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Classification of Soils for Engineering Purposes <br />ASTM Designation D-2487 and D 2488 (Unified Soil Classification System) <br />Major Divisions Group Typical Names Classification Criteria <br />Symbols <br />Course Grained Soils <br />More than 50% retained on No. 200 sieve " <br />Gravels <br />50% or more of coarse fraction <br />retained on No. 4 sieve. <br />Clean Gravels <br />Well —graded gravels <br />and gravel -sand <br />GW mixtures, little or no <br />fines. <br />Classification on basis of percentage of fines. <br />Less than 5% passing No. 200 Sieve: GW, GP, SW, SP <br />More than 12% passing No. 200 Sieve: GM, GC, SM, SC <br />From 5% to 12% passing No. 200 Sieve: Borderline Classification <br />requiring use of duel symbols. <br />Cu = D60 / D10 greater than 4. <br />Cz = (D30)2 / (D10 x D60) between 1 & 3. <br />Poorly graded gravels <br />GP and gravel -sand <br />mixtures, little or no <br />fines. <br />Not meeting both criteria for GW materials. <br />Gravels with <br />Fines <br />Silt gravels, ravel- <br />GM y 9 <br />sand -silt mixtures. <br />Atterberg limits <br />below "A" line, or Atterberg limits plotting <br />P.I. less than 4. in hatched area are <br />GC Clayey gravels, gravel- <br />sand -clay mixtures. <br />borderline <br />Atterberg limits classifications requiring <br />above "A" line with q g <br />use of dual symbols. <br />P.I. greater than 7. <br />Cu = D60 / D10 greater than 6. <br />2 <br />Cz = (D30) / (D10 x D60) between 1 & 3. <br />Sands <br />More than 50% of coarse <br />fraction passes No 4 sieve. <br />Clean Sands <br />Well -graded sands and <br />SW gravelly sands, little or <br />no fines. <br />Poorly -graded sands <br />SP and gravelly sands, little <br />or no fines. <br />Not meeting both criteria for SW materials. <br />Sands with <br />Fines <br />SM Silty sands, sand -silt <br />mixtures. <br />Atterberg limits <br />below "A" line, or Atterberg limits plotting <br />P.I. less than 4. in hatched area are <br />Clayey sands, sand- <br />SC clay mixtures. <br />Atterberg limits borderline <br />above "A" line with classifications requiring <br />use of dual symbols. <br />P.I. greater than 7. <br />Fine Grained Soils <br />More than 50% passes No. 200 sieve " <br />Silts and Clays <br />Liquid Limit of 50% or <br />less <br />Inorganic silts, very fine <br />ML sands, rock flour, silty <br />or clayey fine sands. <br />Plasticity Index Chart <br />60 <br />Inorganic days of low to <br />medium plasticity, <br />CL gravelly clays, sandy <br />clays, silty days, lean <br />clays. <br />50 <br />Ana,r�oo�a�r�oa�oo«�e9,a�edm��s <br />CHSoils <br />.. 40 <br />Atterbe <br />eo,„1,.eo�a����oa�os,e4w�9seo�da� <br />g mltsplo <br />tinglnna oneda,eaa,e <br />•C <br />E <br />Tymbols. <br />Organic silts and <br />OL organic silty clays of <br />low plasticity. <br />30 <br />:,,' <br />m <br />I CL soils I <br />n° uoe <br />Silts and Clays <br />Liquid Limit greater than <br />50%. <br />Inorganic silts, <br />micaceous or <br />MH diatomaceous fine <br />sands or silts, elastic <br />silts. <br />a 20 <br />10 <br />I OH & M HSoils <br />CH Inorganic clays of high <br />plasticity, fat clays. <br />CL- <br />L Soils <br />I OL8 ML Soils <br />0 <br />0 10 <br />20 <br />30 40 50 <br />Liquid <br />60 <br />Limit <br />70 <br />80 <br />90 <br />100 <br />Organic clays of <br />OH medium to high <br />plasticity. <br />c <br />p, O, C <br />20tH <br />Peat, muck and other <br />Pt highly organic soils. <br />12 <br />