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STANDARD 18-1 sification. Example: A gravel with 10 percent fines, a C„ of 20, a q of 2.0, and a plasticity index of 6 would be classified as GW -GM rather than GW -GC.) . . SECTION 18.107 — PROCEDURE FOR CLASSIFICATION OF FINE-GRAINED SOILS (50 PERCENT OR MORE PASSING) From the material passing the 3 -inch (76 mm) sieve, select a test sample for the determination of the liquid limit and plasticity in- dex. The method for wet preparation shall he used for soils con- taining organic matter or irreversible mineral colloids. Determine the liquid limit and the plasticity index of a portion of the test sample passing the No. 40 (425 p.m) sieve. Classify the soil as inorganic clay, C, if the plot of liquid limit versus plasticity index falls above the "A" line and the plasticity index is greater than 7. Classify the soil as inorganic clay of low to medium plasticity, CL, if the liquid limit is less than 50 and the plot of liquid limit ver- sus plasticity index falls above the "A" line and the plasticity in- dex is greater than 7. See area identified as CL on the Plasticity Chart of Table 18-1-A. Classify the soil as inorganic clay of high plasticity, CH, if the liquid limit is greater than 50 and the plot of liquid limit versus plasticity index falls above the "A" line. In cases where the liquid limit exceeds 100 or the plasticity index exceeds 60, the plasticity chart may be expanded by maintaining the same scales on both axes and extending the "A" line at the indicated slope. See areas identified as CH on the Plasticity Chart, Table 18-1-A. Classify the soil as inorganic silt, M, if the plot of liquid limit versus plasticity index falls below the "A" line or if the plasticity index is less than 4, unless it is suspected that organic matter is 1997 UNIFORM BUILDING CODE present in sufficient amounts to influence the soil properties, then tentatively classify the soil as organic silt or clay, O. If the soil has a dark color and an organic odor when moist and warm, a second liquid limit test should be performed on a test sam- ple which has been oven dried at 110°C -t 5°C for 24 hours. Classify the soil as organic silt or clay, O, if the liquid limit after oven drying is less than three fourths of the liquid limit of the origi- nal sample determined before drying. Classify the soil as inorganic silt of low plasticity, ML, or as or- ganic silt of low plasticity, ML, or as organic silt or silt -clay of low plasticity, OL, if the liquid limit is less than 50 and the plot of liq- uid limit versus plasticity index falls below the "A" line or the plasticity index is less than 4. See area identified as ML and OL on the Plasticity Chart, Table 18-1-A. Classify the soil as inorganic silt of medium to high plasticity, MH, or as organic clay or silt -clay of medium to high plasticity, OH, if the liquid limit is more than 50 and the plot of liquid limit versus plasticity index falls below the "A" line. See area identified as MH and OH on the Plasticity Chart of Table 18-1-A. In order to indicate their borderline characteristics, some fine-grained soils should be classified by dual symbols. If the plot of liquid limit versus plasticity index falls on or prac- tically on the "A" line or above the "A" line where the plasticity index is in the range of 4 to 7, the soil should be given an appropri- ate borderline classification such as CL -ML or CH -OH. If the plot of liquid limit versus plasticity index falls on or prac- tically on the line liquid limit = 50, the soil should be given an ap- propriate borderline classification such as CL -CH or ML -MH. (In doubtful cases the rule for classification is to favor the more: plas- tic classification. Example: a fine-grained soil with a liquid limit of 50 and a plasticity index of 22 would be classified as CH -MH rather than CL ML.) TABLE 18-1 -A—SOIL CLASSIFICATION CHART !Based on the material passing the 3 -inch (76 mm) sieve. 3-328 .MAJOR DiVtSIONS GROUP SYMBOLS TYPICAL NAMES CLEAN GW Well -graded gravels and gravel -sand mixtures, little or no fines GRAVELS GRAVELS GP Poorly graded gravels and gravel -sand mixtures, little or no fines COARSE- GRAINED SOILS 50% or mora of coarse fraction retained on No.4 (4,75 min) sieve - GRAVELS FINES WITHGC GM Silty gravels, gravel -sand -silt mixtures Clayey gravels, -gravel -sand -lay mixtuies . More than 50% retafried on No. re.200 SANDS More than 50% of coarse.fraction pass" No.4 (4.75 mm) Steve CLEAR SANDS SW Well graded sands and gravelly sands, little or no lines SP Poorly graded sands and gravelly and sands, little or no fines SANDS SM Silty sands, sand -sill mixtures wlnl FINES ..Sc.Clayey sands, sandclay mixtures ML Inorganic silts, very fine sands, rock flour, sillyoi clayey fine sands - - FINE-GRAINED SOILS SILTS AND CLAYS . Liquid Umft 50% or llss CL Inorganic blays of low to medium plasticity, gravell t IAyS, sandy _ clays, silty clays, lean clays 50%'ix Mors passe: OL Organic silts and organic silty clays of low plasticity :i, SILTS AND CLAYS Liquid Ilmit greater than 50% 0! hfflNe Inorganic sills, micaceous or diatomaceous fine sands or silts, elastic silts CH Inorganic clays of high plasticity, fat clays OH Organic clays of medium to high plasticity Highly organic Sdia PT Peat, muck and other highly organic soils !Based on the material passing the 3 -inch (76 mm) sieve. 3-328