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<br />Soll~ <br /> <br />Division SoIl Description ValueAsA DraInage <br />Material Foundation <br /> Wellgrad8ograv8I.orgrav8IiS310mxlur8IitlleQrrfOf'nes Excelle1t Excellent <br /> Poorly graded grave, o'gravelisandmlx:W8S, 1,ltle:)1 1cllnes Good Excellent <br />Gravel ancl Gravelly SoIls <br /> S,lty gra~els, gravelisa1disll: 'l'ixtures Good Poor <br /> C:ayeysands sandiclaymlxtures GQod Poor <br /> 1'Ve1 graded sands or gra~e,lysancs, Wleor nof,ne~ GOOd Excelle1t <br /> Poorlygradedsandso'gravellysa'1ds;lltteornoflnes Fw Excellenl <br />Sand and Sandy SoIls <br /> Slh\/sands,sand'sltmlxlures Fair Fair <br /> Clayey sands sand.':laymlxtures Fair Poo, <br /> Inorganic silts a1d very fine 5ands, rock flour. silty or clayey Fair Poor <br /> fnesancs, or clayey SitS wit'1 sigh: plasticity <br /> 110rganlc SiltS of low to medlu'll p'asticl:y gravelly sands silly Fair ImperviQus <br /> clays. lear clays <br /> Organlcsllticlaysoi owplastlclly Pcm ImoervlOUS <br />SIIt8 and Clays Inorganic sIlts, micaceous or dlatomaceouslin('sand~for Silly sOils <br /> elastic silts Pc:)r Poo, <br /> 110rganlC claysofhgh pastclly, lal clays Very Poor ImpervlOL;S <br /> Organic clays of medll.m tOhlg1 pasticll)' organlcsdls Very Poor ImpervIous <br />Highly Organic Solis Peat ano o:her hlg'1lyorgarlC salls NOISuitable Pc~ <br /> <br />identified by referring to topographic maps and flood- <br />plain technical studies, as well as by conducting detailed <br />site surveys. <br />Site Topography. Identification of topographic ele- <br />ments such as slopes and ground elevations is most im- <br />portant in determining the buildable portion of a site. <br />Topographic data also indicates erosion potential and <br />the need for, and feasibility of, using fill material to en- <br />hance the site for construction. <br />Soil Characteristics. Soil characteristics affect flood <br />damage reduction in several ways. The permeability of <br />soil determines the degree of water absorption, which <br />influences the rate of storm water run-off, erosion, and <br />ground water storage. Soil characteristics also determine <br />the feasibility and design specifications for the use of <br />land fill to elevate buildings, the use of backfill around <br />foundations, and the construction of earth berm levees <br />on the site. Finally, soil analysis will indicate the neces- <br />sary depths for footings and pilings, as well as piers and <br />columns used to elevate buildings. <br />Soil data can often be obtained from the U.S. De- <br />partment of Agriculture's Soil Conservation Service in <br />the form of maps, elevations, tables, and reports, or can <br />be collected by design staff and consultants as part of <br />site-specific surveys. <br />Stability of Slopes. The combination of topography <br />and soil characteristics determines the stability of slopes <br />on the site and affects design decisions in several ways. <br />Slope stability affects the choice of the actual building <br />site, the use of fill material, and the design of founda- <br /> <br />Soil characteristics must he <br />analyzed to determine the <br />soil's drainage characteris- <br />tics and its value as foun- <br />dation material <br /> <br />47 <br />