The plasticity chart plots

Ip on vertical axis against wL on horizontal axis

wL vertical against Ip horizontal

The A-line, Ip = 0.73(wL-20), separates

clays above from silts and organic soils below

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Draw plasticity chart with symbols

Short answer

Plasticity chart plots Ip against wL with A-line Ip=0.73(wL-20), U-line, and vertical lines at 35% and 50%. Above A-line are clays CL, CI, CH; below are silts/organics ML, MI, MH; hatched zone gives CL-ML.

Draw neatly the plasticity chart (IS / USCS) and label the group symbols of the various soil regions in the chart.

The plasticity chart (Casagrande) plots plasticity index $I_p$ (vertical) against liquid limit $w_L$ (horizontal). It is used for the fine-grained fraction (passing 75 micron).

Lines

A-line: $I_p = 0.73(w_L - 20)$ , separating clays (above) from silts and organic soils (below).
U-line: $I_p = 0.9(w_L - 8)$ , the upper limit for natural soils.
A vertical line at $w_L = 50\%$ (USCS) separates low and high plasticity. IS adds a line at $w_L = 35\%$ , giving low (L), intermediate (I) and high (H) plasticity.

  Ip (%)
  50 |              |     |    : U-line  /
  45 |              |     |  :         / A-line
  40 |              |     |:   CH   /
  35 |              |    :|      /
  30 |              |  :  |   /
  25 |              :     | /
  20 |            : |CI  /|
  15 |          :   | /   |  MH or OH
  10 |        : CL /|     |
   7 |      :-----/ | MI  |  <- CL-ML band (Ip 4 to 7)
   4 |     :----/   | OI  |
   0 |   :    / ML  |     |  (ML or OL below A-line)
     +------------------------------------ wL (%)
      0       20    35    50      70

(/ = A-line, : = U-line, | = vertical lines at $w_L$ = 35% and 50%; the vertical scale is not uniform near the bottom.)

Group symbols

Region	Symbol	Name
Above A-line, $w_L < 35$ (IS) / 50 (USCS)	CL	Inorganic clay of low plasticity
Above A-line, $35 < w_L < 50$ (IS)	CI	Inorganic clay of intermediate plasticity
Above A-line, $w_L > 50$	CH	Inorganic clay of high plasticity
Below A-line, $w_L < 35$ / 50	ML (OL)	Inorganic silt (organic silt) of low plasticity
Below A-line, $35 < w_L < 50$	MI (OI)	Inorganic silt (organic soil) of intermediate plasticity
Below A-line, $w_L > 50$	MH (OH)	Inorganic silt of high plasticity (organic clay)
Hatched zone, $I_p$ 4 - 7 above A-line	CL-ML	Silty clay

✓ Answer checked by Claude Opus 5.5 (high effort)

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Draw plasticity chart with symbols

Lines

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