AASHTO Soil Classification System Guide

The AASHTO classification system was created in 1928 and is one of the first engineering classification systems. The system was developed for use in highway construction and rates soils for their suitability for support of roadway pavements. Soil material under the AASHTO system only includes soils which pass the 3-inch sieve. Note that some specifications described in the following content may not be the same as the specifications followed by your agency. Always check with your State agency’s standards and specifications when using these guidelines.

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