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Bearing capacity
Published in R.F. Craig, Craig’s Soil Mechanics, 2004
The density index of loose to medium-dense sand deposits can be increased by the process of vibrocompaction. The technique employs a depth vibrator suspended from the jib of a crane or carried on special mountings, typical vibrators having lengths of 3–5 m and diameters of 300–450 mm. The vibrator section is located at the lower end of, and isolated from, the main body of the unit. The vibrator, which can be hydraulically or electrically powered, operates with a gyratory motion in a horizontal plane, produced by the rotation of eccentric masses. The unit penetrates the soil under its own weight, usually assisted by jets of water emitted from the conical point of the vibrator. The combined effects of vibration and water jetting induce local liquefaction of the adjacent soil, enabling the unit to penetrate readily under its own weight. After reaching the required depth, jetting is halted or reduced, the vibrator is gradually withdrawn and the surrounding soil is compacted by the horizontal vibratory action. The process creates a conical depression at the surface which is continuously filled with granular material, either from the site or imported, as the vibrator is withdrawn. Significant compaction of the soil can usually be achieved to a radius of up to 2.5 m from the axis of the vibrator, depending on the particle size distribution and initial density of the soil and the characteristics of the equipment. The soil should be compacted to at least the significant depth of the foundations in question, depths up to 12 m having been treated. The process is repeated at suitable spacings over the area in question creating a soil mass of increased bearing capacity. Vibrocompaction cannot be used in fine soils, especially saturated clays, because the vibrations would be damped within a relatively small radius. The process may be less efficient if the soil has a significant content of fine sand and non-plastic silt particles.
Effect of Lubricant Properties and Contact Conditions on False Brinelling Damage
Published in Tribology Transactions, 2023
Rachel Januszewski, Victor Brizmer, Amir Kadiric
Experiments to investigate the influence of various lubricant properties and contact conditions on the damage due to small amplitude oscillating motion were performed using a PCS Instruments high-frequency reciprocating rig (HFRR) shown in Fig. 2. In this rig a 6-mm-diameter ball specimen is reciprocated against the flat surface of a disc under oscillating amplitudes as low as 20 μm. Oscillating motion is provided by an electromagnetic vibrator. The drive system permits variation in both amplitude and frequency of oscillation and the normal load is varied mechanically using weights. A linear variable differential transducer measures linear displacement in order to control the stroke length, and a fretting flexure lock ensures accuracy at stroke lengths below 100 μm. The temperature of the test cell is controlled through a heater block. The system records frictional force and electrical contact resistance. The electrical contact resistance provides an indication of the prevalent lubrication conditions in the contact throughout the tests (20), which greatly aids the interpretation of observed fretting wear trends.