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Engineering Properties--Weld County,Colorado,Northern Part Koskie Pit 2020 Amendment
<br /> Texture is given in the standard terms used by the U.S. Department of
<br /> Agriculture. These terms are defined according to percentages of sand, silt, and
<br /> clay in the fraction of the soil that is less than 2 millimeters in diameter. "Loam,"
<br /> for example, is soil that is 7 to 27 percent clay, 28 to 50 percent silt, and less than
<br /> 52 percent sand. If the content of particles coarser than sand is 15 percent or
<br /> more, an 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, GM, GC, SW, SP, SM, and SC; silty and clayey soils as ML, CL, OL, MH,
<br /> CH, and OH; and highly organic soils as PT. Soils exhibiting engineering
<br /> properties of two groups can have a dual classification, for example, CL-ML.
<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
<br /> soil that is less than 3 inches in diameter is classified in one of seven groups
<br /> from A-1 through A-7 on the basis of particle-size distribution, liquid limit, and
<br /> plasticity index. Soils in group A-1 are coarse grained and low in content of fines
<br /> (silt and clay). At the other extreme, soils in group A-7 are fine grained. Highly
<br /> organic soils are 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
<br /> classified as A-1-a, A-1-b, A-2-4, A-2-5, A-2-6, A-2-7, A-7-5, or A-7-6.As an
<br /> additional refinement, the suitability of a soil as subgrade material can be
<br /> indicated by a group index number. Group index numbers range from 0 for the
<br /> best subgrade material to 20 or higher for the poorest.
<br /> Percentage of rock fragments larger than 10 inches in diameter and 3 to 10
<br /> inches in diameter are indicated as a percentage of the total soil on a dry-weight
<br /> basis. The percentages are estimates determined mainly by converting volume
<br /> percentage in the field to weight percentage. Three values are provided to
<br /> identify the expected Low(L), Representative Value (R), and High (H).
<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
<br /> sieves, numbers 4, 10, 40, and 200 (USA Standard Series), have openings of
<br /> 4.76, 2.00, 0.420, and 0.074 millimeters, respectively. Estimates are based on
<br /> laboratory tests of soils sampled in the survey area and in nearby areas and on
<br /> estimates made in the field. Three values are provided to identify the expected
<br /> Low(L), Representative Value (R), and High (H).
<br /> Liquid limit and plasticity index(Atterberg limits) indicate the plasticity
<br /> characteristics of a soil. The estimates are based on test data from the survey
<br /> area or from nearby areas and on field examination. Three values are provided to
<br /> identify the expected Low(L), Representative Value (R), and High (H).
<br /> References:
<br /> American Association of State Highway and Transportation Officials (AASHTO).
<br /> 2004. Standard specifications for transportation materials and methods of
<br /> sampling and testing. 24th edition.
<br /> USDA Natural Resources Web Soil Survey 3/24/2020
<br /> Conservation Service National Cooperative Soil Survey Page 2 of 6
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