavements; Bearing capacity; Nonlinear analysis; Parameters.

A densely packed granular system is an example of an out-of-equilibrium system in the jammed state. It has been a longstanding problem to determine whether this class of systems can be described by concepts arising from equilibrium statistical mechanics, such as an effective temperature and compactivity. The measurement of the effective temperature is realized in the laboratory by slowly shearing a closely packed ensemble of spherical beads confined by an external pressure in a Couette geometry. All of the probe particles considered in this study, independent of their characteristic features, equilibrate at the same temperature, given by the packing density of the system. granular matter | jamming | statistical mechanics of grains

Rotation of particles in granular material is an important mechanism, which is responsible for the distinct feature of moment transfer within granular material. A couple-stress continuum is adopted to model such effect. The paper presents a mix-mode finite element formulation for the analysis of a couple stress continuum. A modified variational formulation is proposed to render unconditional convergence. The developed finite element method is validated by comparing the computed results with closed-form solutions. In order to verify whether the couple-stress continuum is appropriate for modeling granular media, finite element results for two different boundary value problems are performed and compared with that obtained from discrete analysis. Physical meaning of internal length, a new parameter of the material, is discussed. The suitability of the couple-stress continuum for modeling granular medium is evaluated. CE Database subject headings: Granular materials; finite element method; Bonding; Elastic analysis; Deformation analysis; Stress distribution; Numerical models; Two-dimensional analysis.

One of the important components of a flexible pavement structure is granular material layers. Unsaturated granular pavement materials (UGPMs) in these layers influence stresses and strains throughout the pavement structure, and have a large effect on asphalt concrete fatigue and pavement rutting (two of the primary failure mechanisms for flexible pavements). The behavior of UGPMs is dependent on water content, but this effect has been traditionally difficult to quantify using either empirical or mechanistic methods. This paper presents a practical mechanistic framework for determining the behavior of UGPMs within the range of water contents, densities, and stress states likely to be encountered under field conditions. Both soil suction and generated pore pressures are determined and compared to confinement under typical field loading conditions. The framework utilizes a simple soil suction model that has three density-independent parameters, and can be determined using conventional triaxial equipment that is available in many pavement engineering laboratories. DOI: 10.1061/(ASCE)1090-0241(2004)130:9(896) CE Database subject headings: Unsaturated soils; Granular materials; Pavements; Soil suction.

This paper presents the use of x-ray tomography imaging to reconstruct a three-dimensional (3D) digital representation of individual particles in a granular system. The granular system is represented by the mass center coordinates and the morphology representation of each particle. An automated procedure using pattern recognition to identify related particle cross sections in adjacent serial images was developed. Procedures to calculate quantities needed for subsequent simulation of particle behavior including the volume and the momentum of inertia of each particle are also presented. The developments described in the paper enable modeling and simulation of the behavior, and experimental observations of the particle kinematics of real microstructures of granular materials in a true 3D platform. CE Database subject headings: Microstructure; Granular materials; Morphology; X-ray analysis; Radiography; Particles; Digital techniques.

A new approach for making face-centered tetragonal FePt nanoparticles with a diameter of 17 nm and granular films from Pt@Fe2O3 core-shell nanoparticle precursors is described. The core-shell nanoparticles are converted to fct FePt through a reduction and alloy formation process at enhanced temperatures.

Granular materials exhibit a complex variety of fluid and solid collective regimes which has led researchers to consider them as a new state of matter all on us own. In this paper we investigate the behaviour of granular materials by means of Hurst rescaled range analysis. We analyse records in time of the angle of the slope of granular materials partially filling a rotating drum and records of the local backscattered light from fluidized beds. We show that the Hurst analysis is able to identify phase transitions as well as to characterize spatio-temporal structures. The influence of interparticle attractive interactions on the memory of granular materials is also investigated.

Microstructure and giant magnetoresistance of granular Au80Co20 were studied.

A variable time step Monte Carlo technique was used to model the effect of interactions on blocking temperature of granular magnetic films.

Hexagonal closed packed CoCrPt-C granular media was studied for magnetic and structural properties.

Granular films were prepared using dc magnetron co-sputtering.

Granular thin AgFe films were studied for magnetoresistance.

A series of biaxial (plane strain) experiments were conducted on three sands under low (15 kPa) and high (100 kPa) confining pressure conditions to investigate the effects of specimen density, confining pressure, and sand grain size and shape on the constitutive and stability behavior of granular materials. The three sands used in the experiments were fine-, medium-, and coarse-grained uniform silica sands with rounded, subangular, and angular grains, respectively. Specimen deformation was readily monitored and analyzed with the help of a grid pattern imprinted on the latex membrane. The overall stress-strain behavior is strongly dependent on the specimen density, confining pressure, sand grain texture, and the resulting failure mode(s). That became evident in different degrees of softening responses at various axial strains. The relationship between the constitutive behavior and the specimens' modes of instability is presented. The failure in all specimens was characterized by two distinct and opposite shear bands. It was found that the measured dilatancy angles increase as the sand grains' angularities and sizes increase. The measured shear band inclination angles are also presented and compared with classical Coulomb and Roscoe solutions.

The anomalous microwave response of Yba2Cu3O7-delta granular thin films under magnetic fields has been examined.

FE-Cu granular alloys were prepared using the Bridgeman method, and antiferromagnetic correlations were studied.

The behaviors observed in granular mixing are described.

Energy dissipation in sheared granular flows has been studied. A two-dimensional discrete element computer simulation of a bounded, gravity-free Couette flow of particles was used and the heat dissipation rate per unit area calculated as a function of position in the flow and overall solid fraction. Cooling rate is measured for binary mixtures of particles for varied small-to-large solid fraction ratios. The thermodynamic temperature and the cooling rate go up with size ratio and with decreasing ratio of small to large particles in mixtures.

Research was conducted to examine the magnetic properties and structure of a series of granular Fe(sub 1-x)Co(sub x)/SiO2 and Ni(sub 1-x)Co(sub x)/SiO2 films. The thermal relaxation theory successfully explains the experimental results by assuming the surface anisotropy dominates in the giant magnetic coercivity effect. The surface anisotropy concept based on Neel's theory demonstrates that qualitative similarity to the fitting results as a function of Co contents.

A study on the use of granular magnetic thin films as ultra-high density recording media was conducted to investigate magnetic interactions in very thin Fe-SiO2 films. The experiment constructed delta m plots for granular thin films. Measurements of the activation volume for the thinnest films suggest 2D interactions rather than 3D interactions which are associated with very low values of the magnetic viscosity. Experimental methods and results are presented.

In discrete numerical modeling of granular materials, idealization of individual particles is required, as it is not practical to model a large number of particles, each with its actual shape and size. To minimize computation times, researchers often use two-dimensional, circular elements. However, biaxial and direct shear tests on such specimens result in low strengths compared to granular materials, due, in part, to excessive rolling of the perfectly circular particles. In this paper, a new particle type, disk clusters, is presented. A disk cluster is a group of circular disks permanently connected to form an irregularly shaped particle that more closely represents the shape of granular materials and has less tendency to rotate. Development and implementation of disk cluster particles into a discontinuous deformation analysis program is presented. Validations of the mechanics of a single disk cluster, biaxial shear, and anchor pullout simulations illustrate the usefulness of this new particle type.

Experimental mixing patterns in small tumblers partly filled with fine glass beads were produced. Numerical results were generated from a periodically forced continuum model. The grains were identical in both experiment and model, apart from colour. A periodic stick-slip behaviour occured in the shear layer separating static and flowing regions, causing the beads to mix at rates exceeding those previously achieved.

Volume scattering and absorption of electromagnetic radiation by a nonmagnetic, granular medium with large dielectric contrast has been achieved using an improved Born approximation. The low-frequency model is used to derive formulas and measured dielectric properties are used to obtain relevant model data of dry snow. The results reproduce Rayleigh scattering for a single particle.

Using a rotating HGMS ordered matrix in a quasi-transversal configuration, experiments have been performed to study the dependence of the captured mass [m.sub.s] on the angle [Alpha] between the direction of the applied field [H.sub.o] and the ferromagnetic wires. The ordered dependence of [m.sub.s] on [Alpha] registered experimentally reveals the possibility to successively separate a granular mixture by an adequate choice of the inclination angles (angular steps) without modifying the applied field [H.sub.o] or the average flow velocity [v.sub.a]. Relationships were derived connecting the magnetic susceptibilities of the mixture components with the inclination angle [Alpha] in order to accomplish such a separation in angular steps. Index Terms - Angular steps, granular mixture, magnetic separation, magnetic susceptibility.

In the sheetflow regime, the concentration of the sediment is so high that particle/particle interaction plays an important role. In this study, a numerical simulation of the sediment transport in the sheetflow regime is performed on the basis of the Distinct Element Method (DEM) with a focus on particle/particle interaction. The characteristics of the vertical velocity profile of sediment particles in the sheetflow regime, which were reported in previous experiments, are reproduced well by the present simulation. Furthermore, the mechanism to determine the velocity profile of the sediment particles is clarified from the viewpoint of the granular material dynamics. Finally, the half-cycle averaged sediment transport rate under an action of sinusoidal oscillating flow is estimated from the result of the simulation under the quasi-steady assumption and is compared with the result of previous experiments.

An experiment was conducted to study the effects of annealing on the structural, magnetic and magnetotransport properties of melt-spun Co10Cu90 granular alloys. The interaction effects were studied from both remanent magnetization and magnetotransport data, using two different methods to reach the demagnetized state, ac and dc demagnetization. Results show the role of some structural parameters and the degree of magnetic correlation in the magnetic field response of the resistance in these inhomogeneous systems.

A study was undertaken to determine the drainability characteristics of several types of unbound granular materials that are used in pavement bases. From the literature, testing concerns were identified and analyzed. Hydraulic conductivity and effective porosity were determined for aggregates from two sources of crashed stone and two sources of gravel. For each material two open gradations were tested in a rigid wall permeameter. One dense gradation of each material, at two levels of compaction, was tested in a flexible wall permeameter as well. Efforts were made to reduce possible flow along the sides of the rigid wall permeameter and to eliminate problems with air bubbles. The average hydraulic conductivities for the open and dense-graded materials were 3.6 x [10.sup.-1] and 3.0 x [10.sup.-4] cm/s (1,021 and 0.85 ft/d), respectively. The effective porosities for the open and dense-graded materials were 68 and 27% of the nominal porosities, respectively. Four regression equations representing a wide range of hydraulic conductivity were developed to estimate hydraulic conductivity based on the results of this study and others reported in the literature.

A study was conducted on the confining pressure-caused crushing of granular particles. Results show that particle crushing is reduced by enhancing mineral hardness and that smaller amounts of breakage for a given stress is achieved with stronger or harder particles. Results are consistent with those obtained from the crushing of sedimentary rock-derived oversized particles.

Radio frequency sputtering at different sputtering conditions was conducted to develop Co-Ag granular films with various Co grain sizes. The grain sizes were determined through the division of magnetization curves into superparamagnetic and ferromagnetic components. The magnetoresistance was found to be proportional to the superparamagnetic grains' volume density. The giant magnetoresistance is attributed to spin-dependent scattering of the grain surfaces and inner parts.

A study developed a simple theory of macroscopic elasticity of granular systems based on several models of the grain-grain contact forces which are related to the fundamental Hertz theory. The study considered only the special cases of perfect friction or no tangential friction. The result showed that the energy is well defined for all values of the macroscopic strain when the tangential contact stiffness is independent of the normal force.

The giant magnetoresistive (GMR) properties of as-deposited and aged Fe-XCr-Co thin ternary alloy films were investigated as a function of the aging conditions and chromium content. The results, which showed a correlation between the MR values and the heterogeneous microstructure, indicated that the magnitude of the GMR depends on the grain size and density of the iron-chromium-rich precipitate.

The physics of granular materials is governed by Newtonian and hydrodynamic principles. Forces exist between the granules which affect the materials' kinetic behavior. This theorem can be used to explain a wide range of astrophysical phenomena.

The vertical vibrations in a bed of granular material cause at least one sudden bed expansion for a critical acceleration amplitude. A bifurcation in bed dynamics, having an effective coefficient of restitution greater than zero, causes the sudden expansion in the case of shallow beds. Deeper beds show heaping when the coefficient is equal to zero and exhibit a period doubling bifurcation instead of the sudden expansion. Results of a study using beads are compared with a model based on a ball bouncing on a vibrating plate.

Laboratory studies on small-size samples have revealed that the liquefaction potential of sand deposits can be significantly reduced by the reinforced earth technique. About 150 tests were performed on 38-mm diameter samples with woven geotextile, nonwoven geotextile, and coif as reinforcement to study the liquefaction behavior of reinforced soil. This paper evaluates the liquefaction potential of reinforced sand under triaxial stress conditions. A simple analytical method for soil liquefaction based on the cyclic triaxial tests conducted on reinforced sand is presented. The restraining effect of the reinforcement is accounted for as an additional confining stress. Good agreement between the analytical and experimental values is noticed. The results show that the bending stiffness and compressibility of the reinforcement played a dominant role in the shear mobilization along the soil fabric interface. The writers also performed tests on larger-diameter samples and the results revealed that the size effect is marginal, with the results falling on the conservative side.

An experimental study on granular materials in triaxial extension at confining pressures from 0.25 to 68 MPa is presented. Drained and undrained tests were performed utilizing cylindrical specimens. Strain localization was repeatedly encountered in the form of specimen necking. The strain localization was determined to initiate very early in the test. The cause of the strain localization was determined to be the inherent instability in the axisymmetric extension test, which allows stresses, and therefore deformations, to concentrate at the weakest part of the specimen. This instability is a result of the inward radial strains experienced during the extension test. The effect is to lower the measured failure stresses and strains resulting in the conclusion that the conventional extension test is unreliable for determining soil strength in extension. A method was developed to enforce uniform strains in triaxial extension tests on cylindrical specimens by the use of small metal plates separated by lubricated latex membranes. Using this method a series of uniform-strain tests were performed. Detailed comparisons between strain-localized and uniform-strain tests are presented.

The critical current density of a granular superconductor was examined as a function of temperature and magnetic field within the framework of a network of Josephson junctions (JJ) and inductances. Two JJ models were considered: tunnel junctions and weak links. The analysis showed that the overall behavior of the critical current density differs significantly from that of the bias current for a single junction.

Comparisons of physical experiments with computer simulations of collision-dominated granular flows in channels slightly wider than the particle diameters indicate that drag effects play a major role in flows of small particles in air or more viscous fluids. Flow chute geometry also has a significant effect on flow characteristics, but particle interaction effects are relatively insignificant.

Essential to the development of rate-type, elastoplastic constitutive models to describe the stress-strain behavior of any soil is knowledge concerning magnitude and direction of plastic strain upon application of an incremental stress. A series of stress-probe experiments are performed on a granular material with the objective of developing some understanding of these aspects. Triaxial sand specimens, loaded initially to different specified states of stress, are subjected to incremental stress probing in different directions, and the corresponding strain responses are measured. The results indicate that while the behavior approximately conforms to the theory of plasticity for stress states close to the failure line, it deviates from it for stress states close to the isotropic axis.