Classification of Soils for Engineering Purposes - Soil Properties: Testing, Measurement, and Evaluation - page 150

Table 11-2 Descriptions of AASHTO Classification Groups [1]
(1) Granular Materials . Containing 35% or less passing 0.075 mm (No. 200) sieve, Note 1.
(1.1) Group A-1: The typical material of this group is a well-graded mixture of
stone fragments or gravel, coarse sand, fine sand and a nonplastic or feebly
plastic soil binder. However, this group includes also stone fragments, gravel,
coarse sand, volcanic cinders, etc. without soil binder.
(1.1.1) Subgroup A-1-a includes those materials consisting predominantly of
stone fragments or gravel, either with or without a well-graded
binder of fine material.
(1.1.2) Subgroup A-1-b includes those materials consisting predominantly of
coarse sand either with or without a well-graded soil binder.
(1.2) Group A-3: The typical material of this group is fine beach sand or fine desert
blow sand without silty or clay fines or with a very small amount of nonplas-
tic silt. The group includes also stream-deposited mixtures of poorly-graded
fine sand and limited amounts of coarse sand and gravel.
(1.3) Group A-2: This group includes a wide variety of “granular” materials which
are borderline between the materials falling in Groups A-1 and A-3 and silt-
clay materials of Groups A-4, A-5, A-6, and A-7. It includes all materials con-
taining 35% or less passing the 0.075-mm sieve which cannot be classified as
A-1 or A-3, due to fines content or plasticity or both, in excess of the limita-
tions for those groups.
(1.3.1) Subgroups A-2-4 and A-2-5 include various granular materials con-
taining 35% or less passing the 0.075-mm sieve and with a minus
0.425 mm (No. 40) portion having the characteristics of the A-4 and
A-5 groups. These groups include such materials as gravel and coarse
sand with silt contents or plasticity indexes in excess of the limita-
tions of Group A-1, and fine sand with nonplastic silt content in
excess of the limitations of Group A-3.
(1.3.2) Subgroups A-2-6 and A-2-7 include materials similar to those described
under Subgroups A-2-4 and A-2-5 except that the fine portion contains
plastic clay having the characteristics of the A-6 or A-7 group.
Note 1: Classification of materials in the various groups applies only to the fraction
passing the 75-mm sieve. Therefore, any specification regarding the use of A-1,
A-2, or A-3 materials in construction should state whether boulders (retained
on 3-in. sieve) are permitted.
(2) Silt-Clay Materials . Containing more than 35% passing the 0.075-mm sieve.
(2.1) Group A-4: The typical material of this group is a nonplastic or moderately
plastic silty soil usually having the 75% or more passing the 0.075-mm sieve.
The group includes also mixtures of fine silty soil and up to 64% of sand and
gravel retained on 0.075-mm sieve.
(2.2) Group A-5: The typical material of this group is similar to that described
under Group A-4, except that it is usually of diatomaceous or micaceous
character and may be highly elastic as indicated by the high liquid limit.
(2.3) Group A-6: The typical material of this group is a plastic clay soil usually
having 75% or more passing the 0.075-mm sieve. The group includes also
mixtures of fine clayey soil and up to 64% of sand and gravel retained on the
0.075-mm sieve. Materials of this group usually have high volume change
between wet and dry states.
(2.4) Group A-7: The typical material of this group is similar to that described
under Group A-6, except that it has the high liquid limits characteristic of
Group A-5 and may be elastic as well as subject to high volume change.
(2.4.1) Subgroup A-7-5 includes those materials with moderate plasticity
indexes in relation to liquid limit and which may be highly elastic as
well as subject to considerable volume change.
(2.4.2) Subgroup A-7-6 includes those materials with high plasticity indexes in
relation to liquid limit and which are subject to extremely high volume
change.
Note 2: Highly organic soils (peat or muck) may be classified as an A-8 group. Classifi-
cation of these materials is based on visual inspection, and is not dependent
on percentage passing the 0.075-mm (No. 200) sieve, liquid limit or plasticity
index. The material is composed primarily of partially decayed organic matter,
generally has a fibrous texture, dark brown or black color, and odor of decay.
These organic materials are unsuitable for use in embankments and sub-
grades. They are highly compressible and have low strength.
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