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<br />08/8/00
<br />ENGINEERING INDE% PROPERTIES
<br />Erdnote •• ENGINEERING INDE% PROPERTIES
<br />This report gives estimates of the engineering classification and of the range of index properties for the
<br />major layers of each soil in the survey area. Most soils have layers of contrasting properties within the upper
<br />5 or 6 feet.
<br />DEPTH to the upper aM lower boundaries of each layer is indicated. The range in depth and informatl on on other
<br />properties of each layer are given in the published Soil Survey for each soil series under "Soil Series end Their
<br />Morphology."
<br />TE%TURE is given in the standard terms used by the U. S. Department of Agriculture. These terms are defined
<br />according to percentages of card, 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 />percent sand. If the content of particles coarser than sand is as much as about 15 percent, an appropriate modifier is
<br />added, for example, "gravelly." Textural terms are defined in [he Soil Survey Glossary.
<br />Classification of the soils is determined according to the Unified soil classification system and the eystem
<br />adopted by the American Association of State Xighway and Transportation Officials.
<br />The UNIFIED system classifies soils according to properties that effect [heir use as construction material. Soils are
<br />classified according to grain-size distribution of the fraction less than 3 inches in dian~ter and according to
<br />pl as[ici[y index, liquid limit, and organic matter content. Sandy and gravelly soils are identified as GN, GP, GN, GC,
<br />SN, SP, SM, and SC; silty and clayey soils as ML, CL, OL, MN, LH, and OH; and highly organic soils as PT. Soils
<br />exhibiting engineering properties of two groups can have a dual classification, for example, LL•NL.
<br />The AASHiO system classifies soils according to those properties [hat affect roadway construction and maintenance.
<br />In this system, the fraction of a mineral soil that is less than 3 inches in diameter is classified in one of seven
<br />groups tram A-1 through A-7 an 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). A[ 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 />data 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 />5, or A•7-b. 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 [he best subgrade material to 20 or higher for the poorest.
<br />Rock 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 />percentage.
<br />Percentage of soil particles passing designated sieves (PERCENTAGE PASSING SIEYE NUMBER--)is [he percentage of the
<br />soil fraction less than } inches in diameter based on an ovendry weight. The sieves, numbers 4, 10, 40, end 200 (USA
<br />Standard Series), have openings of 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 estimates made in the field.
<br />LIQUID LIMIT and PLASTICITY INDE% (Atterberg limits) indicate the plasticity characteristics of a soil. The
<br />estimates are based on test data from the survey area or from nearby areas and on field examination. The estima [es
<br />of grain-size distribution, liquid limit, and plasticity index are generally rounded to the nearest 5 percent. Thus,
<br />if the ranges of gradation and Atterber9 limits extend a marginal amount (1 or 2 percentage points) across
<br />classification boundaries, the classification in the marginal zone is omitted in this report.
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