S. DEPARTMENT OF AGRICULTURE PAGE 2 OF 2
<br /> TURAL RESOURCES CONSERVATION SERVICE 01/28/97
<br /> ' ENGINEERING INDEX PROPERTIES
<br /> �dnote -- ENGINEERING INDEX PROPERTIES
<br /> This report gives estimates of the engineering classification and of the range of index properties for the
<br /> )or layers of each soil in the survey area. Most soils have layers of contrasting properties within the upper
<br /> or 6 feet.
<br /> pPTH to the upper and Lower boundaries of each layer is indicated. The range in depth and information on other
<br /> roperties of each layer are given in the published Soil Survey for each soil series under "Soil Series and Their
<br /> Morphology."
<br /> 1XTURE is given in the standard terms used by the U.S. Department of Agriculture. These terms are defined
<br /> cording to percentages of sand, silt, and clay in the fraction of the soil that is less than 2 millimeters in
<br /> diameter. "Loam," for example, is soil that is 7 to 27 percent clay, 28 to 50 percent silt, and less than 52
<br /> rcent sand. If the content of particles coarser than sand is as much as about 15 percent, an appropriate modifier is
<br /> dad, for example, "gravelly." Textural terms are defined in the Soil Survey Glossary.
<br /> assification of the soils is determined according to the Unified soil classification system and the system
<br /> opted by the American Association of State Highway and Transportation Officials.
<br /> The UNIFIED system classifies soils according to properties that affect their use as construction material. Soils are
<br /> �assified according to grain-size distribution of the fraction less than 3 inches in diameter and according to
<br /> asticity index, Liquid limit, and organic matter content. Sandy and gravelly soils are identified as GW, GP, GM, GC,
<br /> SW, SP, SM, and SC; silty and clayey soils as ML, CL, OL, MH, CH, and ON; and highly organic soils as PT. Soils
<br /> Ihibiting engineering 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 roadway construction and maintenance.
<br /> � this system, the fraction of a mineral soil that is less than 3 inches in diameter is classified in one of seven
<br /> oups from A-1 through A-7 on the basis of grain-size distribution, Liquid limit, and plasticity index. Soils in
<br /> group A-1 are coarse grained and low in content of fines (silt and clay). At the other extreme, soils in group A-7
<br /> are fine grained. Highly organic soils are classified in group A-8 on the basis of visual inspection. If laboratory
<br /> Ita are available, the A-1, A-2, and A-7 groups are further classified as A-1-a, A-1-b, A-2-4, A-2-5, A-2.6, A-2-7, A-7-
<br /> or A-7-6. As an additional 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 to 20 or higher for the poorest.
<br /> Ick FRAGMENTS larger than 3 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 percentage in the field to weight
<br /> Ircentage.
<br /> rcentage of soil particles passing designated sieves (PERCENTAGE PASSING SIEVE NUMBER--)is the percentage of the
<br /> soil fraction less than 3 inches in diameter based on an ovendry weight. The sieves, numbers 4, 10, 40, and 200 (USA
<br /> �andard Series), have openings of 4.76, 2.00, 0.420, and 0.074 millimeters, respectively. Estimates are based on
<br /> boratory tests of soils sampled in the survey area and in nearby areas and on estimates made in the field.
<br /> �QUID LIMIT and PLASTICITY INDEX (Atterberg limits) indicate the plasticity characteristics of a soil. The
<br /> timates are based on test data from the survey area or from nearby areas and on field examination. The estimates
<br /> of grain-size distribution, liquid Limit, and plasticity index are generally rounded to the nearest 5 percent. Thus,
<br /> lthe ranges of gradation and Atterberg limits extend a marginal amount (1 or 2 percentage points) across
<br /> assification boundaries, the classification in the marginal zone is omitted in this report.
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