| ullage | The space in the upper part of a bulk storage container that cannot be filled because of the surface contours formed by the repose conditions acting from the point of fill. |
| unconfined failure | The failure of a particulate bed that is not supported on a boundary by a confining surface, therefore no normal force or shear force is acting on this surface. Such is the situation at the underside of an arch. |
| under-consolidated | A state of consolidation and applied stress where shearing causes compaction of the particulate structure in the shear plane. |
| uniaxial state of stress | State of stress in which two of the principal stresses are zero. |
| unloading module | Slope of the tangent to the unloading stress-strain curve at a given stress value. |
| van der Waal forces | Molecular attractive forces between closely aligned fine particles. |
| viscous flow | Of permeability. A form of flow in which adjacent layers of fluid do not mix except at the molecular level and when the velocity at the particle interface is zero. |
| void | Space in a particulate bed that is not occupied by particulate matter. This volume may be occupied by air, water or any other liquid or gas in any combination. If the void space is totally occupied by a liquid, the bed is said to be ‘fully saturated’. |
| void pressure | The pressure of the fluid, usually air, in the interstitial voids between the particles in a bed. |
| void ratio | The ratio of the volume of the void space to the volume of the solid particles in a given particulate mass. At higher normal loads, with a particular condition of preparation, the shear strength will not peak, and continue to increase accompanied by an increase in the density of the sample to a different bulk condition, where it has a greater shear strength. See underconsolidated. |
| void pressure | The pressure of the fluid, usually air, in the interstitial voids between the particles in a bed. |
| void ratio | The ratio of the volume of the void space to the volume of the solid particles in a given particulate mass. At higher normal loads, with a particular condition of preparation, the shear strength will not peak, and continue to increase accompanied by an increase in the density of the sample to a different bulk condition, where it has a greater shear strength. See underconsolidated. |
Glossary of Terms in Powder & Bulk Technology
1.3 General Terms
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