AASHTO M 145:2012 Standard Specification for Classification of Soils and Soil-Aggregate Mixtures for Highway Construction Purposes

AASHTO M 145:2012 Standard Specification for Classification of Soils and Soil-Aggregate Mixtures for Highway Construction Purposes. 5.1.3.1. Subgroups A-2-4 and A-2-5 include various granular materials containing 35 percent or less passing the 75-gm (No. 200) sieve and with a minus 0.425-mm (No. 40) portion having the characteristics of the A-4 and A-S groups. These groups include such materials as gravel and coarse sand with silt contents or plasticity indexes in excess of the limitations of Group A-I, and fine sand with nonplastic silt content in excess of the limitations of Group A-3. 5.1.3.2. Subgroups A-2-6 and A-2-7 include materials similar to those described under Subgroups A-2-4 and A-2-5 except that the fine portion contains plastic clay having the characteristics of the A-6 or A-7 group. Note 2—Classification of materials in the various groups applies only to the fraction passing the 75-mm (3-in.) sieve. Therefore, any specifications regarding the use of A-I, A-2. or A-3 materials in construction should state whether boulders retained on the 75-mm (3-in.) sieve are permitted. 5.2.1. Group A-4—-The typical material of this group is a nonpiastic or moderately plastic silty soil usually having 75 percent or more passing the 75-gm (No. 200) sieve. The group includes also mixtures of fine silty soil and up to 64 percent of sand and gravel retained on 75-gm (No. 200) sieve. 5.2.2. Group A-i 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. 5.2.3. Group A-6-—The typical material of this group is a plastic clay soil usually having 75 percent or more passing the 75-gm (No. 200) sieve. The group also includes mixtures of fine clayey soil and up to 64 percent of sand and gravel retained on the 75-gm (No. 200) sieve. Materials of this group usually have high-volume change between wet and dry states. 5.2.4. Group A-7——The typical material of this group is similar to that described under Group A-6, except that it has the high liquid limits characteristic of the A-5 group and may be elastic as well as subject to high-volume change. 5.2.4.1. Subgroup A-7-5 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. 5.2.4.2. Subgroup A-7-6 includes those materials with high...