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AASHTO Soil Classification System
Classification of soils for road-construction purposes
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, but has been revised several times since.
| 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-1-a | A-1-b | A-2-4 |
| Sieve Analysis, % passing | ||
| 2.00 mm (No. 10) | 50 max | ... |
| 0.4255 mm (No. 40) | 30 max | 50 max |
| 0.0755 mm (No. 200) | 15 max | 25 max |
| Characteristics of fraction passing 0.425 mm (No. 40) | ||
| Liquid Limit | ... | ... |
| Plasticity index | 6 max | N.P. |
| Usual types of significant constituent materials | stone fragments, gravel and sand | fine sand |
| 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
References
- Hogentogler, C.A.. (May 1929). "Interrelationship of load, road and subgrade". Public Roads.
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