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Soil texture is determined by the relative proportion of the three kinds of soil mineral particles, called soil separates: sand, silt, and clay. At the next larger scale, soil structures called peds or more commonly soil aggregates are created from the soil separates when iron oxides , carbonates , clay, silica and humus , coat particles and ...
If the soil has more than 15% by weight retained on a #4 sieve (R #4 > 15%), there is a significant amount of gravel, and the suffix "with gravel" may be added to the group name, but the group symbol does not change. For example, SP-SM could refer to "poorly graded SAND with silt" or "poorly graded SAND with silt and gravel."
However, silt is very vulnerable to erosion, and it has poor mechanical properties, making construction on silty soil problematic. The failure of the Teton Dam in 1976 has been attributed to the use of unsuitable loess in the dam core, and liquefication of silty soil is a significant earthquake hazard. Windblown and waterborne silt are ...
A fourth term, loam, is used to describe equal properties of sand, silt, and clay in a soil sample, and lends to the naming of even more classifications, e.g. "clay loam" or "silt loam". Determining soil texture is often aided with the use of a soil texture triangle plot. [5] An example of a soil triangle is found on the right side of the page.
The AASHTO Soil Classification System was developed by the American Association of State Highway and Transportation Officials, and is used as a guide for the classification of soils and soil-aggregate mixtures for highway construction purposes.
The soil suborders within an order are differentiated on the basis of soil properties and horizons which depend on soil moisture and temperature. Forty-seven suborders are recognized in the United States. [6] The soil great group category is a subdivision of a suborder in which the kind and sequence of soil horizons distinguish one soil from ...
Soil texture triangle showing the USDA classification system based on grain size Map of global soil regions from the USDA. For soil resources, experience has shown that a natural system approach to classification, i.e. grouping soils by their intrinsic property (soil morphology), behaviour, or genesis, results in classes that can be interpreted for many diverse uses.
Soil texture is the analysis and classification of the particle size distribution in soil. The relative amounts of sand, silt, and clay particles determine a soil's texture, which affects the appearance, feel and chemical properties of the soil. [12] Soil texture-by-feel method