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<br />STANDARD 18-1
<br />
<br />sification. Example: A gravel with 10 percent fines, a Cu of 20, a
<br />Cz of 2.0, and a plasticity index of 6 would be classified as
<br />GW-GM rather than GW-Gc.)
<br />
<br />SECTION 18.107 - PROCEDURE FOR
<br />CLASSIFICATION OF FINE-GRAlNED SOilS
<br />(50 PERCENT OR MORE PASSING)
<br />
<br />From the material passing the 3-inch (76 mm) sieve, select a test
<br />sample for the determination of the liquid limit and plasticity in-
<br />dex. The method for wet preparation shall be used for soils con-
<br />taining organic matter or irreversible mineral colloids.
<br />
<br />Determine the liquid limit and the plasticity index of a portion
<br />of the test sample passing the No. 40 (425 f.lm) sieve.
<br />
<br />Classify the soil as inorganic clay, C, if the plot of liquid limit
<br />versus plasticity index falls above the " A" line and the plasticity
<br />index is greater than 7.
<br />
<br />Oassify the soil as inorganic clay of low to medium plasticity,
<br />CL, if the liquid limit is less than 50 and the plot of liquid limit ver-
<br />sus plasticity index falls above the" A" line and the plasticity in-
<br />dex is greater than 7. See area identified as CL on the Plasticity
<br />Chart of Table 18-1-A
<br />
<br />Oassify the soil as inorganic clay of high plasticity, CH, if the
<br />liquid limit is greater than 50 and the plot of liquid limit versus
<br />plasticity index falls above the "A" line. In cases where the liquid
<br />limit exceeds 100 or the plasticity index exceeds 60, the plasticity
<br />chart may be expanded by maintaining the same scales on both
<br />axes and extending the c'A" line at the indicated slope. See areas
<br />identified as CH on the Plasticity Chart, Table 18-I-A.
<br />
<br />Oassify the soil as inorganic silt, M, if the plot of liquid limit
<br />versus plasticity index falls below the" A " line or if the plasticity
<br />index is less than 4, unless it is suspected that organic matter is
<br />
<br />1997 UNIFORM BUILDING CODE
<br />
<br />present in sufficient amounts to influence the soil properties, then
<br />tentatively classify the soil as organic silt or clay, O.
<br />
<br />If the soil has a dark color and an organic odor when moist and
<br />warm, a second liquid limit test should be performed on a test sam-
<br />ple which has been oven dried at 1l0oC :t 50C for 24 hours.
<br />
<br />Oassify the soil as organic silt or clay, 0, if the liquid limit after
<br />oven drying is less than three fourths of the liquid limit of the origi-
<br />nal sample determined before drying.
<br />
<br />Classify the soil as inorganic silt of low plasticity, ML, or as or-
<br />ganic silt of low plasticity, ML, or as organic silt or silt-clay of low
<br />plasticity, OJ..., if the liquid limit is less than 50 and the plot of liq-
<br />uid limit versus plasticity index faUs below the "An line or the
<br />plasticity index is less than 4. See area identified as ML and OL on
<br />the Plasticity Chart, Table I8-I-A.
<br />
<br />Classify the soil as inorganic silt of medium to high plasticity,
<br />MH, or as organic clay or silt-clay of medium to high plasticity,
<br />OR, if the liquid limit is more than 50 and the plot of liquid limit
<br />. versus plasticity index falls below the "An line. See atea identified
<br />as MH and OH on the Plasticity Chart of Table 18-I-A.
<br />
<br />In order to indicate their borderline characteristics, some
<br />fine-grained soils should be classified by dual symbols.
<br />
<br />If the plot of liquid limit versus plasticity index falls on or prac-
<br />tically on the "A" line or above the" A" line where the plasticity
<br />index is in the range of 4 to 7, the soil should be given an appropri-
<br />ate borderline classification such as CL-ML or CH-OH.
<br />
<br />If the plot of liquid limit versus plasticity index falls on or prac-
<br />tically on the line liquid limit = 50, the soil should be given an ap-
<br />propriate borderline classification such as CL-CH or ML-MH. (In
<br />doubtful cases the rule for classification is to favor the more. phis-
<br />tic classification. Example: a fine-grained soil with a liquid limit
<br />of 50 and a plasticity index of 22 would be classified as CH-MH
<br />rather than CL-ML.)
<br />
<br />~~)
<br />
<br />t
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<br />
<br />TABLE 18-1-A-SOIL CLASSIACATION CHART
<br />
<br />1 Based on the material passing the 3-inch (76 mm) sieve.
<br />
<br />3-328
<br />
<br /> GROUP
<br /> .MAJOR DIVISIONS SYMBOLS TYPICAL NAMES
<br /> ClEAN GW Well-graded gravels and gravel-sand mixtures, little or no fines
<br /> GRAVELS GRAVELS GP Poorly graded gravels and gravel-sand mixtures. little or no fines
<br /> 50% or II10AI of coarse fraction GM Silty gravels, gravel-sand-silt mixtures
<br />COARSE- retained on No. 4 (4.75 min) sieve GRAVELS
<br />GRAINED WITH RNES ~OC aayey gravels,: gravel-sand~ay mixtures :j
<br />SOILS ..._-
<br />More'than 50% ClEAN SW! Well.;.graded sands arid gravelly sands, little or no fiDes .,)
<br />retained on No. 200 SANDS SP Poorly graded sands and gravelly and sands, little or no fines
<br />(75 fdI') sieve" SANDS
<br /> More than 50% of coarsdraction SM Silty sands, sand-silt mixtures : . .
<br /> passes No.4 (4.75 mm) sieYe SANDS
<br /> WITH ANES "SC 'Oayey sands, sand.:.clay mixtures : .'.\ :
<br />i ML Inorganic silts, 'Very fine sands, rock flour, silt yoi' clayey fine
<br /> sands -
<br /> SILTS AND ClAYS Inorganic clays of low to medium plasticity, gravelly clays, sandy
<br /> . liquid Umit SO% or less CL,
<br />ANE-GRAlNED SOILS clays, silty clays, lean clays
<br />50%0, more ~ OL Organic silts and organic silty clays of low plasticity
<br />~ 200 ~ fAIl') In~)lganic silts, micaceous or diatomaceous fme sands or silts,
<br />sieve 1 MH'
<br /> SILTS AND CLAYS ' ' elastic silts
<br /> Uquld limit greater than SO% CH Inorganic clays of high plasticity, fat clays
<br /> OH Organic clays of medium to high plasticity
<br /> Highly Organic Solis PT Peat, muck and other highly organic soils
<br />
<br />(~~
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