Classification of Soils for Engineering Purposes - Soil Properties: Testing, Measurement, and Evaluation - page 147

Table 11-1 AASHTO Classification of Soils and Soil-Aggregate Mixtures [1]

Granular Materials Silt-Clay Materials

General Classification: (35% or less passing 0.075 mm) (more than 35% passing 0.075 mm)

A-1 A-2 A-7

Group Classification: A-1-a A-1-b A-3 A-2-4 A-2-5 A-2-6 A-2-7 A-4 A-5 A-6 A-7-5,

A-7-6

Sieve analysis: percent
passing
2.00 mm (No. 10) 50 max. — — — — — — — — — —

0.425 mm (No. 40) 30 max. 50 max. 51 min. — — — — — — — —

0.075 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. b

Plasticity index 6 max. NP a 10 max. 10 max. 11 min. 11 min. 10 max. 10 max. 11 min. 11 min. b

Usual types of significant Stone fragments, Fine Silty or clayey gravel and sand Silty soils Clayey soils

constituent materials gravel, and sand sand

General rating as subgrade Excellent to good Fair to poor

a NP, nonplastic.
b Plasticity index of A-7-5 subgroup is equal to or less than LL minus 30. Plasticity index of A-7-6 subgroup is greater than LL minus 30 (see Figure 11-1).