Wall Friction Angle Research Articles

Rigorous lower and upper bounds for the 3D passive earth pressure problem

With the advent of advanced numerical methods, the three-dimensional (3D) passive earth pressure problem has received increasing attention within the last two decades. However, narrow brackets for the exact solution obtained via lower and upper bound simulations have not been presented. In this study, finite-element limit analysis is utilised to determine rigorous bounds for the 3D passive earth pressure problem. A parametric study accounting for different wall geometries, friction angles and wall friction ratios is performed and results are presented in terms of lateral earth pressure coefficient, Kpγh. The results of the lower and upper bound analyses show that in all analysed cases, the exact solution is bracketed within a very narrow range. Furthermore, comparison with existing approaches reveals that, in general, a good agreement is achieved between the current results with data from literature. Furthermore, both lower and upper bound have been improved, especially for narrow geometries, large friction angles and large wall friction ratios.

Roller Compaction Scale-Up Made Simple: An Approximate Analytical Solution to Johanson's Rolling Theory

An approximate analytical solution to Johanson's rolling theory is derived. It is shown that the solution yields a single dimensionless parameter invariant in process scale-up or equipment transfer, which relates the densification factor with process parameters (roll force and gap), geometric parameters (roll diameter and width) and material properties. It is shown that, to a first approximation, the model prediction does not depend on the nip angle evading the need to powder rheometry measurements such as wall friction and internal shear angle. The model is benchmarked against data obtained from pilot-scale roller compactors from different manufacturers as well as literature data from Nesarikar. The model yields good ribbon density predictions even when calibrating material properties from uniaxial die compression.

Effect of the cleaning process on physical properties for different malting barley seed varieties.

The aim of the study was to investigate the influence of the barley cleaning process in relation to physical properties. The knowledge of the range of changes in the physical parameters of processed material and their mutual relationships is required for the design and implementation of various technological processes. In this study were compared the input and output commodities in the primary postharvest cleaning process of undesirable components—occurring as admixtures of fine and coarse barley impurities as well as the barley component itself. An efficient cleaning process ensuring barley grain quality is a basic step in beer production. Therefore, seven bred varieties of brewing barley (Malz, Sebastian, Francin, KWS Irina1, KWS Irina2, Bojos, and Laudis) were tested for the qualitative assessment of the cleaning process. Physical parameters such as granulometry, bulk and tapped density, angle of repose, internal and wall friction angle, and flow functions were determined for all samples. In order to identify whether the barley variety or the sample cleaning significantly influences the determined physical properties, two‐way ANOVA was applied. The results imply that barley cleaning had the main influence on wall friction angle, while the barley variety had a significant effect on effective internal friction. Moreover, the mechanical postharvest cleaning process reduces the overall wall friction.

Physical and flow properties of pseudocereal-based protein-rich ingredient powders

Knowledge of bulk handling properties of food powders is essential in the design of industrial equipment and selection of appropriate powder handling operations. The objectives of this study were to determine the physical and flow properties of plant-based regular and protein-rich flours to establish relationships between powder physical and bulk handling properties as influenced by protein enrichment. A number of physical properties (bulk density, flowability, wall friction and compressibility) were assessed for 11 regular- and protein-rich flours from pseudocereals (amaranth, buckwheat, quinoa) and cereals (rice and maize). Relevant physicochemical properties such as particle size distribution, microstructure and water sorption behaviour were also studied. The protein-rich pseudocereal flours had irregular-shaped, rough surfaces with mean particle diameters ranging from 96.5 to 215 μm. The compressibility indices (42.6–51.4%) were higher for the former compared to the regular protein content powders and they displayed lesser tendency to uptake water with increasing relative humidity. Analysis of the flow behaviour showed the protein-rich flours to be more cohesive with higher wall friction angle values than the regular protein content powders. The new information obtained in this study is critical in optimising the processing, stability and applications of these value-added high-protein pseudocereal ingredient powders.

Effect of Soil–Wall Friction Angle on Behaviour of Sheet Pile Wall Under Surcharge Loading

In this study, a solution is derived in the framework of the limit equilibrium approach for the design of cantilever sheet pile walls under both static and seismic conditions in cohesionless soil with uniform surcharge load located at the top of the wall. The proposed method satisfies the horizontal force equilibrium and moment equilibrium about toe simultaneously. From the results of the study, it is highlighted that the application of surcharge load increases the magnitude of bending moment along the depth of the sheet pile wall and deflection at the top of the wall. Further, the increase in plastic zone due to mobilisation of earth pressure is also observed. A parametric study is done by varying the soil–wall friction angle and magnitude of uniform surcharge load acting on the backfill of the cantilever sheet pile walls. From the results, it is observed that as the soil–wall friction angle increases, the maximum bending moment, deflection, depth of plastic zone and settlement adjacent to sheet pile wall decrease. Further, the increase in the magnitude of uniform surcharge increases the maximum bending moment, deflection, depth of plastic zone and settlement adjacent to sheet pile wall.

Flow behavior of cocoa pulp powder containing maltodextrin

Abstract This study aimed to evaluate the influence of maltodextrin addition on the flow properties of cocoa pulp powder obtained by spray and freeze drying. Cocoa pulp samples received 15% and 30% (m m-1) maltodextrin DE20. Two drying methods were used, spray and freeze drying. Powder morphology was evaluated through scanning electron microscopy (SEM). Wall friction angle, bulk density and tapped density were determined. Carr index (CI), Hausner ratio (HR) and flow index (FI) were used to evaluate powder flow. The particles powders obtained by spray drying showed rounded shapes, whereas the freeze dried powder showed irregular shapes. Increased maltodextrin concentration in the samples altered the powder particle size by spray drying and powder particle surface by freeze drying. The powder by spray drying of the sample with 30% of maltodextrin showed smallest wall friction angles, 13.4 to 14.9. The powder by freeze drying of the samples with 15% and 30% of maltodextrin showed wall friction angles between 14.0 and 20.6. Regarding flow, the powders by spray drying containing 30% of maltodextrin showed the best CI, HR and FI, 24.88, 1.33 and 4.88, respectively, being considered an acceptable flow. According to CI, HR and FI values, samples with 15% of maltodextrin produced powder classified as difficult flow in both methods applied. The higher maltodextrin concentration in cocoa pulp, the lower agglomeration in the powder by spray drying and the smoother particles surfaces in the powder by freeze drying. The addition of maltodextrin to the samples, for both drying methods, improve the powder flow and decrease the powder cohesion.

Maltodextrin on the flow properties of green coconut (Cocos nucifera L.) pulp powder

ABSTRACT The study of the flow properties and particle surfaces of a food powder is essential for predicting its behaviour during processing and commercialization. The objective of this work was to determine the powder flow properties of lyophilized green coconut pulp with different concentrations of maltodextrin. Samples containing 0, 5, 10 and 15% (m/m) maltodextrin were lyophilized, and the flow index (FI), wall friction angles and densities were determined. The microstructure of the powders was evaluated by scanning electron microscopy (SEM). The samples containing 0 and 5% maltodextrin showed 1.87 FI, classifying them as very cohesive powders, and those containing 10 and 15% cohesive powder showed 2.12 and 2.43 FI, respectively. The powder densities varied from 138.6 to 287.6 kg/m3, and the wall friction angle varied from 15.8 to 39.8°. The powder particles presented irregular shapes and rough surfaces, especially in powders containing 0, 5 and 10% maltodextrin. The powder containing 15% had smoother and less agglomerated surfaces. An increase in the amount of maltodextrin added to the pulp made the particles smoother and denser and improved the fluidity of the powder.

Apparent density of compressible food powders under storage conditions

The stress-dependence of the apparent density and the wall friction angle of various food powders like salt, sugar, flour, starch and protein powders were studied using a ring shear tester. The approximation of the stress-dependence of the apparent density using a power function showed a very good correlation (r2 > 0.97). The two parameters of the approximation function are the apparent density at 1.0 kPa and the exponent, which characterizes the compressibility of the powder. The first correlates very well with the apparent density measured according to ISO 697 or EN ISO 60 (r2 = 0.98), while the second shows some correlation (r2 = 0.76) with the particle size. Combining the powder properties apparent density, the mass median diameter and the spread of the particle size distribution in a power function allows a reasonably good estimate of the exponent (r2 = 0.93). The wall friction angle usually decreases at higher values of the wall normal stress. This dependence can often be approximated using a simple function. However, for powders with a low stress-dependence of the wall friction angle it is better to use a constant average value. Thus, the apparent density of compressible food powders under storage conditions can be described well.

Pseudo-Static Limit Equilibrium Method for Bearing Capacity of Footing on Slope and Seismic Uplift Capacity of Horizontal Strip Anchor

Seismic bearing capacity for a shallow strip footing embedded in a sloping ground is derived along with seismic uplift capacity of horizontal strip anchors. c-ϕ soil medium is used with limit equilibrium method of analysis. A planar failure mechanism has been adopted. The seismic bearing capacity is determined in the form of a single pseudo-static bearing capacity coefficient (N γe ) in association with unit weight, surcharge and cohesion, which becomes more practical to simulate the actual field problem. The seismic forces are considered to act both on the footing and on the soil below the footing. The effects of soil friction angle, soil cohesion, wall friction angle, horizontal and vertical seismic accelerations are taken into account to evaluate the seismic bearing capacity of the foundation. Also seismic uplift capacity factors for horizontal strip anchors is found. The factor is determined as a function of embedment ratio, angle of internal friction of soil, angle of wall friction, cohesion of soil and seismic acceleration coefficients. The uplift capacity factors have been determined for the simultaneous resistance of cohesion and unit weight of soil. Effect of the vertical seismic acceleration coefficient has been found to always reduce the uplift capacity factor whereas the effect of horizontal seismic acceleration coefficient has also been found to reduce the uplift capacity factor in maximum cases. The results obtained from both the cases has been compared with existing literature and the effect of parametric variations discussed.

Spectral bearing capacity analysis of strip footings under pseudo-dynamic excitation

ABSTRACT Spectral seismic bearing capacity of strip foundations is evaluated by the limit equilibrium method (LEM). In this study, the pseudo-dynamic approach is followed to take into account seismic accelerations. The formulation of spectral pseudo-dynamic bearing capacity of strip foundations is presented for the Coulomb failure mechanism. The results are reported in the form of joint bearing capacity considering the contributions of cohesion, surcharge, and soil weight, simultaneously. A parametric study is conducted to evaluate the influence of soil friction angle, interface wall friction angle, dimensionless ratio of cohesion, depth factor, primary and shear wavelength values, amplification factor as well as the frequency on the seismic bearing capacity factor. The results of this study are shown in the form of design aids and tabular for the sake of simplicity to be used by engineers. The consistency of the results with those reported in literature shows the ability and efficiency of the methodology presented herein. It is shown that both the seismic loading characteristics and shear strength parameters affect the bearing capacity of shallow footings.

EFFECT OF SOME PROCESS VARIABLES ON THE STRENGTH, FLOWABILITY AND THERMAL PROPERTIES OF TIGERNUT (Cyperus Esculentus L) FLOUR

This work evaluated the effect of drying temperature, drying time and post sprouting sampling time (as theprocess variables) on flowability and thermal properties of tigernut flour. Response surface methodologywas employed in the experimental design. The flowability of the bulk solid tigernut flour was determined byapplying uniaxial compression test of granules using universal testing machine Instron 3369 and byapplication of the principle prescribed by Carvarlho et al., (2011) and Schulze (2011) and. thermalcharacteristics using thermal conducting probe and calibrated copper calorimeter. The result showed that thestrength of the tigernut flour at 2.01 and 3.02g/cm3 were higher than that at 1.62g/cm3 in all the studiedtigernut flour samples. The flow functions ranged from 4.01 to 4.86. tigernut flour sample from seeds tosprouted for 36 hours dried at 50oC for 12 hours had the lowest function while tigernut flour sample fromseeds sprouted for 43.53hours, dried of 56.44oC for 12.02 hours (optimized sample) had the highest flowfunction of 4.86. The friction angles which describe the flow properties of the tigernut flour ranged from41.50o to 42.20o for internal friction angle while the wall friction angles varied between 47.80 and 48.5, theangle of internal friction between the tigernut flour granules generally increased with an increase in bulkdensity in the range of 1.62 to 3.02 g/cm3, frictional factor and half hopper angle ranged from 1.51 to 1.52and 22.8 to 23o respectively. Angle of repose, Hausner ratio and Carr’s index ranged from 27.82 to 44.19;1.17 to 1.34 and 15.34 to 26.13 respectively, with easy flowability flour. Thermal conductivity, specific heatcapacity and diffusivity varied between 0.054 and 0.083Wm-1K-1; 390.73 and 1069.6 Jkg-1K-1; 1.197  10-4and 2.713  10-4m2s-1 respectively. This information could be useful in the industrial processing andhandling of tigernut flour.

Ground Settlement and Deflection Response of Cantilever Sheet Pile Wall Subjected to Surcharge Loading

Sheet pile walls are used to support moderate height of excavation. If bracing system or anchors are not provided, it gets stability mainly from passive earth resistance below the dredge line. Non-availability of large open space in metro cities gives the perception to engineers to go deeper in the earth and use sheet pile walls for supporting various types of works like parking space and housing utilities. To avoid the damage to surrounding structure, proper analysis of settlement and deflection of the wall should be carried out. The deflection and settlement of wall depend on soil properties, depth of excavation and wall properties. In the present study, cantilever sheet pile walls are analyzed under surcharge loading for settlement and deflection through pseudo-static approach using finite difference-based program FLAC2D. A parametric study is carried out assuming an elastic–perfectly plastic Mohr–Coulomb model with non-associated flow rule by varying the seismic coefficients, embedded depth, soil–wall friction angle, type of soil, magnitude of surcharge and distance from the top of the wall. The results show that by increasing the coefficient of horizontal seismic acceleration, the deflection and settlement of cantilever sheet pile walls increase. It is also observed that with an increase in distance of surcharge from top of the wall, both settlement and deflection decrease.

Predicting the critical outlet width of a hopper using a continuum finite element method model

In this work, the critical outlet widths (COWs) for continuous bulk solids flow predicted by Jenike's theory, the McLean correlation, Enstad's theory, and Finite Element Method (FEM) analysis are compared. The FEM predictions use a Mohr-Coulomb elasto-plastic constitutive model. Unlike Jenike's theory and the McLean correlation, Enstad's theory and the FEM model show that the COW depends on the material height. The effects of the material internal friction angle, slope of the flow function, wall friction angle, and hopper half angle on the COW predictions are explored. Comparisons to experimental COWs from the literature show that the FEM model provides, by far, the best predictions. The primary advantage of using an FEM model for COW predictions are that complex materials and hopper geometries may be simulated, where simplifying assumptions of the standard theoretical models are not valid.

New mass flow limiting lines based on segregation pattern and magnitude

Mass flow, by definition, means all of the mass in a hopper will move when some material is discharged from the outlet. Mass flow has been the recommended means to solve segregation issues. This generally works under conditions where the segregation pattern is radial and when the process operation is nearly steady state flow into and out of the hopper. If the segregation pattern is either axial or radial, but the mode of operation is to fill followed by completely emptying the bin, then segregation can easily be an issue – even in mass flow designs. Segregation prevention is all about velocity control, and matching the velocity to the segregation pattern and mode of operation.Ideally, one would like to estimate segregation using easily measured flow properties, segregation potential tests, and a description of the process geometry. This paper looks at a method of predicting segregation problems using flow properties like wall friction angle and effective internal friction angles coupled with the radial stress theory to compute the expected velocity profiles in a variety of process geometries. Using slope stability models, one can also relate the cascade behavior of cohesive material down a pile or slope. Imposing radial stress velocity profiles and cascade velocity profiles in a bin or hopper, then using particle tracking techniques, one can compute the time at which any particle in any portion of the bin might exit the system. Furthermore, imposing a measured segregation profile on the material initially placed in the bin, and then tracking groups of particles with an assigned segregation concentration through the bin, can help determine when and how segregated material might exit the bin. Doing enough of these calculations for a range of wall friction angles and hopper slope values, the velocity profile can be related to the segregation intensity exiting the bin as a function of these two variables. Since these two variables also determine the propensity for mass flow, this analysis can relate mass flow to segregation tendency for material subject to a filling and discharge mode of operation. Selection of an optimal mass flow design would then depend on the segregation pattern and the desired segregation intensity the process can live with.Applying this methodology to a conical hopper suggests that a material prone to segregation will segregate significantly in a funnel flow design. This is to be expected. However, this work also indicates that mass flow bins, when filled and then emptied completely, may experience significant segregation if the hopper walls are designed with traditional mass flow limits in mind. This work suggests that mass flow hoppers must be considerably steeper to mitigate segregation effects for a fill-then-empty mode of operation.

Effects of Mobilized Wall Friction Angle on Resultant Seismic Earth Pressure on Shallow Foundation

AbstractTo investigate the seismic earth pressure on a shallow foundation, a dynamic centrifuge test using a sinusoidal sweep motion was performed on a superstructure–footing model embedded in dry ...

Microstructure and flow properties of lyophilized mango pulp with maltodextrin

ABSTRACT The present study had as objective to determine the flow properties and behavior of lyophilized mango pulp powder as a function of different concentrations of maltodextrin. In the samples of the powders contain 5, 10 and 15% of maltodextrin the angle of effective internal friction, wall friction angle, flow index and bulk density were determined. The microstructure was evaluated by scanning electron microscopy. The freeze-dried samples are characterized as having an amorphous structure, and the drying aid used modified the surface of the particles. The flow index was 3.19, 4.28 and 4.53 for samples containing, respectively, 5, 10 and 15% maltodextrin. Increasing the concentration of maltodextrin in the mango pulp decreased the effective angles of internal friction and wall friction. The bulk density of the powders increased with increasing concentration of maltodextrin for the samples containing 5, 10 and 15% of the maltodextrin, being equal to 597.8, 689.8 and 691.3 kg m-3, respectively. Thus, it was concluded that the addition of maltodextrin modified the shape of the particles, decreased segregation, affected the flow properties of the mango powders, facilitating flow and increasing their bulk density.

Computation of sliding displacements of seawalls under earthquake conditions

To understand the serviceability aspects of seawalls, it is essential to study the permanent displacements of seawalls that occur during the earthquakes. Studies in the existing literature have concentrated on displacements of retaining walls with dry backfills; to the authors’ observation there is no specific analytical investigation devoted to the earthquake-induced displacements of retaining walls with submerged backfills. This paper focuses on sliding displacements of gravity type seawall retaining a submerged backfill under active earth pressure condition during the earthquakes. The threshold seismic acceleration coefficients required for initiation of sliding and the amount of sliding displacement due to seismic loading are calculated by adopting Newmark’s sliding block method. One of the prime features of the study is the estimation of seismic inertia forces in the submerged soil and wall applying the modified pseudo-dynamic method. The comparison of the results obtained using the proposed analytical formulation with the existing literature found to be in good agreement. A comprehensive parametric study has been conducted to understand the effects of different parameters such as seismic horizontal and vertical acceleration coefficients, soil and wall friction angles, width of the wall, wall inclination and excess pore water pressure ratio.

The Wall Friction Properties of Pharmaceutical Powders, Blends, and Granulations

Data from wall friction testing and physical property characterization of over 100 pharmaceutical powders, blends, and granulations have been analyzed. The analyses focused on data for stainless steel surfaces with the most common finishes for pharmaceutical powder processing equipment, either a 2B cold rolled mill finish or an electropolished 2B surface. Active pharmaceutical ingredients exhibited the highest friction against these surfaces, whereas active granulations exhibited the least friction. The typical (median) wall friction angle for an active blend on 2B stainless steel was 22° versus 18° for an active granulation. Typical wall friction values on electropolished 2B surfaces were about 17° and 12° for active blends and granulations, respectively. Blends typically exhibited larger wall friction angles than the granulations suggesting that simple blends will usually require hoppers or bins with steeper walls to achieve mass flow. Lower wall friction angles were consistently observed against the smoother electropolished 2B surface, and, thus, the wall surface finish should be considered when designing bins and hoppers for use with pharmaceutical powders. The wall friction angles of blends and granulations did not show any definite trend as the percentage of active pharmaceutical ingredient increased.

A modified logarithmic spiral method for determining passive earth pressure

In this study, a modified logarithmic spiral method is proposed to determine the passive earth pressure and failure surface of cohesionless sloping backfill, with presence of wall–soil interface friction. The proposed method is based on a limit equilibrium analysis wherein the assumed profile of the backfill failure surface is a composite of logarithmic spiral and its tangent. If the wall–soil interface is smooth, a straight line does not need to be assumed for the failure surface. The geometry of the failure surface is determined using the Mohr circle analysis of the soil. The resultant passive earth thrust is computed considering equilibrium of moments. The passive earth pressure coefficients are calculated with varied values of soil internal friction angle and cohesion, wall friction angle and inclination angle, and sloping backfill angle. This method is verified with the finite element method (FEM) by comparing the horizontal passive earth pressure and failure surface. The results agree well with other solutions, particularly with those obtained by the FEM. The implementation of the present method is efficient. The logarithmic spiral theory is rigorous and self-explanatory for the geotechnical engineer.

Impact of blend properties on die filling during tableting

Based on characterization of a wide range of fillers and APIs, thirty divergent blends were composed and subsequently compressed on a rotary tablet press, varying paddle speed and turret speed. The tablet weight variability was determined of 20 grab samples consisting of each 20 tablets. Additionally, the bulk residence time, ejection force, pre-compression displacement, main compression force, die fill fraction and feed frame fill fraction were determined during each run. Multivariate data analysis was applied to investigate the relation between the process parameters, blend characteristics, product and process responses. Blends with metoprolol tartrate as API showed high ejection forces. This behavior could be linked to the high wall friction value of metoprolol tartrate. The main responses related to the die filling could be predicted via a PLS model based on blend characteristics. Tablet weight variability was highly correlated with the variability on pre-compression displacement and main compression force. A good predictive model for tablet weight variability was obtained taking the porosity, wall friction angle, flowability, density, compressibility and permeability into account. Additionally, turret speed and paddle speed were included in the calibration of the model. The applied approach can save resources (material, time) during early drug product development.