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ORANGE COUNTY, NORTH CAROLINA
<br />The ratings in the engineering tables are based on test
<br />data and estimated data in the "Soil Properties" section.
<br />The ratings were determined jointly by soil scientists and
<br />engineers of the Soil Conservation Service using known
<br />relationships between the soil properties and the behavior
<br />of soils in various engineering uses.
<br />Among the soil properties and site conditions identified
<br />by a soil survey and used in determining the ratings in
<br />this section were grain-size distribution, liquid limit,
<br />plasticity index, soil reaction, depth to bedrock, hardness
<br />of bedrock that is within 5 or 6 feet of the surface, soil
<br />wetness, depth to a seasonal high water table, slope,
<br />likelihood of flooding, natural soil structure or aggrega-
<br />tion, in-place soil density, and geologic origin of the soil
<br />material. Where pertinent, data about kinds of clay
<br />minerals, mineralogy of the sand and silt fractions, and
<br />the kind of absorbed cations were also considered.
<br />On the basis of information assembled about soil pro-
<br />perties, ranges of values can be estimated for erodibility,
<br />permeability, corrosivity, shrink-swell potential, available
<br />water capacity, shear strength, compressibility, slope sta-
<br />bility, and other factors of expected soil behavior in en-
<br />gineering uses. As appropriate, these values can be ap-
<br />plied to each major horizon of each soil or to the entire
<br />profile.
<br />These factors of soil behavior affect construction and
<br />maintenance of roads, airport runways, pipelines, founda-
<br />tions for small buildings, ponds and small dams, irrigation
<br />projects, drainage systems, sewage and refuse disposal
<br />systems, and other engineering works. The ranges of
<br />values can be used to: (1) select potential residential, com-
<br />mercial, industrial, and recreational uses; (2) make
<br />preliminary estimates pertinent to construction in a par-
<br />ticular area; (3) evaluate alternative routes for roads,
<br />streets, highways, pipelines, and underground cables; (4)
<br />evaluate alternative sites for location of sanitary landfills,
<br />onsite sewage disposal systems, and other waste disposal
<br />facilities; (5) plan detailed onsite investigations of soils
<br />and geology; (6) find sources of gravel, sand, clay, and
<br />topsoil; (7) plan farm drainage systems, irrigation
<br />systems, ponds, terraces, and other structures far soil and
<br />`-.water conservation; (8) relate performance of structures
<br />already built to the properties of the kinds of soil on
<br />which they are built so that performance of similar struc-
<br />tures on the same or a similar soil in other locations can
<br />be predicted; and (9) predict the trafficability of soils for
<br />cross-country movement of vehicles and construction
<br />equipment.
<br />'. "Data presented in this section are useful for land-use
<br />R; planning and for choosing alternative practices or
<br />`general designs that will overcome unfavorable soil pro-
<br />perties and minimize soil-related failures. Limitations to
<br />the use of these data, however, should 6e well understood.
<br />First, the data are generally not presented for soil
<br />material below a depth of 5 or 6 feet. Also, because of the
<br />scale of the detailed map in this soil survey, small areas
<br />of soils that differ from the dominant soil may be in-
<br />~:,clz~ded in mapping. Thus, these data do not eliminate the
<br />r,:
<br />need for onsite investigations, testing, and analysis E
<br />personnel having expertise in the specific use conten
<br />plated.
<br />The information is presented mainly in tables. Table
<br />shows, for each kind of soil, the degree and kind of limit<
<br />tions for building site development; table 7, for sanitar
<br />facilities; and table 9, for water management. Table
<br />shows the suitability of each kind of soil as a source c
<br />construction materials.
<br />The information in the tables, along with the soil mal
<br />the soil descriptions, and other data provided in this suz
<br />vey can be used to make additional interpretations and t
<br />construct interpretive maps for specific uses of land.
<br />Some of the terms used in this soil survey have a ape
<br />cial meaning in soil science. Many of these terms are
<br />defined in the Glossary.
<br />Building Site Development
<br />The degree and kind of soil limitations that affect shal
<br />low excavations, dwellings with and without basements
<br />small commercial buildings, and local roads and street:
<br />are indicated in table 6. A slight limitation indicates that
<br />soil properties are favorable for the specified use; any
<br />limitation is minor and easily overcome. A moderatE
<br />limitation indicates that soil properties and site feature,
<br />are unfavorable for the specified use, but the limitations
<br />can be overcome or minimized by special planning and
<br />design. A severe limitation indicates that one or more soil
<br />properties or site features are so unfavorable or difficult
<br />to overcome that a major increase in construction effort,
<br />special design, or intensive maintenance is required. For
<br />some soils rated severe, such costly measures may not be
<br />feasible.
<br />Shallow excavations are made for pipelines, sewerlines,
<br />communications and power transmission lines, basements,
<br />open ditches, and grave sites. Such digging or trenching is
<br />influenced by soil wetness caused by a seasonal high
<br />water table; the texture and consistence of soils; the ten-
<br />dency of sails to cave in or slough; and _ the presence of
<br />very firm, dense soil layers, bedrock, or large stones. In
<br />addition, excavations are affected by slope of the soil and
<br />the probability of flooding. Ratings do not apply to sail
<br />horizons below a depth of 6 feet unless otherwise noted.
<br />In the soil series descriptions, the consistence of each
<br />soil horizon is defined, and the presence of very firm or
<br />extremely firm horizons, usually difficult to excavate, is
<br />indicated.
<br />Dwellings and small commercial buildings referred to
<br />in table 6 are built on undisturbed soil and have a founda-
<br />tion load of a dwelling no more than three stories high.
<br />Separate ratings are made for small commercial buildings
<br />without basements and fbr dwellings with and without
<br />basements. For such structures, soils should be suffi-
<br />ciently stable that cracking or subsidence of the structure
<br />from settling or shear failure of the foundation does not
<br />occur. These ratings were determined from estimates of
<br />the shear strength, compressibility, and shrink-swell
<br />
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