Figure 15-58.—Soil profile.Soil ClassificationThe soils you normally work with in earthworkoperations are classified as follows:. Coarse grained. Fine grainedl OrganicCOARSE-GRAINED SOILS.— Soils in thisclassification are composed of sand and gravel and arein the B-horizon. Coarse-grained soils have 50 percentor less material passing the No. 200 sieve. Their grainshape varies from rounded to angular and has goodload-bearing qualities and drains freely.FINE-GRAINED SOILS.— Fine-grained soilsare composed of silt and clay and are in the B-horizon.They have 50 percent or more material passing the No.200 sieve. Fine-grained soils have good-load bearingqualities when dry; however, these soils drain poorly,and when wet, have little or no load-bearing strength.This characteristic is especially true with clay.ORGANIC SOILS.— Organic soils, sometimesreferred as top soil, are composed mostly of decayedplant and animal matter and are in the A-horizon.These soils retain moisture, are difficult to compact,and are normally used when landscaping a finishproject.Soil SizesSoils are grouped by the size of their particlegrains. One method used to distinguish sizes isthrough the use of sieves (fig. 15-59). A sieve is ascreen attached across the end of a cylindrical metalframe. The screen allows particles smaller than itsopenings to fall through and retains larger particles.Sieves with screen openings of different sizes allowsyou to sort soil into particle groups, based on size.Sieve sizes are designated by the screen openingsize; for example, a 3-inch sieve has a screen withopenings 3 inches square. A No. 4 sieve has fouropenings per linear inch, thus having 16 openings persquare inch.Figure 15-59.—Standard sieve set.15-35
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