ASTM International

Standard Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of Soils
 N D4318

Annotation

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

Two methods for preparing test specimens are provided as follows: Wet preparation method, as described in 10.1. Dry preparation method, as described in 10.2. The method to be used shall be specified by the requesting authority. If no method is specified, use the wet preparation method.

The liquid and plastic limits of many soils that have been allowed to dry before testing may be considerably different from values obtained on non-dried samples. If the liquid and plastic limits of soils are used to correlate or estimate the engineering behavior of soils in their natural moist state, samples should not be permitted to dry before testing unless data on dried samples are specifically desired.

Two methods for determining the liquid limit are provided as follows: Method A, Multipoint test as described in Sections 11 and 12. Method B, One-point test as described in Sections 13 and 14. The method to be used shall be specified by the requesting authority. If no method is specified, use Method A.

The multipoint liquid limit method is generally more precise than the one-point method. It is recommended that the multipoint method be used in cases where test results may be subject to dispute, or where greater precision is required.

Because the one-point method requires the operator to judge when the test specimen is approximately at its liquid limit, it is particularly not recommended for use by inexperienced operators.

The correlation on which the calculations of the one-point method are based may not be valid for certain soils, such as organic soils or soils from a marine environment. It is strongly recommended that the liquid limit of these soils be determined by the multipoint method.