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Soils
Soil  Gradation

Equipment Operator Basic - Beginning construction equipment operators manual
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Figure 15-58.—Soil profile. Soil Classification The soils you normally work with in earthwork operations  are  classified  as  follows: . Coarse grained . Fine grained l  Organic COARSE-GRAINED  SOILS.—  Soils  in  this classification are composed of sand and gravel and are in the B-horizon. Coarse-grained soils have 50 percent or less material passing the No. 200 sieve. Their grain shape varies from rounded to angular and has good load-bearing  qualities  and  drains  freely. FINE-GRAINED  SOILS.—  Fine-grained  soils are 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 bearing qualities  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, sometimes referred  as  top soil, are  composed  mostly  of  decayed plant and animal matter and are in the A-horizon. These soils retain moisture, are difficult to compact, and  are  normally  used  when  landscaping  a  finish project. Soil Sizes Soils  are  grouped  by  the  size  of  their  particle grains.  One  method  used  to  distinguish  sizes  is through  the  use  of  sieves  (fig.  15-59).  A  sieve  is  a screen attached across the end of a cylindrical metal frame. The screen allows particles smaller than its openings  to  fall  through  and  retains  larger  particles. Sieves with screen openings of different sizes allows you  to  sort  soil  into  particle  groups,  based  on  size. Sieve sizes are designated by the screen opening size; for example, a 3-inch sieve has a screen with openings  3  inches  square.  A  No.  4  sieve  has  four openings per linear inch, thus having 16 openings per square inch. Figure  15-59.—Standard  sieve  set. 15-35







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