|Description / Abstract
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|This practice describes a system for classifying mineral and
organo-mineral soils for engineering purposes based on laboratory
determination of particle-size characteristics, liquid limit, and
plasticity index and shall be used when precise classification is
NOTE 1—Use of this standard will result in a single
classification group symbol and group name except when a soil
contains 5 to 12 % fines or when the plot of the liquid limit and
plasticity index values falls into the crosshatched area of the
plasticity chart. In these two cases, a dual symbol is used, for
example, GP-GM, CL-ML. When the laboratory test results indicate
that the soil is close to another soil classification group, the
borderline condition can be indicated with two symbols separated by
a slash. The first symbol should be the one based on this standard,
for example, CL/CH, GM/SM, SC/CL. Borderline symbols are
particularly useful when the liquid limit value of clayey soils is
close to 50. These soils can have expansive characteristics and the
use of a borderline symbol (CL/CH, CH/CL) will alert the user of
the assigned classifications of expansive potential.
The group symbol portion of this system is based on laboratory
tests performed on the portion of a soil sample passing the 3-in.
(75-mm) sieve (see Specification E11).
As a classification system, this standard is limited to
naturally occurring soils.
NOTE 2—The group names and symbols used in this test method may
be used as a descriptive system applied to such materials as shale,
claystone, shells, crushed rock, etc. See Appendix X2.
This standard is for qualitative application only.
NOTE 3—When quantitative information is required for detailed
designs of important structures, this test method must be
supplemented by laboratory tests or other quantitative data to
determine performance characteristics under expected field
This standard is the ASTM version of the Unified Soil
Classification System. The basis for the classification scheme is
the Airfield Classification System developed by A. Casagrande in
the early 1940s.2 It became known as the Unified Soil
Classification System when several U.S. Government Agencies adopted
a modified version of the Airfield System in 1952.
This standard does not purport to address all of the safety
concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and
health practices and determine the applicability of regulatory
limitations prior to use.
This practice offers a set of instructions for performing
one or more specific operations. This document cannot replace
education or experience and should be used in conjunction with
professional judgment. Not all aspects of this practice may be
applicable in all circumstances. This ASTM standard is not intended
to represent or replace the standard of care by which the adequacy
of a given professional service must be judged, nor should this
document be applied without consideration of a project's many
unique aspects. The word "Standard" in the title of this document
means only that the document has been approved through the ASTM
2 Casagrande, A., "Classification and Identification
of Soils," Transactions, ASCE, 1948 , p. 901.
*A Summary of Changes section appears at the end of this
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