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Classification uses the following symbols: Basic Symbols Modifying Symbols G - gravel W -well graded S - sand P - poorly graded M -with silt fines C - with clay fines The following are basic facts about coarse-grained soil classification: ' • The basic symbol G is used if the estimated percentage of gravel is greater than that for sand. In contrast, the symbol S is used when the estimated percentage of sand is greater than the percentage of gravel. ' • Gravels range in size from 3-inch to 0.25-inch (No. 4 sieve). Sands range in size from No. 4 sieve to No. 200 sieve. Use the grain size scale used by engineers (ASTM Standards D422- 63 and D643-78) to further classify grain size as specified by the USCS. Note: This grain size scale differs from the Modified Wentworth Scale used in teaching most geologists. Also, it introduces a distinction between sorting and grading. ' • The modifying symbol W indicates good representation of all particle sizes. ' • The modifying symbol P indicates that there is a predominant excess or absence of particle sizes. • The symbol W or P is only used when there is less than 15 percent fines in a sample. • Modifying symbol M is used if fines have little or no plasticity (silty). • Modifying symbol C is used if fines have low to high plasticity (clayey). ' • The following rules apply for the written description of the soil group name: Types of Soil Rule Sands and gravels (clean) Less than 5 percent fines Sands (or gravels)with fines 5 to 15 percent fines Silty (or clayey) sands or gravels Greater than 15 percent fines ' Other descriptive information includes: Color ' Maximum grain size Composition of grains Approximate percentage of gravel, sand, and fines (use a percentage estimation chart) ' Modifiers Description Trace Less than 5 percent ' Few 5 to 10 percent Little 15 to 25 percent Some 30 to 45 percent ' Mostly 50 to 100 percent Mineralogy Soil Investigation Work Plan, Stockton Railyard 3 giadminassA(obs120031032777.16_union pacific-stockton yartA09-reports19.09_reportslwork plan_soilboringlappendiceslapp_b_boreholelogging.doc