Classification of soils for road-construction purposes
The AASHTO Soil Classification System was developed by the American Association of State Highway and Transportation Officials, and is used as a guide for the classification of soils and soil-aggregate mixtures for highway construction purposes. The classification system was first developed by Hogentogler and Terzaghi in 1929,[1] but has been revised several times since.
AASHTO Soil Classification System (from AASHTO M 145 or ASTM D3282)
| General Classification
|
Granular Materials (35% or less passing the 0.075 mm (No. 200) sieve)
|
Silt-Clay Materials (>35% passing the 0.075 mm (No. 200) sieve)
|
| Group Classification
|
A-1
|
A-3
|
A-2
|
A-4
|
A-5
|
A-6
|
A-7
|
| A-1-a
|
A-1-b
|
A-2-4
|
A-2-5
|
A-2-6
|
A-2-7
|
A-7-5 A-7-6
|
| Sieve Analysis, % passing
|
|
| 2.00 mm (No. 10)
|
50 max
|
…
|
…
|
…
|
…
|
…
|
…
|
…
|
…
|
…
|
…
|
| 0.4255 mm (No. 40)
|
30 max
|
50 max
|
51 min
|
…
|
…
|
…
|
…
|
…
|
…
|
…
|
…
|
| 0.0755 mm (No. 200)
|
15 max
|
25 max
|
10 max
|
35 max
|
35 max
|
35 max
|
35 max
|
36 min
|
36 min
|
36 min
|
36 min
|
| Characteristics of fraction passing 0.425 mm (No. 40)
|
|
| Liquid Limit
|
…
|
…
|
40 max
|
41 min
|
40 max
|
41 min
|
40 max
|
41 min
|
40 max
|
41 min
|
| Plasticity index
|
6 max
|
N.P.
|
10 max
|
10 max
|
11 min
|
11 min
|
10 max
|
10 max
|
11 min
|
11 min1
|
| Usual types of significant constituent materials
|
stone fragments, gravel and sand
|
fine sand
|
silty or clayey gravel and sand
|
silty soils
|
clayey soils
|
| General rating as a subgrade
|
excellent to good
|
fair to poor
|
Plasticity index of A-7-5 subgroup is equal to or less than the LL - 30. Plasticity index of A-7-6 subgroup is greater than LL - 30.
References
- ^ Hogentogler, C.A.; Terzaghi, K. (May 1929). "Interrelationship of load, road and subgrade". Public Roads: 37–64.
See also
