Geology Reference
In-Depth Information
(8) Identification of Organic Fine-Grained Soils:
(8.1) Identify the soil as an organic soil, OL/OH, if the soil contains
enough organic particles to influence the soil properties. Organic
soils usually have a dark brown to black color and may have an
organic odor. Often, organic soils will change color, for example,
black to brown, when exposed to the air. Some organic soils will
lighten in color significantly when air dried. Organic soils normally
will not have a high toughness or plasticity. The thread for the
toughness test will be spongy.
Note 8 —In some cases, through practice and experience, it
may be possible to further identify the organic soils as organic
silts or organic clays, OL or OH. Correlations between the
dilatancy, dry strength, and toughness tests and laboratory
tests can be made to identify organic soils in certain deposits
of similar materials of known geologic origin.
(9) If the soil is estimated to have 15% to 25% sand or gravel, or
both, the words “with sand” or “with gravel” (whichever is more pre-
dominant) shall be added to the group name. For example: “lean
clay with sand, CL” or “silt with gravel, ML” (see Figure 3-2). If
the percentage of sand is equal to the percentage of gravel, use
“with sand.”
(10) If the soil is estimated to have 30% or more sand or gravel, or
both, the words “sandy” or “gravelly” shall be added to the group
name. Add the word “sandy” if there appears to be more sand than
gravel. Add the word “gravelly” if there appears to be more gravel
than sand. For example: “sandy lean clay, CL,” “gravelly fat clay,
CH,” or “sandy silt, ML” (see Figure 3-2). If the percentage of sand
is equal to the percentage of gravel, use “sandy.”
Procedures for Identifying Coarse-Grained Soils
(Contains less than 50% fines)
(1) The soil is a gravel if the percentage of gravel is estimated to be
more than the percentage of sand.
(2) The soil is a sand if the percentage of gravel is estimated to be
equal to or less than the percentage of sand.
(3) The soil is a clean gravel or clean sand if the percentage of fines
is estimated to be 5% or less.
(3.1) Identify the soil as a well-graded gravel, GW, or as a well-
graded sand, SW, if it has a wide range of particle sizes and sub-
stantial amounts of the intermediate particle sizes.
(3.2) Identify the soil as a poorly graded gravel, GP, or as a poorly
graded sand, SP, if it consists predominantly of one size (uniformly
graded), or it has a wide range of sizes with some intermediate sizes
obviously missing (gap or skip graded).
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