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Figure 15-35.-Liquid limit test.
Figure  15-37.-Data  sheet,  Atterberg  limits  determination.

Engineering Aid 3 - Beginning Structural engineering guide book
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Figure 15-36.-Removing sample portion for moisture content. the  groove  (fig.  15-36).  Place  this  in  a  mois- ture   content   can,   weigh   it,   and   record   the weight.   Oven-dry   and   record   the   difference in  weights.  This  is  the  weight  of  the  water content. 4.  Transfer  the  remaining  soil  in  the  cup  to the evaporation dish. Wash and dry the cup and grooving tool. Reattach the cup in preparation for the next run. 5. Run at least five tests on each soil, with two closures  above,  two  closures  below,  and  one closure  at  or  near  the  25-blow  line.  An  ideal spread is closures at 16, 23.5, 29, and 33 blows. If each testis perfect, the plotted line through all points is shown as a straight line. If some tests are imperfect, the operator can usually get good results by using the three plotted points lying most nearly in a straight line. To  determine  the  liquid  limit,  plot  a  FLOW CURVE on a graph like the one shown in figure 15-37.  It  is  a  semilogarithmic  graph,  in  which  the vertical  coordinates  are  water  content  and  the horizontal coordinates are number of blows. The flow curve is a straight line plotted as nearly as possible  through  three  or  more  of  the  plotted points. In figure 15-37, the first-run sample was tested three times for an average number of 16 hammer blows.  The  water  content  was  47.3  percent.  On the graph, 16 and 47.3 are the coordinates of one of  the  three  Xs  shown  plotted.  The  second-run sample  indicated  24  hammer  blows  and  46.6 percent water content; these are the coordinates of  another  of  the  Xs  plotted  to  the  right.  Coor- dinates for the third X are the hammer blows and water content for the third-run sample. The coor- dinates of the rest of the plotted points are as in- dicated by the hammer blows and water content for the succeeding runs. The plotted points in the graph may not form a straight line; however, the liquid limit line (or flow curve) is a straight line, passing  nearly  through  the  mean  of  the  plotted points (fig. 15-37). The usual recommendation is that five or six trials be made so that the results are more representative. The liquid limit (LL) is the water content for 25 blows; it is therefore indicated by the point of intersection between the flow curve and the ver- tical line representing 25 blows. The water con- tent indicated is about 46.4 percent. This, when rounded  off  to  46,  is  the  liquid  limit. The plastic limit of soil is the lowest water con- tent at which the soil just begins to crumble when rolled into threads 1/8 in. in diameter, at slowly decreasing   water   content.   First,   prepare   the sample  as  follows: If   you   need   only   the   plastic   limit,   take a  quantity  of  soil  weighing  about  15  g  from the  prepared  material  in  the  evaporating  dish. Place   this   air-dried   soil   in   an   evaporating 15-32







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