Wall Friction Angle Research Articles

Applications of AMT (Angle Measure Technique) in image analysis: Part II: Prediction of powder functional properties and mixing components using Multivariate AMT Regression (MAR)

This paper presents a novel way to predict the bulk powder characteristics from unilaterally illuminated powders using Angle Measure Technique (AMT) image analysis in combination with multivariate calibration. It is demonstrated that the AMT transform can account for the complexity of images in the scale domain and be used as a strong preprocessing facility for multivariate regression modeling. The concept of multivariate AMT regression has been proposed for this purpose. A wide variety of types of powders was collected in order to study the reliability, reproducibility and representativity of the methods. PLS models have been established to quantitatively predict key physical and behavioral powder properties such as particle size, density, minimum fluidization velocity, wall friction angle, and angle of repose. Finally, a first attempt at prediction of mixing component fractions in powder mixtures has also been implemented, which can be used for on-line monitoring of many types of mixing process if fast digital imaging is available.

00/01537 Effect of centre coke charging on shape of deadman in blast furnace

The mechanism of deadman renewal by centre coke charging was investigated using a 1 :15 scale model of POSCO's Pohang No. 3 blast furnace. The deadman shape in the two-dimensional model could be predicted on the basis of the assumption of an active state in the packed bed. The deadman height depended mainly on the amount of fine powder accumulated in the deadman because the internal and wall friction angles of coke varied according to the amount of fine powder. The deadman was renewed differently according to the ratio of centre coke charging width r c to throat radius R, the critical value of which was found to be 0 . 12. Test operation for centre coke charging under r c /R> 0 . 12 conditions resulted in an improvement in central gas flow and a reduction in heat loss. The renewal period of the deadman was estimated to be about two weeks in an actual blast furnace.

An experimental study of the behaviour of embedded lengths of cantilever walls

Laboratory-based 1–g experiments are described which model the embedded length of cantilever walls in sand, and in which the shear and normal stresses between the soil and the wall were measured, together with wall displacements, as the load on the wall was progressively increased to failure. The results show that comparatively large earth pressures, associated with high effective angles of wall friction, are mobilized just below the soil surface in front of the wall. Earth pressures on the retained side, below the centre of rotation of the wall, were smaller than Rankine passive values, confirming Krey's original views on the downwards direction of wall friction at this location. The results fit well within the relatively small available data set for free embedded cantilever walls, and show the trend of increasing bending moment with depth of embedment, given a constant effective angle of friction.

The effect of interface properties on retaining wall behaviour

A series of finite element analyses have been undertaken to investigate the effects of interface properties on the behaviour of a vertical retaining wall and the deformation of the ground around it. The boundary between a rigid embedded wall and the soil is modelled with zero thickness interface elements. Uniform translation of the wall has been studied. The analyses show the predicted limiting active and passive pressure on the wall are dependent on the maximum wall friction angle and are in reasonable agreement with accepted approximate analytical solutions. The limiting pressure is independent of the stiffness and dilation properties of the interface elements. The dilation properties of the interface have a significant effect on the ground surface deformation around the wall. © 1998 John Wiley & Sons, Ltd.

Laboratory Experiments with an Oblique Passive Wall and Rigid Plasticity Solutions

ABSTRACT Theoretical predictions for passive earth pressure have been developed by some researchers based on the rigid plasticity theory. However, those predictions have yet to be adequately confirmed by experiments particularly for the case of a large wall oblique angle α and large wall friction angle δ. In this paper, the results of laboratory passive earth pressure model tests are compared with predictions based on the rigid plasticity theory. The purpose of this paper is to examine how far the rigid plasticity theory can be applied to passive earth pressure problems. The test results demonstrated that the observed failure zone was similar to that predicted by the characteristics method based on the rigid plasticity theory. Except for the lowest part of the passive wall, the earth pressure increased linearly with depth. For a small wall friction angle δ, passive earth pressure coefficients Kp were almost equal to the theoretical predictions, whereas in the case of a large angle δ those were smaller than the theoretical ones. Because of this difference, progressive failure is suggested. It was demonstrated in the figures of strain distribution and displacement contours of the sand before the peak load.

Full-Scale Field Trials of Tire Shreds as Lightweight Retaining Wall Backfill Under At-Rest Conditions

A 4.88-m (16-ft), full-scale retaining wall test facility was constructed to investigate the use of tire shreds as backfill for conventional retaining walls. The facility can test backfill at at-rest and active conditions and is instrumental for measuring horizontal stress and interface shear. Tire shreds from three suppliers were tested. The results for at-rest conditions are presented. The average at-rest horizontal stress for tire shreds was about 45 percent less than expected for conventional granular backfill. Moreover, the at-rest horizontal stress was about the same for tire shreds from the three suppliers. Design parameters were developed by using two procedures. The first used the coefficient of lateral earth pressure and the other was based on equivalent fluid pressure. The horizontal and shear forces acting on the concrete face of the wall were used to determine the angle of wall friction, which ranged from 30° to 32° for tire shreds from the three suppliers.

受働土圧に関する実験的研究 : その2 乾燥砂地盤における剛性壁の受慟土圧の発生機構について

Passive earth pressure tests of a wall were performed in terms of three variations in displacement: when the wall rotates about its bottom, and when the wall rotates about its top, and the wall is translated. The followings are the results obtained through the test. (1) The passive earth pressure is not found to be in agreement with those obtained Coulomb and Terzaghi theories in either method of displacement (2) The moving wall friction angle δ_c, when the total horizontal earth pressure is at its maximum, is lower than the friction angle between sand and wall in either mothod of dieplacement.

PASSIVE PRESSURE DETERMINATION BY METHOD OF SLICES

A method of slices satisfying all the conditions of statical equilibrium has been developed to deal with the problem of determination of passive earth pressure over a retaining wall in sand. A method similar to that of Morgenstern and Price 1 which was used to solve the stability of slopes, has been followed. The earth pressure coefficients with the proposed methodology have been computed for a vertical retaining wall for both positive and negative wall friction angle. Also examined is the variation of the interslice shear force between the retaining wall and the Rankine Passive boundary. Due to complete satisfaction of the equilibrium conditions, the method generates exactly the same earth pressure coefficients as computed by using Terzaghi's overall limit equilibrium approach.

Passive pressure coefficients, critical failure surface and its kinematic admissibility

Using a combination of a logarithmic spiral and a straight line as a failure surface, comprehensive charts have been developed to determine the passive earth pressure coefficients and the positions of the critical failure surface for positive as well as negative wall friction angles. Translational movement of the wall has been examined in detail, considering the soil as either an associated flow dilatant material or a non-dilatant material, to determine the kinematic admissibility of the limit equilibrium solutions.

Pressure exerted by a granular material along a curved channel

The method of characteristics by Sokolovski is extended to find the stresses exerted by a granular material along a curved channel. As the grain flow develops, the granular material is considered under the criterical state of plastic equilibrium. The state of stress on any plane within the granular material may be represented by a Mohr circle in the τ-σ plane, and a continuous solution of stress distribution can then be obtained by applying the method of characteristics, which is based on the equations of equilibrium and the Mohr-Coulomb yield criterion. Wall stresses obtained from this method are compared with previous research of stress distribution with vertical walls and are considered to be reasonable. It is suggested that this simple numerical analysis is suitable for estimating stresses on a curved wall and can be used in structural design. Some numerical results are given in graphical form in terms of the effective angle of internal friction of the granular material ϱ and the angle of wall friction δ.

Experimental and numerical study of sand–steel interfaces

AbstractExperimental and numerical studies on and sand–steel interfaces are presented. Emphasis is laid on the effect of boundary conditions of the whole system and of localized deformation. The experiments with different roughness of steel surface, sand density, normal stress and grain size are carried out in a plane strain apparatus, a parallely guided direct shear apparatus and in a planar silo model with a movable bottom and parallel steel walls. During the test in the plane strain apparatus the localized zone is observed with the help of X‐rays. The results indicate a significant effect of wall roughness and boundary conditions of the whole system on the wall friction angle and the thickness of the localized zone along the steel surface.An elastoplastic constitutive model established within the framework of a Cosserat continuum, capable of describing isotropic hardening, softening and dilatancy, is implemented in a finite element code. The model differs from the conventional theory of plasticity due to the presence of Cosserat rotation and couple stress using the mean grain diameter as the characteristic length. Finite element simulations of simple shear tests are presented. The additional boundary condition along the steel plate, characteristic of the Cosserat continuum, allows for modelling the different roughness of the steel plate with consideration of grain rotations. A comparison between the numerical calculations and the experimental results shows acceptable agreement.

Micro-Mechanical modelling of load dependent friction in contacts of elastic spheres

Recent experimental measurements using twin-axis load cells in storage vessels for bulk solids have revealed load-dependent variation of the wall friction angles measured in the presence of small normal loads on smooth silo walls. The effect is quite appreciable with smooth particles such as plastic beads and glass ballotini, but particles with rough surfaces, like some agricultural seeds, show no such effect.The inclusion of an intrinsic shear resistance at zero normal load into the frictional behaviour (after Briscoe and Tabor) provides a satisfactory prediction of tangential forces required to cause gross sliding of smooth particles over smooth silo walls. This work applies the same adhesive friction concepts to the microdisplacements that occur before full tangential sliding develops.Mindlin analysed the traction profiles for two spheres in contact assuming a constant coefficient of friction, independent of normal stress inside the contact area, with microslip occurring in those portions of the contact area that had a tangential-to-normal stress ratio exceeding the friction coefficient. The assumptions of that analysis preclude the existence of the observed load dependence of wall friction angles. In this paper we re-examine the micromechanical nature of contacts between elastic spheres incorporating tangential stress limits that contain two terms: one proportional to the normal stress at each point in the contact area, the other independent of normal stress. Two possible physical (and mathematical) interpretations of the stress-independent term are discussed, one called adhesive slip and the other stick slip. The resulting traction profiles are examined to determine implications for both microslip and gross-sliding frictional behaviour. A complete theoretical analysis requires the solution of the surface displacement integral over the contact region for a chosen form of the tangential traction profile satisfying appropriate boundary conditions for elastic displacements. Upper and lower bounds and an approximate form for the resulting tangential force-displacement curves are developed and it is shown that such models result in a load-dependent friction behaviour that is very similar to recent experimental wall friction and individual particle friction measurements.

Driving Characteristics of Open‐Toe Piles in Dense Sand

Driving tests are conducted on large‐scale steel model pipe piles with open toes to determine how geometric configurations of the toes affect driving performance. A further objective is to investigate a wave‐equation model for predicting driveability of open‐toe piles in dense, saturated sand. The tests are conducted in a large pressure chamber. Examination of the experimental data and of finite element analyses of the problem indicate that pipes with thickened and beveled toes require less energy for penetration than plain, cylindrical pipes, and that none of the piles plug solidly during driving up to penetrations of 21 diameters into the dense layer. It is found that the angle of wall friction on the interior of the pipe is a major factor in controlling the plug movement. One‐dimensional wave‐equation simulations of the tests are found to be adequate, but only with empirical adjustment of parameters related to static resistance.

A Lower-Bound Approach to Active and Passive Earth Pressure Problems

ABSTRACT Active and passive earth pressures acting on retaining walls are known to be a complicated function of many factors, for instance, the cohesion and friction angle of backfill material, wall friction, and geometries of wall and backfill. Conventional theories based on stability analysis, e.g., Coulomb and Rankine methods which are now quite widely used, cannot necessarily take all these factors into consideration. Firstly this paper develops a numerical procedure for calculating active and passive earth pressures against rigid retaining walls, which enables to take account all these factors affecting active and passive pressures, and which presents full information about the earth pressures. Secondly, by comparing the procedure with Coulomb and Rankine methods, this paper aims to clarify the mechanical and practical meanings of these classical methods. Based on the lower–bound theorem in the theory of plasticity, the procedure searches the minimum and maximum values respectively of active and passive thrusts within the limitations of satisfying the equilibrium equations and non–failure condition. To represent these conditions, the earth pressure and the stress field within backfill are discretized in a similar manner as in the finite element method. On the problem formulation, two methods are considered depending on whether a potential slip surface is assumed or not. When assuming a slip surface, arises a serious difficulty that the criterion for locating the critical slip surface is contrary to the criterion for determining the stress field. When assuming no slip surface,. it is shown that the proposed procedure provides the reasonable solutions of active and passive pressures and that the boundary condition of wall and backfill movements has an essential meaning in the analysis. The procedure is applied to a number of case studies, where comparisons are made thoroughly with classical theories. Through the development of the procedure, many important aspects in the earth pressure problems are clarified.

Influence of capsule dosator wall texture and powder properties on the angle of wall friction and powder-wall adhesion

The influence of capsule dosator wall texture and powder properties on the angle of wall friction and powder-wall adhesion was investigated using a modified annular shear cell. Powder-wall friction studies were conducted for different size fractions of five pharmaceutical excipients and two dosator wall materials of defined textures. Results indicate that the angle of wall friction (Φ) and powder-wall adhesion are functions of the powder material, its particle size and the dosator wall roughness. For a particular excipient, smaller values of Φ are generally observed for coarser size fractions and a smoother wall surface.

高炉内装入物の運動に関する理論解析と冷間模型実験

The characteristics of burden flow in blast furnace is discussed based on both theoretical analyses and observations in two types of cold model experiments with gas blowing. Sublimation of dry ice particles is utilized in the experiments to simulate coke combustion before tuyeres or the volume reduction of cohesive layers in blast furnace. Experimentally observed profile of deadman, which is formed just behind the raceway, is shown to be in good agreement with a slip line calculated for the passive stress state. Theoretical height of the deadman is increased by decreased angle of internal friction and increased angle of wall friction. The burden flow in the shaft is approximately described by a potential flow theory taking account of the volume change of burden. Below the lower end of the shaft, however, the viscous flow analysis gives more realistic flow field presumably due to the prevailing passive stress state.

石炭バンカーの閉塞に対する改良ホッパおよび壁材の効果

Experiments were carried out on the discharge of wet coals from experimental bunkers with a capacity of about 4m3. These bunkers were reduced to a scale of one-sixth the actual size of those in a coal thermal power station. Consequently, the coal bunker must be completely designed as a type of mass flow.An improved hopper was proposed in order to reduce the critical size of hopper outlet. The improved hopper was a regular pyramidal hopper joined to a conical hopper, and a prismatic insert was installed between each opposite wall of the pyramidal hopper.A method is described for the estimation of the critical size of the bridge in the hoppers at the commencement of flow on the basis of the conditions of the static state of stresses exerted by the bulk solid. The estimated values of the critical outlet size, using the fixed volume shear cell results, were in good agreement with the experimental results of the discharge.The experimental results also indicate that the slope angle of the hopper walls was reasonably determined from both the angle of internal friction and the angle of wall friction according to Jenike's approach. Moreover, remnants of coal that adhered to the bunker walls were strongly affected by the wall materials used, such as steel and ultra high molecular weight polyethylene.

An alternative presentation of the design parameters for mass flow hoppers

The procedure for determining the critical hopper outlet dimension and wall slope for mass flow hoppers by the Jenike method is well established and documented. However, existing presentations relating the bulk solid flow properties of effective angle of internal friction and the kinematic angle of wall friction with the hopper wall slope and flow factor for mass flow are often inconvenient for manual use and present difficulties when included in design programs suitable for microcomputers. This paper details an alternative presentation of the original Jenike flow factor charts. These alternative charts have been abbreviated to display only the critical design values in the border region between mass flow and funnel flow. The charts eliminate the need for imprecise parameter interpolations by displaying the required design parameters in the form of contours of constant wall slope and critical flow factor as a function of the effective angle of internal friction and the kinematic angle of wall friction. An illustrative example is provided to demonstrate the inherent advantages of this presentation for the evaluation of mass flow hopper geometries.

The Influence of Particle Attrition on the Wall Friction Coefficient of a free flowing particulate solid

AbstractIn this paper a reciprocating shear cell, which has been developed to measure dynamic wall friction, is described. The cell has also been used to study the attrition behaviour of sand samples at the bounding wall. This attrition causes a considerable change in the angle of wall friction.

Einfluß der Wandreibung auf die Dimensionierung von Bunkern — Verfahrenstechnische und statische Gesichtspunkte

AbstractInfluence of wall friction on the design of silos – Aspects of process technology and statics. Mass flow and funnel flow are distinguished when considering the discharge of stored bulk solids. In order to cause mass flow to occur, i. e. the complete bunker filling is in motion, hopper walls need to be steep. Conditions close to the outlet are decisive, a large value of wall friction requiring steep hopper walls. For a safe design of bunker walls with respect to mechanical strength, DIN 1055, part 6 is commonly applied; it is currently being revised. From this regulation a strong influence of the angle of wall friction can be inferred, small values of the angle being associated with high horizontal pressures. In case the angle of wall friction depends on pressure and other parameters and safety factors are included there may be a considerable difference between the angle used by a process engineer and by a civil engineer.