ASTM D 4318 : 2026

1.1These test methods cover the determination of the liquid limit, plastic limit, and the plasticity index of soils as defined in Section 3 on Terminology.

1.2Two procedures for preparing test specimens are provided as follows: Specimen Preparation Procedure 1 (Wet Preparation), as described in 11.1 and Specimen Preparation Procedure 2 (Dry Preparation), as described in 11.2. The specimen preparation procedure to be used shall be specified by the requesting authority. If no specimen preparation procedure is specified, use the wet preparation procedure. (See Section 6, Interferences.)

1.3Two methods for determining the liquid limit are provided as follows: Liquid Limit Method A (Multipoint Method), as described in Sections 12 and 13, and Liquid Limit Method B (One-Point Method), as described in Sections 14 and 15. The method to be used shall be specified by the requesting authority. If no method is specified, use Method A. (See Section 6, Interferences.)

1.4The plastic limit test, Method for Plastic Limit, is performed on material prepared for the liquid limit test. When determining the plastic limit, two procedures for rolling portions of the test specimen are provided as follows: Plastic Limit Rolling Procedure 1 (Hand Rolling), and Plastic Limit Rolling Procedure 2 (Using the Rolling Device).

1.5The liquid limit and plastic limit of soils (along with the shrinkage limit) are often collectively referred to as the Atterberg limits. These limits distinguished the boundaries of the several consistency states of plastic soils.

1.6The plasticity index, Method for Plasticity Index, is calculated using results from liquid limit and plastic limit testing.

1.7The methods described herein are performed only on that portion of a soil that passes the 425-μm (No. 40) sieve. Therefore, the relative contribution of this portion of the soil to the properties of the sample as a whole must be considered when using these methods to evaluate the properties of a soil.

1.8Units—The values stated in SI units are to be regarded as standard. The values given in parentheses after SI units are provided for information only and are not considered standard.

1.9All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026.

1.10This 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.11This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.