Vibratory Densification Research Articles

Closure to “Passive Earth Pressure with Critical State Concept” by Yung-Show Fang, Ying-Chieh Ho, and Tsang-Jiang Chen

The authors should be congratulated for synthesizing the results of an interesting experimental investigation on the passive earth pressure on retaining walls. The authors have used these experimental results as a guide in developing design procedures. In their tests, the authors have adopted a sand placing technique, namely by placing the sand in thin layers and then applying surface compaction on each layer to achieve the required unit weight and angle of shearing resistance of the sand. It is evident that the application of vibratory densification produces an overconsolidation effect in the sand mass. Depending on the level of energy transferred to a given layer, the in situ stress level in the said layer will increase. The energy transferred depends on the thickness of the placed sand layer, compaction effort applied on the surface of each layer, compaction duration, and the order of the respective layer ~the energy input for a lower layer is the total of the energy applied to the said layer plus the energy transferred to this layer during compaction of the subsequent layers!. The energy transferred to a given layer reflects on the in situ stress level and accordingly, the value of the overconsolidated ratio ~OCR! of the said layer ~Hanna and Ghaly 1990; Hanna and Soliman-Saad 2001!. The OCR has a direct and significant effect on the coefficients of earth pressure ~Hanna and Soliman-Saad 2001; Bellotti 1976; Feda 1984; Brooker and Ireland 1965!. The authors have treated the produced sand beds in the laboratory as if they were normally consolidated; i.e., the case of OCR51. The authors have reported that the experimental test results agreed well with both Coulomb and Terzaghi theories for the case of loose sand, while a wide disagreement was noted for the case of dense sand ~using the peak angle of shearing resistance of the sand!. In treating this problem, the authors have proposed to adopt the residual-internal angle of friction of the sand, instead of the peak angle of shearing resistance. As expected, by reducing the angle of shearing resistance to the residual value ~which is equivalent to the ultimate value for the case of loose sand! agreement will be achieved with Coulomb and Terzaghi theories. In implementing such assumption the authors have allowed a wall movement of about 10–20% of the height of the wall for medium to dense sand respectively. Such high wall displacement may not be allowed in statically indetermined structures such as bridges. Furthermore, beyond the peak angle of shearing resistance, f, the inter-particles stresses will be the dismantled due the dilation ~Hanna 2001!. Thus, the in situ stress level will be reduced and accordingly the OCR will reach the value for normally consolidated sand (OCR51). This procedure suggests that sands at all

Geotechnical Behavior of JSC-1 Lunar Soil Simulant

To facilitate the modeling and simulation of lunar activities and natural processes, various lunar soil simulants have been created. In particular, Johnson Space Center Number One lunar soil simulant (JSC-1) has come into wide use by a variety of investigators. In any physical experiment, the behavioral properties of this simulant will have a profound impact on the results. To better understand these soil properties, a variety of conventional and unconventional experiments were conducted on JSC-1 to determine its friction angle and appropriate low strain elastic constants. These experiments were conducted on JSC-1 at a variety of relative densities to quantify the response of the soil over the range of possible conditions. Further, the samples were prepared through vibratory densification, allowing for a better simulation of probable lunar surface packing arrangements.

Ground vibrations from sheetpile driving in urban environment: measurements, analysis and effects on buildings and occupants

Following a comprehensive review of the subject of man-made ground vibrations, measurements of ground vibration caused by vibratory sheetpile driving in recent soil deposits are reported in terms of particle velocities vs. distance from the source of vibration. The measurements were conducted on paved surfaces and sidewalks in the inner urban environment. Reconstructed particle displacement paths indicated, predominantly, vertical vibrations of the Rayleigh type. The attenuation rate of vibrations with distance was compared to published results of other studies and satisfactory agreement was found to exist. Values of particle velocity measured in this study, however, were lower than corresponding values of other studies under comparable values of rated vibratory kinetic energy. This is possibly due to different soil conditions. Average and upper bound linear log–log attenuation relationships are proposed, which fit the results of measurements and are representative of the conditions likely to be encountered in the urban environment. Measurement of vibrations on higher floors of multistory reinforced concrete buildings indicated a significant amplification of vertical vibration and an average curve for amplification magnitude vs. floor level was fitted to the results of measurements. A comparison of measured values of vibration with the observed performance of buildings and with damage threshold values suggested by existing codes and standards indicated that the latter do not provide safety against damage caused by vibratory densification of loose sandy soils. On the other hand, the existing criteria for human exposure to vibrations in buildings, according to the results of this study, seem to adequately define the degrees of human discomfort.

Vibratory densification of thermal insulation corundum products

During vibratory densification, the bulk density and the angle of repose of the corundum bodies based on hollow granules and a porous filler depend on the type of the filler used and the size of its grains. The relative settling and the relative density of the bodies obtained after densification are related to their bulk density and the angle of repose.

Bronze filters for air purification in automobiles

A study was made of the sintering of bronzes with varying amounts of phosphorus, up to 1%. The optimum phosphorus content, at which pores do not decrease in size or become blocked and no crack formation occurs, was found to be 0.3%. To enable sintered filters to be attached strongly to other components, the portions of filters used for fastening should be made from finer powders. The feasibility is demonstrated of producing filters composed of several layers of powders differing in particle size; the pouring of each powder fraction is followed by vibratory densification in the mold, sintering being performed after the whole multilayer part has been built up. Filters produced by the methods described are characterized by satisfactory air permeability and strength.

Effect of vibration and current pulses on the shaping of powder mixtures

1. The optimum conditions have been determined, using the method of extreme experiment planning, for the vibratory densification of a 50% carbonyl nickel + 50% carbonyl iron powder mixture. 2. It is demonstrated that 40-μsec EST at j =30 kJ effectively fixes the particles of powders subjected to vibratory pressing.

Characteristics and mechanism of vibratory densification of sand and role of acceleration : Tokue, T Soils Found, V16, N3, Sept 1976, P1–18

Characteristics and mechanism of vibratory densification of sand and role of acceleration : Tokue, T Soils Found, V16, N3, Sept 1976, P1–18

Characteristics And Mechanism of Vibratory Densification of Sand And Role of Acceleration

Vertical vibration tests with a rigid mold as well as dynamic and cyclic simple shear tests were conducted on sand to investigate the characteristics and mechanism of densification. Vertical acceleration was applied to the sample in the vertical vibration tests, but the dynamic stress was very small relative to the confining stress. Dynamic and cyclic simple shear tests were conducted by using the same simple shear apparatus. Both dynamic shear stress and horizontal acceleration were given to the sample in the dynamic simple shear tests. Cyclic simple shear tests were conducted under the following two kinds of conditions to investigate the role of acceleration in the densification of sand by vibration. (1) Only the cyclic shear stress, whose amplitude was equal to that of the dynamic shear stress, was given to the sample by stress controlling. (2) The shear strain amplitudes, which were equal to those in the dynamic simple shear tests, were given to the sample by strain controlling. From all these results, it was recognized that vibratory acceleration participated in the densification of sand by vibration in two ways. One was as an average dynamic stress and the other was as body force applied directly to each grain of sand. When dynamic shear stress became the dominant factor, the body force and the damping resistance in a sample had respective influences on the densification of sand to a degree that was not negligible. Moreover, the relationship between the volume change and the shear strain was not significantly affected by the values of overburden pressures and accelerations or the randomness of shear strain amplitudes.

Some results of an investigation into the vibratory densification of metal powders in a vibratory press

Some results of an investigation into the vibratory densification of metal powders in a vibratory press

Vibratory densification of dispersion-type fuel elements for nuclear reactors

Theoretical calculations are given of the distribution of particle sizes and weight proportions of individual fractions necessary for the attainment of maximum density in tubular, annular, and “inversed” fuel elements as a result of vibratory densification. It is shown that, in the attainment of a high and uniform packing density, of vital importance are the ratios between the dimensions of the shell of the vessel and the diameter of the coarse-fraction particles, and also of the particle sizes of the remaining fractions. The particles of these fractions must fit the residual interstitial voids, whose distribution is not uniform even in tubular fuel elements. Measurements, made with a gamma-ray meter, have demonstrated that there is good agreement between actual and calculated axial density distributions. It seems reasonable to assume that the procedure described should make it possible to obtain, in some cases at any rate, the relatively uniform packing density that is required in the compaction of metal powder parts of complex configuration.

Effect of inertia loading on the vibratory densification of powder materials

Effect of inertia loading on the vibratory densification of powder materials

Manufacture of porous chromium carbide materials by the method of vibratory densification

1. The vibratory method of shaping enables thin-walled porous chromium carbide parts to be produced having a more uniform pore size than that obtained in sintering loosely poured powders. 2. Vibratory densification employing oscillations of triangular pulse form and a static load of 40 g/ cm2 applied by means of an inertia mass is more effective than vibratory densification with a static load of 6–8 kg/cm2 applied by compressed springs, in the production of high-permeability porous materials having isometric pores. Additional advantages of the former method are that less power is consumed in it and cheaper, low-strength dies can be used.

Vibratory Densification of Damp Clayey Sands

The vibratory densification characteristics of damp clayey sands are investigated experimentally in an extensive series of approximately 350 tests, in which 0.6 cu ft samples of air-dry or damp sand or sand-clay mixtures were subjected to vertical vibrations at various amplitudes and frequencies under three conditions of confining stress. The physical parameters of interest are the maximum density obtained and the rate at which densification occurs. The test results are presented in graphical form, and comparisons are made with the maximum density values obtained from conventional compaction tests conducted in accordance with ASTM D 1557-66T (Modified Proctor) for the different soils. Several quantitative and qualitative conclusions are drawn from the test data; in particular, the water content of the soil was found to exert a major influence on the maximum density obtained by vibratory densification.

Free vibratory densification of SAP powders

Free vibratory densification of SAP powders

Vibratory densification as a means of increasing the strength of compacts

A study was made of the vibratory densification of a bismuth-molybdenum catalyst (with a corundum filler, taken in a weight ratio of 1∶1). It was found that compared with static compaction vibratory densification enables the pressure to be reduced by a factor of about 100, sharply decreases internal stresses, and ensures greater packing density (4.0 g/cm3 against 3.75 g/cm3 in static compaction). It also leads to a 100% increase in the strength of fine-particle, high-porosity catalyst specimens without adversely affecting their catalytic activity.

Production of parts by vibratory compacting

1. Compared with the vibrating punch scheme, the vibrating container scheme secures a higher quality of compacts. 2. Using the method of free vibratory densification, it is possible to produce parts with a high heightto-diameter ratio (H/D> 6), a relative density of 73% or less in the sintered condition, and a strictly uniform density distribution over the compact height. 3. By applying vibratory densification to spherical powder systems consisting of two fractions it is possible to obtain parts with a high height-to-diameter ratio, a relative density of 85% or less, and a uniform density distribution over the compact height. 4. The use of vibratory densification before static compaction enables parts to be produced with a low height-to-diameter ratio (H/D< 0.1) and a strictly uniform density distribution over the compact surface.

The production and properties of spherical copper powders and parts from such powders

1. Copper powders produced by the methods of plasma spraying and melting of nonspherical powder particles consist of particles which are nearly spherical and have a smooth surface. 2. With the plasma spraying method, copper-wire scrap can be used for producing spherical powder. This method gives a high percentage yield of spherical particles; by regulating conditions of preparation, it is possible to alter the quantitative yield of any powder fraction. 3. The method of powder preparation by melting gives a 100% yield of spherical particles; the resultant powder may be made to consist of particles belonging almost exclusively to one fraction. The deviation from the size range of the required fraction is small and does not extend beyond the neighboring fractions. 4. A study of the formation of parts from spherical powders demonstrated that, by employing compacting, it is possible to produce parts of the required porosity, but this is accompanied by particle deformation. With freely poured powder, the residual porosity is 40–50%. Vibratory densification permits the porosity to be lowered to 35%. The use of vibratory densification is particularly effective in the manufacture of thin-walled parts of complex configuration. 5. The vibratory densification of different powder fractions takes place at different frequencies and amplitudes. The vibratory densification process may be intensified by applying low static pressures. 6. A study of materials obtained by sintering powders with a 0.3% phosphorus addition at a temperature of 1000°C demonstrated that the strength properties of materials are independent of the powder preparation method. The bending strength is 35–55 MN/m2.