3. Classification of Soil (AASHTO)

Question 1

Two commonly classification system used are:

Answer 1

1. American Association of State Highway and Transportation Officials (AASHTO) System (preferred by Transportation engineers).
2. Unified Soil Classification System (USCS) (preferred by geotechnical engineers)

Question 2

This system was originally developed by Hogentogler and Terzaghiin 1929 as the Public Roads Classification System. Afterwards, there are several revisions. The present AASHTO (1978) system is primarily based on the version in 1945.

Answer 2

AASHTO SYSTEM

Question 3

The AASHTO SYSTEM is based on the following three soil properties:

Answer 3

i. Particle-size distribution (AASHTO T-11 andAASHTO T-27 test)
ii. Liquid Limit (AASHTO T-89 test).
iii. Plasticity Index (AASHTO T-90 test)

Question 4

Large rock fragments that are generally unsuitable for most construction applications due to their size.

Answer 4

Boulder: >300 mm

Question 5

Medium-sized rock fragments that are sometimes used in drainage and foundation applications.

Answer 5

Cobbles: 75 mm – 300 mm

Question 6

4.75 mm – 75 mm

Answer 6

Gravel

Question 7

19 mm – 75 mm

Answer 7

Coarse Gravel

Question 8

4.75 mm – 19 mm

Answer 8

Medium Gravel

Question 8

2.0 mm – 4.75 mm

Answer 8

Fine Gravel

Question 8

0.075 mm – 4.75 mm

Answer 8

Sand

Question 9

0.425 mm – 2.0 mm

Answer 9

Coarse Sand

Question 10

0.075 mm – 0.425 mm

Answer 10

Fine Sand

Question 10

<0.075 mm

These fine-grained soils are classified based on their Atterberg Limits rather than their particle size.

Answer 10

Silt and Clay

Question 11

Separates fine gravel from coarse sand.

Answer 11

No. 10 Sieve (2.0 mm)

Question 12

Separates coarse sand from fine sand.

Answer 12

No. 40 Sieve (0.425 mm)

Question 13

The boundary between sand and silt/clay.

Answer 13

No. 200 Sieve (0.075 mm)

Question 14

Grain Size: Fraction passing #10 sieve and retained #200 sieve

Answer 14

Sand

Question 14

Grain Size: Fraction passing 75mm sieve and retained on #10 (2mm) US sieve

Answer 14

Gravel

Question 15

Grain Size: Fraction passing #200 sieve.

Answer 15

Silt and Clay

Question 16

Plasticity: Term ____ is applied when fine fractions have a PI ≤ 10

Answer 16

silty

Question 17

Plasticity: Term ____ is applied when fine fractions have PI > 10

Answer 17

clayey

Question 18

Groups: Soils are classified into eight groups, ____ through ____.

Answer 18

A-1 through A-8

Question 19

Groups: The major groups A-1,A-2, and A-3 represent the _______ soils.

Answer 19

coarse-grained soils

Question 20

Groups: The A-4, A-5, A-6, and A-7 represent _______ soils.

Answer 20

fine grained soils

Question 21

Groups: The ____ are identified by visual inspection.

Answer 21

A-8

Question 26

Granular materials: 35% or less of total sample passing No. 200

Answer 26

Excellent to good

Question 27

Silt-Clay materials: more than 35% of total sample passing No. 200

Answer 27

Fair to poor

Question 28

helps evaluate how good a soil is for use as a highway subgrade material (the foundation under roads)

Answer 28

Group Index

Question 29

A lower GI = ____ soil quality (good for roads).

Answer 29

better

Question 30

A GI of 0 = _____.

Answer 30

best quality

Question 31

____ GI means the soil is weaker for subgrade use. (Higher or Lower)

Answer 31

Higher

Question 32

Groups like A-1-a, A-1-b, A-2-4, A-2-5, and A-3 always have GI = ____.

Answer 32

0 (considered good soil)

Question 33

If GI is negative, it’s still considered ___.

Answer 33

0

Question 34

Well-graded mixtures of stone fragments or gravel ranging from coarse to fine with a non-plastic or slightly plastic soil binder. However, this group also includes coarse materials without soil binder.

Answer 34

Group A-1

Question 35

Materials consisting predominantly of stone fragments or gravel, either with or without a well graded soil binder.

Answer 35

Subgroup A-1-a

Question 36

Materials consisting predominantly of coarse sand either with or without a well-graded soil binder.

Answer 36

Subgroup A-1-b

Question 37

This material consists of fine sands with little coarse material or soil binder, like beach or desert sand, and some non-plastic silt. It’s suitable for pavements when damp but prone to erosion. It can be compacted with vibratory, pneumatic-tired, or steel-wheeled rollers, but not sheepsfoot rollers.

Answer 37

Group A-3

Question 38

This group includes a wide variety of “granular” materials that 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 containing 35 percent or less passing the 75-μm (No. 200) sieve that cannot be classified as A-1 or A-3.

Answer 38

Group A-2

Question 39

The typical material of this group is a non-plastic or moderately plastic silty soil usually having 75 percent or more passing the 75 μm (No. 200) sieve. The group includes also mixtures of fine silty soil and up to 64 percent of sand and gravel retained on the 75-μm (No. 200) sieve

Answer 39

Group A-4

Question 40

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.

Answer 40

Group A-5

Question 41

The typical material of this group is plastic clay soil usually having 75 percent or more passing the 75-μm (No. 200) sieve. The group includes also mixtures of fine clayey soil and up to 64 percent of sand and gravel retained on the 75-μm (No. 200) sieve.

Answer 41

Group A-6

Question 42

The typical materials and problems of this group are similar to those described under Group A-6, except that they have the high liquid limits characteristic of the A-5 group and may be elastic as well as subject to high volume change.

Answer 42

Group A-7

Question 43

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.

Answer 43

Subgroup A-7-5

Question 44

Includes those materials with high Plasticity Indexes in relation to Liquid Limit and which are subject to extremely high volume change.

Answer 44

Subgroup A-7-6

Question 45

Highly organic soils such as peat or muck are not included in this classification. Because of their many undesirable properties, their use should be avoided, if possible, in all types of construction.

Answer 45

Subgroup A-8