Effective Internal Friction Angle Research Articles

Flow Properties of F icus Deltoidea Extract Powder and the Binders, Acdisol and Avicel

This work aimed to investigate the flowability properties of the basic powders used to make tablets by means of direct compression. The main product in this study is Ficus deltoidea extract powder, while the excipients operated as binder were croscarmellose sodium (NaCMC or Acdisol) and microcrystalline cellulose (MCC or Avicel). Such excipient powders are essentially water insoluble and can also act as a filler, disintegrator and dissolver in tablet form. In order to compare and optimize powders regarding flowability, a Jenike shear tester was used to measure the flow properties of the powder particle, such as the effective angle of internal friction, flow function and the angle of wall friction. The experimental results showed higher flow property values for binders compared with F. deltoidea extract powder. These results provide essential information for the processing and handling of these powders during storage, transportation and also for the next processing step of powder – tabletting. Practical Applications Ficus deltoidea is a popular herb in Malaysia and has become an international favorite for its health-giving properties and nutritional benefits. This medicinal plant is locally known as Mas Cotek or serapat angin, telinga beruk and other few names. It is a valuable herbal plant that grows wild in the tropical forest of Malaysia, which has become an international favorite for its medicinal and healthy values. As a herbal tree, almost all of the parts of F. deltoidea plant including the roots, bark, stems, leaves and fruits are believed to have medicinal properties, which is useful for health purposes. Due to their promising and high commercial potential, the herb is studied to further develop their scientific usage in terms of pharmaceutical dosage (tablet). However, a small number of scientific work have been conducted to investigate the flow and physical properties of F. deltoidea. However, empirical knowledge and fundamental understanding of the relative contribution of flow properties of F. deltoidea extract powder to neutraceutical industries is lacking. Knowledge of flowabilities of this herb may improve its handling and processing and the quality of tablet production, particularly its mechanical properties.

Stability Analysis of Unsaturated Soil Slopes Based on Unified Strength Theory

Based on the unified solution of shear strength in terms of double stress state variables for unsaturated soils, the unified formula of stability coefficient for unsaturated soil slopes under the plane strain condition is derived by Sweden slice method, which considers the effect of the intermediate principal stress rationally. Combining with engineering example, the proposed formula is compared with the one that is on the basis of Fredlund unsaturated soil theory and the influencing characteristics of factors including intermediate principal stress, matric suction, effective internal friction angle and matric suction angle is obtained. The research result indicates that: intermediate principal stress and matric suction have obvious impacts on the stability coefficient for unsaturated soil slopes; the stability coefficient has been increasing with the increase of unified strength theory parameter and matric suction, which proves that the consideration of intermediate principal stress and matric suction can make slopes give full play to their self-stabilities and strength potential, and the yield criterion has great impact on the judgment of slope stability; the stability coefficient also increases nonlinearly with the increase of effective internal friction angle and matric suction angle. The proposed unified formula of stability coefficient for unsaturated soil slopes enjoys a wider application. The stability coefficient for unsaturated soil slopes according to the Fredlund unsaturated soil theory and that for saturated soil slopes are just the special cases. The research result can provide theoretical basis for stability analysis and reinforce design of the unsaturated soil slopes, and it is of great significance to the slope management.

Strength behavior of slip-zone soils of landslide subject to the change of water content

Landslides are the major natural hazards in many countries all over the world and are usually caused by heavy rainfall, water level change of reservoir, excavation, earthquake, etc. Whether the landslide occurs or not in rainfall season, the strength variation of slip-zone soils of landslide is regarded as the vital control factor. Thus, strength behavior for slip-zone soils of landslide subject to the change of water content is required to be evaluated in a potential landslide area. In this paper, the shear strength of typical slip-zone soil, six groups of 25 specimens of remolded clay samples from Daxishan reservoir landslide, was systemically investigated using the improved direct shear test apparatus in order to fully understand its physical and mechanical properties, and also the shear and failure behavior. Furthermore, the fitting equations for expressing the relationship between the shear strength (effective cohesion and internal friction angle) and vertical loadings, initial water contents of slip-zone clay were established based on the experimental results. In particular, a series of shear stress–shear strain curves under various vertical loadings and different water contents were observed. The results show that a “softening” stress–strain behavior is achieved for unsaturated slip-zone soil, while a “hardening” curve is found for saturated slip-zone soil.

Test Study on Strength Characteristics of Unsaturated Silt

A series of consolidation and drainage unsaturated triaxial tests on remolded samples were carried out at controlled matrix suction and confining pressure through automatic GDS triaxial apparatus. According to the shear strength of unsaturated silt, the results show the matrix suction has a little influence on effective angle of internal friction, while has great influence on failure modes and cohesion. With the increasing of matrix suction, stress-strain curves translate from hardening type to softening type, the effective angle of internal friction changes a little and is approximately equal to the effective angle of internal friction of saturated soil, cohesion is significantly improved. Matrix suction friction angle is not a constant, when the matrix suction is less than 100kPa, it decreases with matrix suction increasing, the rate of decrease reduces gradually; when matrix suction is greater than 100kPa, it tends to be a fixed value. The results are consistent to modified strength theory proposed by Fredlund.

Unified Solution of Coulomb’s Active Earth Pressure for Unsaturated Soils without Crack

Based on the unified solution of shear strength in terms of double stress state variables for unsaturated soils, whilst considering the effect of the intermediate principal stress rationally, the unified solution of Coulomb’s active earth pressure for unsaturated soils without cracks is developed. Comparability of the solution is analyzed and influencing characteristic of each factor is obtained. The research result indicates that: the intermediate principal stress and matric suction have obvious impacts on Coulomb’s active earth pressure for unsaturated soils; Coulomb’s active earth pressure has been decreasing until zero with the increase of unified strength theory parameter and matric suction; Coulomb’s active earth pressure increases with the increase of grading angle of retaining wall and slop angle of backfill, but decreases with the increase of matric suction, effective internal friction angle and matric suction angle, while external friction angle has no obvious influence. The proposed unified solution of Coulomb’s active earth pressure enjoys a wider application, and unified solution of Rankine’s active earth pressure is just the special case. The results are of great significance to soil pressure determination such as slope and foundation pit, and to retaining structures design.

The Mechanical Parameters of Rapeseed Cake

The objective of the reported project was to investigate the mechanical properties of rapeseed cake and its mixture with wheat meal obtained under various conditions of extrusion. The density, the angle of internal friction, the effective angle of internal friction, the cohesion, the flow function, and the modulus of elasticity were determined.

Effect of Low Temperature Air Plasma Treatment on Wetting and Flow Properties of Kaolinite Powders

It was found in this study that the air plasma treatment of particular kaolinite has led to the change of its wettability, which was reflected in the decreased values of water contact angles of wetting from 88.7° for virgin kaolinite to 86.3° for 30 min air plasma treated one. Plasma treated samples show higher average surface energies in the wide range of coverage regimes in comparison to the virgin samples as determined by inverse gas chromatography. Results of these measurements confirmed our assumption, that air plasma treatment activates surface energy of the crystal planes of the kaolinite as reflected in the broadened dispersive surface energy distribution after 10 min treatment time. However with prolonged 30 min treatment time the dispersive surface energy distribution profile was decreased. We assume, that the latter decrease reflects the distorsion of the crystal lattice of the kaolinite as confirmed by FTIR analysis as reflected in changes of Si–O–Si and Al2O–H characteristic absorption bands. Calculated dispersive surface free energy for 24 % surface coverage was increased from original 35 mJ/m2 to 40.3 and 40.8 mJ/m2 for 10 and 30 min treatment times. There were determined yield locus and flow function dependencies at different stress levels for virgin and different time plasma treated samples (flow index—ffc, effective angle of internal friction—φe, unconfined yield strength—σc). It was found that by plasma treatment the character of the flow was shifting from region of very cohesive (ffc = 2.39) to the cohesive (ffc = 3.19). For untreated samples effective angle of internal friction was decreased with increasing applied consolidation stress, while for plasma treated kaolinite it was increased.

Flow properties of three fuel powders

Flow and physical properties were measured for three fuel powders: sawdust, brown coal and hard coal. Besides physical properties, e.g., particle size, bulk density and moisture content, flowability was investigated using the standard shear testing technique of the Jenike shear cell. Flow functions of the three powders used for characterization of bulk flow and design of hoppers were determined, and then compared and discussed. The flow functions of the three powders are located in different regions: while brown coal and hard coal were classified respectively as easy flowing and cohesive material, sawdust was found in regions varying from cohesive to easy flowing at low consolidation stress. The measured effective angle of internal friction and angle of wall friction were 55° and 31.4° for sawdust; 36.2° and 26° for brown coal; and 43.3° and 27.8° for hard coal. Using the measured powder flow properties, Jenike's procedure was then followed to estimate and compare the critical hopper dimensions for mass flow of the three powders.

Instrumented roll technology for the design space development of roller compaction process

Instrumented roll technology on Alexanderwerk® WP120 roller compactor was developed and utilized successfully for the measurement of normal stress on ribbon during the process. The effects of process parameters such as roll speed (4–12rpm), feed screw speed (19–53rpm), and hydraulic roll pressure (40–70bar) on normal stress and ribbon density were studied using placebo and active pre–blends. The placebo blend consisted of 1:1 ratio of microcrystalline cellulose PH102 and anhydrous lactose with sodium croscarmellose, colloidal silicon dioxide, and magnesium stearate. The active pre-blends were prepared using various combinations of one active ingredient (3–17%, w/w) and lubricant (0.1–0.9%, w/w) levels with remaining excipients same as placebo.Three force transducers (load cells) were installed linearly along the width of the roll, equidistant from each other with one transducer located in the center. Normal stress values recorded by side sensors and were lower than normal stress values recorded by middle sensor and showed greater variability than middle sensor. Normal stress was found to be directly proportional to hydraulic pressure and inversely to screw to roll speed ratio. For active pre-blends, normal stress was also a function of compressibility. For placebo pre-blends, ribbon density increased as normal stress increased. For active pre-blends, in addition to normal stress, ribbon density was also a function of gap.Models developed using placebo were found to predict ribbon densities of active blends with good accuracy and the prediction error decreased as the drug concentration of active blend decreased. Effective angle of internal friction and compressibility properties of active pre blend may be used as key indicators for predicting ribbon densities of active blend using placebo ribbon density model. Feasibility of on-line prediction of ribbon density during roller compaction was demonstrated using porosity–pressure data of pre-blend and normal stress measurements. Effect of vacuum to de-aerate pre blend prior to entering the nip zone was studied. Varying levels of vacuum for de-aeration of placebo pre blend did not affect the normal stress values. However, turning off vacuum completely caused an increase in normal stress with subsequent decrease in gap.Use of instrumented roll demonstrated potential to reduce the number of DOE runs by enhancing fundamental understanding of relationship between normal stress on ribbon and process parameters.

Effect of low temperature air plasma treatment on physico-chemical properties of kaolinite

It was found in this study that air plasma treatment of particular kaolinite has led to the change of its wettability. This was reflected in the decreased values of water contact angles of wetting. There were determined yield locus and flow function dependencies at different stress levels for virgin and different time plasma treated samples (flow index - ffc, effective angle of internal friction - phie, unconfined yield strength - sigmac). It was found that by plasma treatment the character of the flow was shifting from region of very cohesive (ffc = 2.39) to the cohesive (ffc = 3.19). For untreated samples effective angle of internal friction was decreased with increasing applied consolidation stress, while for plasma treated kaolinite it was increased.

Seismic Passive Earth Pressure with Seepage for Cohesionless Soil

The authors deal with the computing seismic passive earth pressure acting on a vertical rigid wall. The wall is provided with a drainage system along soil-structure interface and retains the cohesionless backfill subjected to water seepage. A general solution for the seismic passive earth pressure is presented. The solution is based on Coulomb's theory wherein seismic forces are assumed to be pseudostatic. The solution considers the pore water pressures induced by water seepage and earthquake shaking. Some important parameters are included in the solution. The parameters are the soil effective internal friction angle, wall friction, soil unit weight, and horizontal and vertical seismic acceleration coefficients. The comparison of the total seismic passive earth pressure in horizontal direction from the present method with published works indicates that the present method may be reasonable. The variations of the passive earth pressure coefficient with the soil effective internal friction angle are investigated for different wall friction angles and seismic forces. The effect of the water seepage on the seismic passive earth pressure is also investigated.

Modeling the powder roll compaction process: Comparison of 2-D finite element method and the rolling theory for granular solids (Johanson's model)

This study compares the nip angle, normal stress at the roll gap, and the maximum material relative density computed from 2-D finite element method (FEM) simulations and the 1-D Johanson's model for roll compaction of powders. In general, the nip angles predicted from the Johanson model follow the same trends as those from the FEM model. Both predictions agree to within 25% using typical pharmaceutical material properties. However, the compact densities predicted by the Johanson model are greater than one regardless of the operating conditions or material parameters. As shown in the FEM model, this unrealistic result is due to a two-dimensional velocity gradient that is not accounted for in the Johanson model. Finally, the normal stresses in the roll gap predicted by the Johanson model are generally larger than those found using the FEM model. The two approaches agree better when the material is more compressible, has a lower effective internal friction angle, a larger roll-powder friction angle, and when the streamwise inlet normal stress decreases.

The measurement of powder flow properties with a mechanically stirred aerated bed

This paper re-examines a set of experimental data published by Bruni et al. (2007a, 2007b) [Bruni, G., Barletta, D., Poletto, M., Lettieri, P., 2007a. A rheological model for the flowability of aerated fine powders. Chem. Eng. Sci. 62, 397–407; Bruni, G., Lettieri, P., Newton, D., Barletta, D., 2007b. An investigation of the effect of the interparticle forces on the fluidization behaviour of fine powders linked with rheological studies. Chem. Eng. Sci. 62, 387–396] carried out on a mechanically stirred fluid-bed rheometer (msFBR), which was developed to study the rheology of aerated and fluidized powders. The use of aeration below fluidization allowed to carry out experiments with powders at very low consolidation levels. Two mathematical models, based on the Janssen approach to evaluate stresses in powder containers, were developed in order to relate the torque measurements in the Fluidized Bed Rheometer to the flow properties of the powders measured with standard powder flow testers. Results indicate that the models were able to satisfactorily predict the torque measured by the msFBR. The larger complexity of the Walker (1966) [Walker, D.M., 1966. An approximate theory for pressures and arching in hoppers, Chem. Eng. Sci. 21, 975–997] and Walters (1973) [Walters, J.K., 1973. A theoretical analysis of stresses in silos with vertical walls, Chem. Eng. Sci. 28, 13–21] stress analysis adopted in one of the two models did not introduce significant improvements in the evaluation of the stress distribution to justify its use. A procedure for the inverse application of the model was developed and applied to estimate the powder flow properties starting from msFBR data. The application of this procedure provided good results in terms of effective angle of internal friction and is promising for the ability of the system to explore powder flow at very low consolidation states.

Reproducibility of flow properties of microcrystalline cellulose — Avicel PH102

Earlier work showed that a batch of microcrystalline cellulose (MCC, Avicel PH102) exhibited minimum acceptable flow properties required for successful high speed tableting. The aim of this work was to assess the suitability of using Avicel PH102 as a reference indicator of minimum powder flow by examining the reproducibility of flow properties of seven batches of Avicel PH102. Powder flow properties have been characterized in terms of flow function, flow factor, cohesion, bulk density, effective angle of internal friction, angle of linearized yield locus, and angle of internal friction at steady-state flow. Results show that the measured flow function is independent of operator. Batch-to-batch flow functions are not statistically different at 95% confidence level suggesting acceptable reproducibility. These results corroborate that Avicel PH102 may be used as a reference powder for predicting flow performance of a new formulation during high speed tableting.

Practical implications of theoretical consideration of capsule filling by the dosator nozzle system.

Eight lactose size fractions with mean particle sizes ranging from 15.6 to 155.2 micrometers were characterized by their failure properties using a Jenike shear cell. The effective angle of internal friction was found to be constant for all size fractions, with a mean value of 36.2 degrees. Jenike flow factors could only be obtained for the two most cohesive size fractions presumably due to limitations of the shear cell. Angles of wall friction, phi, were determined for all size fractions on face ground and turned stainless steel surfaces. These decreased with increasing particle size up to around 40 micrometers, above which they became effectively constant for both surfaces. The rougher turned plate gave consistently higher values of phi for each particle size. Simple retention experiments with a dosator nozzle and a range of powder bed bulk densities showed good retention was possible only up to a particle size of around 40 micrometers. Retention was difficult or impossible above this size. Values of phi were applied to equations derived in the theoretical approach described previously (Jolliffe et al 1980). This showed that the strength required within a powder to ensure arching increases with increasing particle size up to around 40 micrometers. Above this size, this strength requirement becomes constant. This is related to the powder retention observations. Finally, the failure data was used to calculate the minimum compressive stresses required to ensure powder retention within the dosator nozzle, by employing the equations described by Jolliffe et al (1980). This suggested that, as powders became more free flowing, a larger compressive stress is necessary and that the angle of wall friction should be lower to ensure stress is transmitted to the arching zone.

Modelling the applied vertical stress and settlement relationship of shallow foundations in saturated and unsaturated sands

The bearing capacity and settlement of foundations are determined experimentally or modelled numerically based on conventional soil mechanics for saturated soils. In both methods, bearing capacity and settlement are estimated based on the applied vertical stress versus surface settlement relationship. These methods are also conventionally used for soils that are in an unsaturated condition, ignoring the contribution of matric suction. In this study, a methodology is proposed to estimate the bearing capacity and settlement of shallow foundations in unsaturated sands by predicting the applied vertical stress versus surface settlement relationship. The proposed method requires soil parameters obtained under only saturated conditions (i.e., effective cohesion, effective internal friction angle, and modulus of subgrade reaction from model footing test) along with the soil-water characteristic curve (SWCC). In addition, finite element analyses are undertaken to simulate the applied vertical stress versus surface settlement relationship for unsaturated sands. The proposed method and finite element analyses are performed using an elastic – perfectly plastic model. The predicted bearing capacities and settlements from the proposed method and finite element analyses are compared with published model footing test results. There is good agreement between measured and predicted results.

Temporal evolution of weathered cataclastic material in gravitational faults of the La Clapiere deep-seated landslide by mechanical approach

After a few years of research, the observation and the analysis of the deep-seated landslides suggest that these are mainly controlled by tectonic structures, which play a dominant role in the deformation of massif slopes. The La Clapiere deep-seated landslide (Argentera Mercantour massif) is embedded in a deep-seated gravitational slope deformation affecting the entire slope, and characterized by specific landforms (trenches, scarps…). Onsite, the tangential displacement direction of the trenches and the scarps are controlled by the tectonic structures. The reactivation of the inherited fault in gravitational faults create a gouge material exposed to an additional mechanical and chemical weathering as well as an increased of leaching. The displacement of these reactivated faults gets increasingly important around the area of the La Clapiere landslide and this since 3.6 ka BP. In this study, mechanical analysis and grain size distributions were performed and these data were analysed according to their proximity the La Clapiere landslide and times of initiation of the landslide by 10Be dating. Triaxial test results show that the effective cohesion decreases and the effective angle of internal friction increases from the unweathered area to the weathered area. The whole distribution of the grain size indicates that the further the shear zone is open or developed, the further the residual material loses its finest particles. This paper suggests that the mechanical evolution along the reactivated fault is influenced by the leaching processes. For the first time, we can extract from these data temporal behaviour of the two main mechanical parameters (cohesion and angle of internal friction) from the beginning of the La Clapiere landslide initiation (3.6 ka BP) to now.

Preparing Very Loose Granular Triaxial Specimens by Ex Situ Freezing

Abstract Ex situ soil freezing can be used to prepare very loose cohesionless triaxial specimens that can be handled, stored, and transported. This paper describes two freezing techniques, freezing with cold air in a freezer and freezing with liquid nitrogen. These methods are used to prepare very loose saturated Ottawa sand specimens. Special equipment and techniques used for each method are described. The advantages and disadvantages of both methods and the effectiveness of the efforts to minimize disturbance due to volume changes during freezing are discussed. Properties of specimens prepared using each method are presented. The results of 16 consolidated undrained triaxial shear tests are presented. The freezing method affects the amount of volume change during freezing but does not significantly affect the effective angle of internal friction.

Assessment of the Undrained Response of Sands under Limited and Complete Liquefaction

The technique presented deals with the assessment, based on drained test behavior and formulation, of the undrained postcyclic stress-strain behavior of sands under limited or complete (full) liquefaction and its associated strength. At present, there is no particular procedure that allows assessment of such undrained postcyclic behavior that could develop full (pore-water pressure ratio, ru=1) or limited (ru<1) liquefaction. The prediction of the undrained postliquefaction (full or limited liquefaction) response presented here is based on basic properties of sand such as its relative density (Drc) [or (N1)60 blowcount], the effective angle of internal friction (φ), the roundness of the sand grains (ρ), and the drained axial strain at 50% stress level (ε50). The technique presented accounts for the excess pore-water pressure induced by cyclic loading (Δuc) and the postcyclic excess pore-water pressure generated under undrained monotonic loading (Δud).

Interactive software for calculating the principal stresses of compacted cohesive powders with the Warren-Spring equation

The Unconfined Yield Stress ( σ c) and Major Consolidation Stress ( σ 1) of a cohesive powder′s compact are found by constructing two Mohr semicircles that are tangential to the Yield Loci Curve (YLC); the first passing through the origin (0,0) and the second at the consolidation conditions ( σ 0, τ 0). When the YLC can be described by the Warren-Spring equation ( τ/ C) n = ( σ + Τ)/ Τ or an alternative algebraic expression, this translates into finding the solution of two pairs of simultaneous equations that set the conditions for the tangential YLC and corresponding Mohr semicircles to have the same value and slope at their respective contact points. Once the Mohr semicircle′s equation that corresponds to the consolidation conditions has been found, the Effective Angle of Internal Friction ( δ) is calculated in a similar manner. The numerical calculation procedure has been automated in a freely downloadable program posted on the web as a Wolfram Project Demonstration. It allows the user to choose and adjust the values of C, T, n and σ 0, and the plot′s scales, by moving sliders on the computer screen. The program calculates and displays the corresponding values of σ c, σ 1 and δ, and plots the YLC, two Mohr semicircles and the line that defines δ. Since a linear YLC is just a special case of the model where n = 1, the program can be used with input parameters originally obtained by linear regression. But although the program can render reasonable estimates of the principal stresses σ c , σ 1 and δ in this case too, the physical meaning of C, and especially T, is unclear when calculated by extrapolation instead of being determined experimentally.