Soil Testing
Determining the Plastic Limit and Plasticity Index of Soil
(Referenced Document: ASTM D 4318)
OBJECTIVE: To determine the plastic limit and plasticity index of soil.
APPARATUS AND SUPPLIES
Evaporating dish
Spatula
Ground-glass plate—at least 30 cm (12 in.) square by 1 cm (3⁄8 in.) thick for mixing soil and rolling plastic limit threads
Balance (with accuracy to 0.01 g)
Containers
Oven
PREPARATION OF TEST SPECIMEN
Select a 20-g portion of soil from the material prepared for the liquid limit test, either after the second mixing before the test, or from the soil remaining after completion of the test. Reduce the water content of the soil to a consistency at which it can be rolled without sticking to the hands by spreading and mixing continuously on the glass plate or in the mixing/storage dish. The drying process may be accelerated by exposing the soil to the air current from an electric fan, or by blotting with paper that does not add any fiber to the soil. Paper such as hard surface paper toweling or high wet strength filter paper is adequate.
PROCEDURE
The procedure for determining the plastic limit is quite simple. The soil sample is rolled between the fingers and the rolling surface until a 3.2-mm (1⁄8-in.) diameter thread is obtained. This thread is broken into pieces, which are then squeezed together again. The resulting mass is rolled once more between the fingers and the rolling surface until another thread of the same diameter is obtained. Each time the soil is rolled out, it becomes drier by losing moisture. The entire process is repeated until the thread crumbles and the soil no longer can be rolled into a thread. At this point, the plastic limit is assumed to have been reached, and the water content (which is the plastic limit) is determined.
The actual step-by-step procedure is as follows (ASTM D 4318-05 [1]):
(1) From this plastic-limit specimen, select a 1.5 to 2.0 g portion. Form the selected portion into an ellipsoidal
(Referenced Document: ASTM D 4318)
OBJECTIVE: To determine the plastic limit and plasticity index of soil.
APPARATUS AND SUPPLIES
Evaporating dish
Spatula
Ground-glass plate—at least 30 cm (12 in.) square by 1 cm (3⁄8 in.) thick for mixing soil and rolling plastic limit threads
Balance (with accuracy to 0.01 g)
Containers
Oven
PREPARATION OF TEST SPECIMEN
Select a 20-g portion of soil from the material prepared for the liquid limit test, either after the second mixing before the test, or from the soil remaining after completion of the test. Reduce the water content of the soil to a consistency at which it can be rolled without sticking to the hands by spreading and mixing continuously on the glass plate or in the mixing/storage dish. The drying process may be accelerated by exposing the soil to the air current from an electric fan, or by blotting with paper that does not add any fiber to the soil. Paper such as hard surface paper toweling or high wet strength filter paper is adequate.
PROCEDURE
The procedure for determining the plastic limit is quite simple. The soil sample is rolled between the fingers and the rolling surface until a 3.2-mm (1⁄8-in.) diameter thread is obtained. This thread is broken into pieces, which are then squeezed together again. The resulting mass is rolled once more between the fingers and the rolling surface until another thread of the same diameter is obtained. Each time the soil is rolled out, it becomes drier by losing moisture. The entire process is repeated until the thread crumbles and the soil no longer can be rolled into a thread. At this point, the plastic limit is assumed to have been reached, and the water content (which is the plastic limit) is determined.
The actual step-by-step procedure is as follows (ASTM D 4318-05 [1]):
(1) From this plastic-limit specimen, select a 1.5 to 2.0 g portion. Form the selected portion into an ellipsoidal