material and the letter "L" refers to low plasticity; therefore, the symbol ML is used to represent a silt with low
plasticity.
(b) Clays With Low Plasticity. With the exception of one small area, fine-grained, inorganic soils
that plot to the left of the vertical line representing a LL of 50 and above the "A" line on ENG Form 4334 are
referred to as clays with low plasticity, or lean clays. As mentioned previously, the letter "C" indicates clay-sized
material and the letter "L" refers to low plasticity; therefore, the symbol CL is used to represent a clay with low
plasticity.
(c) Low Plasticity Clay/Silt Mixtures. Soils that plot above the "A" line on ENG Form 4334 and
have LLs ranging from 10 to 30 and PIs ranging from 4 to 7 are called low plasticity clay/silt mixtures. These
types of soils are represented by the symbol CL-ML, indicating that they are low plasticity soils comprised of a
mixture of clay- and silt-sized particles.
(d) Organics With Low Plasticity. Fine-grained, organic soils that plot to the left of the vertical line
representing a LL of 50 and below the "A" line on ENG Form 4334 are referred to as organics with low plasticity.
The letter "O" is used to indicate organic material; therefore, the symbol OL refers to organic material with low
plasticity.
(2) Liquid Limit Greater Than 50. Soils that have a LL greater than 50 (those that plot to the right of
the vertical line representing a LL of 50 on ENG Form 4334) are said to have high plasticity. These types of soils
are symbolized by using a two-letter designation, with the second letter being an "H," indicating that the soils
exhibit high plasticity. Soils with high plasticity may be further classified based on their plotted positions relative
to the "A" line on ENG Form 4334.
(a) Silts With High Plasticity. Fine-grained, inorganic soils that plot to the right of the vertical line
representing a LL of 50 and below the "A" line on ENG Form 4334 are referred to as silts with high plasticity.
Loess is a good example of this type of soil. As mentioned previously, the letter "M" indicates silt-sized material
and the letter "H" refers to high plasticity; therefore, the symbol MH is used to represent a silt with high
plasticity.
(b) Clays With High Plasticity. Fine-grained, inorganic soils that plot to the right of the vertical
line representing a LL of 50 and above the "A" line on ENG Form 4334 are referred to as clays with high
plasticity, or fat clays. The gumbo clays of the southern United States are good examples of this type of material.
As mentioned previously, the letter "C" indicates clay-sized material and the letter "H" refers to high plasticity;
therefore, the symbol CH is used to represent a clay with high plasticity.
(c) Organics With High Plasticity. Fine-grained, organic soils that plot to the right of the vertical
line representing a LL of 50 and below the '"A" line on ENG Form 4334 are referred to as organics with high
plasticity. As mentioned, the letter "O" is used to indicate organic material; therefore, the symbol OH refers to
organic material with high plasticity.
(3) Highly Organic Soils. If the color, odor, or fibrous texture of a fine-grained soil indicates that it is
composed largely of organic material, the soil is termed peat. These types of soils commonly contain particles of
leaves, grass, branches, or other fibrous vegetable material. The symbol for peat is the two-letter designation, Pt.
3-15
EN5341
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