Therefore, it is in the SP (poorly graded sands, gravelly sands, little or no fines) category. SAMPLE  CLASSIFICATION  PROBLEMS shows a The  following  soil  classification  problems  are presented to show you how the soil classification chart (table AV-1, appendix V) is used to classify soils. Sample Problem 1. From a sieve analysis, a soil of 20 and a gravel, 88-percent sand, and no fines (smaller than No. 200).  When  you  are  classifying  this  soil,  the  first question  is  whether  the  soil  is  coarse-grained  or fine-grained. To be Coarse-grained, a soil must have less than  50-percent  fines.  This  soil  contains  no  fines; therefore, it is a coerse-grained soil with the first letter in the symbol either G (gravel) or S (sand). Since it contains  more  sand  (88  percent)  than  gravel  (12 percent), the first letter in the symbol must be S. The next task is to determine the second letter in the symbol.  Since  the  soil  contains  no  fines,  it  has  no plasticity characteristics; therefore, the second letter of the symbol must be either W (well graded) or P (poorly graded). Since the soil has a Cu greater than 6 and a C_c between  1  and  3,  it  must  be  well-graded.  Therefore,  the symbol for the soil is SW, meaning “well-graded sand.” Sample Problem 2. A sieve analysis shows that a soil  contains  (50-Percent  gravel,  20-percent  sand,  and 20-percent fines. Plasticity tests show that the portion passing the No. 40 sieve has an LL of 35 and a PI of 8. Since the soil contains less than 50-percent fines, it is a coarse-grained soil. The first letter is therefore either G (gravel) or S (sand). Since gravel predominates over sand, the first letter is G. The next questions are (1) does the soil contain less than  12-percent  fines  and  (2)  is  it  nonplastic?  The answer to both questions is negative, since the sieve analysis shows 20-percent fines, and an LL and PI have been  obtained.  It  follows  that  the  second  letter  in  the symbol must be either C (clay) or M (silt). If you plot LL 35 and PI 8 on the plasticity chart (fig. 16-3), you will find that the plotted point lies below the A-line. Therefore,  the  complete  symbol  is  GM,  meaning  “silty gravel.” Sample Problem 3. A sieve analysis shows that a soil  contains  10-percent  sand  and  75-percent  fines. Plasticity tests show that the portion passing the No. 40 sieve has an LL of 40 and a PI of 20. Since the soil contains  more  than  50-percent  fines,  it  is  a  fine-grained soil; therefore, the first letter in the symbol is either O (organic), M (silt), or C (clay). Assume that the soil shows   no   indication   of   being   organic   (principal indications  are  black  color  and  musty  odor);  it  follows that the first letter must be either M or C. If you plot an LL of 40 and a PI of 20 on the plasticity chart, you find that the plotted point lies above the A-line; therefore, the first letter in the symbol is C. Since the liquid limit is less than 50 (which brings the plotted point to the left of the B-line), the second letter of the symbol  is  L  (low  plasticity  or  compressibility).  The complete  symbol  is  CL,  meaning  “clay  with  low compressibility.” of  1.3  and  contains  12-percent FIELD IDENTIFICATION Sometimes the lack of time and facilities makes laboratory  soil  testing  impossible  in  military construction. Even when laboratory tests are to follow, field identification tests must be made during the soil exploration. Soil types need to be identified so that duplicate  samples  for  laboratory  testing  are  held  to  a minimum.  Several  simple  tests  used  in  field identification are described in this section. Each test may  be  performed  with  a  minimum  of  time  and equipment. However, the classification derived from these  tests  should  be  considered  an  approximation.  The number of tests used depends on the type of soil and the experience of the individual using them. Experience is the  greatest  asset  in  field  identification;  learning  the technique from an experienced technician is the best method  of  acquiring  the  skill.  If  assistance  is  not available, you can gain experience by getting the “feel” of  the  soil  during  laboratory  testing.  An  approximate identification can be made by spreading a dry sample on a flat surface and examining it. All lumps should be pulverized until individual grains are exposed but not broken;  breaking  changes  the  grain  size  and  the character  of  the  soil.  A  rubber-faced  or  wooden  pestle are  recommended.  For  an  approximate  identification, however, you can mash a sample underfoot on a smooth surface. Field  tests  may  be  performed  with  little  or  no equipment other than a small amount of water. However, accuracy and uniformity of results is greatly increased by the proper use of certain items of equipment. For testing  purposes,  the  following  equipment  or accessories may be used: . SIEVES. A No. 40 U.S. standard sieve is perhaps the most useful item of equipment. Any screen with about 40 openings per lineal inch could be used. An approximate separation may be made by sorting the 16-15