they are larger than 1/4 inch in diameter). These types of soils are symbolized by using a two-letter designation,
with "G" being the first letter, indicating that the soil is predominantly composed of gravel-sized particles.
Gravels may be further classified based on the amounts of fines associated with the coarse particles.
(a) Gravels Containing Little or No Fine Material. Gravels made up of less than five percent, by
weight, of fine particles (materials with diameters less than the size of the openings in a Number 200 sieve) may
be classified as well-graded or poorly graded.
Well-Graded Gravels. Gravels that contain a relatively uniform distribution of a wide range
of particle sizes are referred to as well-graded gravels or gravel-sand mixtures. Figure 3-5, page 3-13, illustrates
the possible particle size distribution within a well-graded soil. Well-graded soils are symbolized by attaching the
letter "W" to the symbol for the predominant soil type; therefore, the symbol GW signifies a well-graded gravel.
Poorly Graded Gravels. Gravels that do not contain a relatively uniform distribution of a
wide range of particle sizes are said to be poorly graded gravels or gravel-sand mixtures. Figure 3-6, page 3-13
shows the particle -size distributions of two types of poorly graded soils. Poorly graded soils are symbolized by
attaching the letter "P" to the symbol for the predominant soil type; therefore, the symbol GP signifies a poorly
graded gravel.
(b) Gravels Containing Appreciable Amounts of Fine Material. Gravels made up of greater than
12 percent, by weight, of fine particles may be further classified based on the predominate type of fines present.
Silty Gravels. A gravel containing greater than 12 percent, by weight, of fine material, with
silt being the predominant type of fine present, is called a silty gravel or a gravel-sand-silt mixture. Because the
letter "M" is used to represent silts, silty gravels are designated by the symbol GM.
Clayey Gravels. A gravel containing greater than 12 percent, by weight, of fine material,
with clay being the predominant type of fine present, is called a clayey gravel or a gravel-sand-clay mixture.
Because the letter "C" is used to represent clays, clayey gravels are designated by the symbol GC.
(c) Gravels Containing Moderate Amounts of Fine Material. Gravels that contain between 5 and
12 percent, by weight, of fine material are considered to be borderline soil types and are assigned a dual symbol.
For example, such a soil with a well-graded coarse fraction and a fine fraction predominantly composed of silt
would be identified by the symbol GW-GM. Other possible soil types are GW-GC, GP-GM, and GP-GC.
(2) Sands. A coarse-grained soil is classified as a sand if more than half of the coarse fraction, by
weight, consists of particles smaller than the openings in a Number 4 sieve (that is, they are smaller than 1/4 inch
in diameter). These types of soils are symbolized by using a two-letter designation, with "S" being the first letter,
indicating that the soil is predominantly composed of sand-sized particles. Sands may be further classified based
on the amounts of fines associated with the coarse particles.
EN5341
3-10
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