SYMPOSIA PAPER Published: 01 January 1970

Interim Recommended Practice for the Classification of Soils and Soil-Aggregate Mixtures for Highway Construction Purposes AASHO Designation: M 145-66 I


This recommended practice describes a procedure for classifying soils into seven groups based on laboratory determination of particle-size distribution, liquid limit and plasticity index. Evaluation of soils within each group is made by means of a “group index,” which is a value calculated from an empirical formula. The group classification, including group index, should be useful in determining the relative quality of the soil material for use in earthwork structures, particularly embankments, subgrades, subbases and bases.

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Developed by Committee: D18
Pages: 324–332
DOI: 10.1520/STP38523S
ISBN-EB: 978-0-8031-5570-1
ISBN-13: 978-0-8031-0051-0