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FINE-GRAINED SOILS - 14070_389
FIELD IDENTIFICATION - 14070_391

Engineering Aid 1 - Advanced Structural engineering guide book
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Figure  16-4.—Grain  size  distribution  chart. You should plot these values on a form like the one shown  in  figure  16-4.  The  graph  on  this  form  is  a logarithm  type  of  layout;  coordinates  horizontally  are sieve sizes (at the top) and grain sizes in millimeters (at the  bottom).  Vertical  coordinates  are  percents  passing. The formula for determining D60 means  the  grain  size,  in  millimeters,  indicated by the gradation curve at the 60-percent passing level. In figure 16-4, follow the 60-percent passing line to the point  where  it  intersects  the  gradation  curve  for FT-P1-1; then drop down and read the grain size in millimeters indicated below. You read about 1.25mm. D10 means, similarly, the grain size indicated by the gradation curve at the 10-percent passing level. In figure 16-4,  this  is  about  0.11mm. for this sample, then, is 1.25/0.11, or about 11.4. COEFFICIENT OF CURVATURE f  o  r The i s    a s    f o l l o w s : is   as   follows: means the coefficient of curvature  of the gradation   curve.   Sometimes   the   symbol coefficient of gradation)  is used instead of formula  for  determining D30 is the grain size, in millimeters, indicated by the gradation curve at the 30-percent passing level. In figure 16-4, it is (for FT-P1-1) about 0.35. Therefore, 0.352 divided by (0.11 x 1.25), or about 0.89. FT-P1-1 is obviously a sand, since more than half of its coarse fraction passes the No. 4 sieve. It is a clean sand, since less than 5 percent of it (see table AV-1, appendix V) passes the No. 200 sieve. However, it is not a well-graded sand (SW), because although its greater than 6 (prescribed for SW in appendix V), its is  less  than  1,  the  minimum  prescribed  for  SW. is is 16-14







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