Fill dirt is earthy material which is used to fill in a depression or hole in the ground or create mounds or otherwise artificially change the grade or elevation of real property.
Fill dirt is usually subsoil (soil from beneath the top soil) and underlying soil parent material which has little soil organic matter or biological activity. Fill dirt is taken from a location where soil is being removed as a part of leveling an area for construction; it may also contain sand, rocks, and stones, as well as earth.
Fill dirt should be as free of organic matter as possible since organic matter will decompose creating pockets of empty space within the fill which could result in settling. Uneven or excessive settling of the fill can result in damage to any structures built on the fill.
A common use of fill dirt is in highway maintenance to build up the shoulders of highways so that the ground on either side of the pavement is at the same level as the pavement itself and that the highway shoulders are sufficiently wide as to allow vehicles room to pull off of the highway if needed.
A second common use of fill dirt is to fill in a low lying construction site to raise the level of the building foundation in order to reduce the chances of flooding. Several massive uses of fill dirt are with improvements to the Port of Seattle Sea-Tac Airport, the addition of a new runway to the Hartsfield-Jackson Atlanta International Airport in Atlanta, Georgia, and the Shin Kansai Kuko or New Osaka Airport off the coast of Japan, a project involving the creation of a new man-made island of some five square kilometers.
Fill dirt is also used for landscaping projects which involve the creation of ridges and earth structures for pools, waterfalls, and other water features as well as to break up a level area in order to provide more interesting textures to the landscape.
See also 
- "Fill dirt" Industry Terms and Definitions, EMG, retrieved on 2008-11-12.
- "Advisory Legal opinion: Definition and disposal of dirt" Attorney General of Florida, March 19, 1982
- "Free Clean Fill dirt listing site. Connecting people with dirt.
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