Определение пластичности грунта (plastic limit test)

Plastic Limit Determination

The video demonstrates how to determine a clay soil’s plastic limit in a laboratory. The key visual indicator is the soil’s behavior when rolled into threads about 3 mm in diameter. At the plastic limit, small cracks appear as the threads are rolled. Smooth, uncracked threads indicate that the soil is still too wet, while threads that crumble too soon are too dry.

Method

1. Prepare the soil

   • Mix the clay with water and let it sit for 24 hours.
   • Begin with soil that is moist enough to roll.

2. Roll the soil into threads

   • Roll portions of soil on a clean, flat glass surface.
   • Use a small metal rod as a guide for the target diameter of approximately 3 mm.
   • Work carefully, since achieving a consistent size takes patience.

3. Adjust the moisture

   • Inspect the threads’ surface and how well they hold together.
   • If the threads reach 3 mm but remain smooth and uncracked, the soil is still too wet.
   • Continue rolling or dry the soil slightly using the warmth of your palms, a hair dryer, or a napkin.
   • The desired condition is when small cracks become visible without the threads crumbling prematurely.

4. Prepare samples for weighing

   • Weigh and label three empty cups.
   • Place a sample of the prepared soil into each cup.
   • Weigh each cup with its wet soil and record the measurements.

5. Oven-dry and reweigh

   • Dry the samples in an oven for 24 hours.
   • After drying, weigh each cup and its dry soil.
   • Use the difference between the wet and dry measurements to determine each sample’s moisture content.

6. Calculate the plastic limit

   • Determine the moisture content for all three samples.
   • Calculate the arithmetic mean of the three results. This average is reported as the soil’s plastic limit.

Speakers and Sources

• One presenter/narrator conducts and explains the laboratory demonstration.
• No other identifiable speakers or sources are featured.