AASHTO

The AASHTO classification system identifies two general classifications: (1) granular materials having 35 percent or less by weight smaller than 0.074 mm and (2) silt-clay materials having more than 35 percent by weight smaller than 0.074 mm.

Allowable Entries:

Enter up to four classes. Acceptable entries are: A-1, A-1-A, A-1-B, A-2, A-2-4, A-2-5, A-2-6, A-2-7, A-3, A-4, A-5, A-6, A-7, A-7-5, A-7-6, and A-8.

Determination:

1. Use (NSSH Exhibit 618-4) Classification of soils and soil-aggregate mixtures for AASHTO system. Or use comparable reference Guide Sheet 1, (see below) to estimate the AASHTO classification.
2. The classification may be further modified by addition of a group index. The group index is calculated from an empirical formula. [See NSSH 618.20(b)(3)]

Guide Sheet 1 - General relationship of systems used for classifying soil samples

[This table may be used as a guide in classifying soils for which no engineering test data are available. The symbol > means "greater than;" the symbol < means "less than."]

Contact Mike Walker for additional assistance.

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