Figure 16-2.—Typical soil profile.are planned to take advantage of well-draining soils.Considerations relating to frost action become moreimportant when frost-susceptible soils are shown on theprofile.SOURCES OF INFORMATIONVarious sources of information are available.Published information and previous soil analyses aresources you may secure without field exploration. Timesources are used mostly to locate, within a large generalarea, small areas that you may want to investigatefurther. For final site selection, actual fieldinvestigations must be made. Published informationsources include engineer intelligence reports, geologicand topographic maps and reports, agricultural soilmaps and reports, and air photographs.Intelligence reportsthat include maps and studiesof soil conditions are usually available for areas in whichmilitary operations have been planned. Among the mostcomprehensive of these are the Terrain IntelligenceFolios prepared by the Intelligence Branch of the U.SArmy Corps of Engineers, in cooperation with the U.S.Geological Survey.Geologic maps and brief descriptions of regions orquadrangles are published in the folios of the U.S.Geological Survey. Generally, the smallest rock unitmapped is a formation; geologic maps indicate theextent of formations by means of letter symbols, color,or symbolic patterns. Letter symbols on the map indicatethe location of sand and gravel pits; sometimes the backof the map sheet has a brief discussion entitled “MineralResources,” that describes the location of constructionmaterials.Ordinary topographic maps may be of some use inestimating soil conditions and can be used inconjunction with geologic maps. Inspection of thedrainage pattern (as indicated by contour lines) canprovide clues as to the nature of rocks, depth ofweathering, soil, and drainage.Agricultural soils maps and reports are availablefor many of the developed agricultural areas of theworld. These studies are usually concerned primarilywith surface soils to a depth of about 6 feet. Informationgiven includes topography, drainage, vegetation,temperature, rainfall, water sources, and rock location.Soils are usually classified according to texture, color,structure, chemical and physical composition, and16-7
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