AASHTO Soil Classification System
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 sieve)||Silt-Clay Materials (>35% passing the 0.075 mm sieve)|
|Sieve Analysis, % passing|
|2.00 mm (No. 10)||50 max||…||…||…||…||…||…||…||…||…||…|
|0.425 (No. 40)||30 max||50 max||51 min||…||…||…||…||…||…||…||…|
|0.075 (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|
Note (1): 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
- Hogentogler, C.A.; Terzaghi, K. (May 1929). "Interrelationship of load, road and subgrade". Public Roads: pp.37–64.