Atterberg Limits

Test Methods

AASHTO Designation: T 89, “Standard Method of Test for Determining the Liquid Limit of Soils”

AASHTO Designation: T 90,”Standard Method of Test for Determining the Plastic Limit and Plasticity Index of Soils”

Summary of Test Method

The Liquid Limit of a soil is that water content at which the soil passes from a plastic to a liquid state. The plastic limit of a soil is the lowest water content at which the soil remains plastic.

The plasticity index of a soil is the range in water content, expressed as a percentage of the mass of the oven-dried soil, within which the material is in a plastic state. It is the numerical difference between the liquid limit and plastic limit of the soil.

Minimum Sample Size

1 lb

Last Updated September 29, 2005

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