Gravel

For other uses, see Gravel (disambiguation).

Gravel (largest fragment in this photo is about 4 cm)

A gravel road in Terre Haute, Indiana.

Gravel being unloaded from a barge

Gravel is rock that is of a certain particle size range. In geology, gravel is any loose rock that is at least two millimeters (2mm) in its largest dimension (about 1/12 of an inch) and no more than 75 millimeters (about 3 inches). Sometimes gravel is restricted to rock in the 2-4 millimeter range, with pebble being reserved for rock 4-75 millimeters (some say 64 millimeters). The next smaller size class in geology is sand, which is 0.063 mm to 2 mm in size. The next larger size is cobble, which is 75 (64) millimeters to 256 millimeters (about three to ten inches). One cubic foot (28.32 dm³) of gravel typically weighs about 100 pounds (45 kg) [1].

Gravel is an important commercial product, used in many applications.

Many roadways are surfaced with gravel, especially in rural areas where there is little traffic. Globally, far more roads are surfaced with gravel than with concrete or tarmac; Russia alone has over 400,000 km of gravel-surfaced roads.

Contents 1 Geological Formation 2 Etymology 3 Types of gravel 4 See also 5 External links

Geological Formation

Large gravel deposits are a common geological feature, being formed as a result of the weathering and erosion of rocks. The action of rivers and waves tends to pile up gravel in large accumulations. This can sometimes result in gravel becoming compacted and concreted into the sedimentary rock called conglomerate. Where natural gravel deposits are insufficient for human purposes, gravel is often produced by quarrying and crushing hard-wearing rocks, such as sandstone, limestone, or basalt. Quarries where gravel is extracted are known as gravel pits. Southern England possesses particularly large concentrations of them due to the widespread deposition of gravel in the region during the Ice Ages.

Etymology

The word comes from the French gravelle, meaning \'coarse sand\'.

Types of gravel

Gravel with stones sized roughly between 5 and 15 millimeter.

Disused gravel pit in Lower Saxony, Germany

Multiple types of gravel have been recognized, including:

• Bank gravel: gravel intermixed with sand or clay.

• Bench gravel: a bed of gravel located on the side of a valley above the present stream bottom, indicating the former location of the stream bed when it was at a higher level.

• Creek rock: This is generally rounded, semi-polished stones, potentially of a wide range of types, that are dredged or scooped from river beds and creek beds. It is also often used as concrete aggregate and less often as a paving surface.

• Crushed Rock: Rock that is mechanically broken into small pieces then sorted by filtering through different size mesh.

• Crushed stone: This is generally limestone or dolomite that has been crushed and graded by screens to certain size classes. It is widely used in concrete and as a surfacing for roads and driveways, sometimes with tar applied over it. Crushed stone may also be made from granite and other rocks. A special type of limestone crushed stone is dense grade aggregate, or DGA, also known as crusher run. This is a mixed grade of mostly small crushed stone in a matrix of crushed limestone powder.

• Fine gravel: gravel consisting of particles with a diameter of 1 to 2 mm.

• Lag gravel: a surface accumulation of coarse gravel produced by the removal of finer particles.

• Pay gravel: also known as "pay dirt"; a nickname for gravel with a high concentration of gold and other precious metals. The metals are recovered through gold panning.

• Piedmont gravel: a coarse gravel carried down from high places by mountain streams and deposited on relatively flat ground, where the water runs more slowly.

• Plateau gravel: a layer of gravel on a plateau or other region above the height at which stream-terrace gravel is usually found.

• River run gravel: naturally deposited gravel found in and next to rivers and streams.

See also

• Aggregate
• Clay
• Silt
• Sand
• Pebble
• Cobble
• Boulder

External links

• Free advice on Gravel, including free calculators and laying guides

• Free Forum on Gravel and other landscape products. Ask questions about gravel here.

• Gravel Watch: Responsible Management of Aggregates

v • d • e Topics in geotechnical engineering
Soils	Clay · Silt · Sand · Gravel · Peat
Soil properties	Hydraulic conductivity · Water content · Void ratio · Bulk density · Thixotropy · Reynolds\' dilatancy · Angle of repose · Cohesion · Porosity · Permeability · Specific storage
Soil mechanics	Effective stress · Pore water pressure · Shear strength · Overburden pressure · Consolidation · Soil compaction · Soil classification · Shear wave
Geotechnical investigation	Cone penetration test · Standard penetration test · Exploration geophysics · Monitoring well · Borehole
Laboratory tests	Atterberg limits · California bearing ratio · Direct shear test · Hydrometer · Proctor compaction test · R-value · Sieve analysis · Triaxial shear test · Hydraulic conductivity tests · Water content tests
Field tests	Crosshole sonic logging · Nuclear Densometer Test
Foundations	Bearing capacity · Shallow foundation · Deep foundation · Dynamic load testing · Wave equation analysis
Retaining walls	Lateral earth pressure · Mechanically stabilized earth · Soil nailing · Tieback · Gabion · Slurry wall
Slope stability	Mass wasting · Landslide
Earthquakes	Soil liquefaction · Response spectrum · Seismic hazard · Ground-structure interaction
Geosynthetics	Geotextile · Geomembranes · Geosynthetic clay liner
Instrumentation for Stability Monitoring	Deformation Monitoring · Automated Deformation Monitoring

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