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Engineering Properties —Mesa County Area, Colorado
<br />Engineering Properties
<br />This table gives the engineering classifications and the range of engineering
<br />C .properties.for the layers.of.each.soil in the. survey area.
<br />Depth to the upper and lower boundaries of each layer is indicated.
<br />Texture is given in the standard terms used by the U.S. Department of Agriculture.
<br />These terms are defined according to percentages of sand, silt, and clay in the
<br />fraction of the soil that is less than 2 millimeters in diameter. "Loam," for example,
<br />is soil that is 7 to 27 percent clay, 28 to 50 percent silt, and less than 52 percent
<br />_sand...lf.the content of-particles coarser -than sand is 15 percent or more, an
<br />appropriate modifier is added, for example, "gravelly."
<br />Classification of the soils is determined according to the Unified soil classification
<br />system (ASTM, 2005) and the system adopted by the American Association of
<br />State Highway and Transportation Officials ( AASHTO, 2004).
<br />The Unified system classifies soils according to properties that affect their use as
<br />construction material. Soils are classified according to particle -size distribution of
<br />the fraction less than 3 inches in diameter and according to plasticity index, liquid
<br />limit, and organic matter content. Sandy and gravelly soils are identified as GW,
<br />GP GC, SW, SP, SM., and.,SC; silty.:and clayey soils as ML, CL, OL, MH, .CH,
<br />and OH; and highly organic soils as PT. Soils exhibiting engineering properties of
<br />two groups can have a dual classification, for example, CL -ML.
<br />USDA Natural Resources Web Soil Survey 2/25/2010
<br />' Conservation Service National Cooperative Soil Survey Page 1 of 7
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<br />The AASHTO system classifies. soils according to those properties that affect
<br />roadway construction and maintenance. In this system, the fraction of a mineral soil
<br />that is less than 3 inches in diameter is classified in one of seven groups from A -1
<br />through A -7 on the basis of particle -size distribution, liquid limit, and plasticity index.
<br />Soils in group A -1 are coarse grained and low in content of fines (silt and clay). At
<br />F-
<br />the other extreme, soils in group A -7 are fine grained. Highly organic soils are
<br />classified in group A -8 on the basis of visual inspection.
<br />If laboratory data are available, the A -1, A -2, and A -7 groups are further classified
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<br />as A -1 -a, A -1 -b, A -24, A -2 -5, A -2 -6, A -2 -7, A -7 -5, or A-7-6. As an additional
<br />refinement, the suitability of a soil as subgrade material can be indicated by a group
<br />index number. Group index numbers range,from 0 for the best subgrade material
<br />to 20 or higher for the poorest.
<br />Rock fragments larger than 10 inches in diameter and 3 to 10 inches in diameter
<br />are indicated as a percentage of the total soil on a dry- weight basis. The
<br />percentages are estimates determined mainly by converting volume percentage in
<br />the field to weight percentage.
<br />Percentage (of soil particles) passing designated sieves is the percentage of the
<br />soil fraction less than 3 inches in diameter based on an ovendry weight. The sieves,
<br />numbers 4, 10, 40, and 200 (USA Standard Series), have openings of 4.76, 2.00,
<br />0.420, and 0.074 millimeters, respectively. Estimates are based on laboratory tests
<br />of soils sampled in the survey area and in nearby areas and on estimates made in
<br />the field.
<br />Liquid limit and plasticity index (Atterberg limits) indicate the plasticity
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<br />characteristics of a soil. The estimates are based on test data from the survey area
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<br />or from nearby areas and on field examination.
<br />USDA Natural Resources Web Soil Survey 2/25/2010
<br />' Conservation Service National Cooperative Soil Survey Page 1 of 7
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