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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. <br />