Atterberg Test (Liquid and Plastic Limits; Plasticity Index)

Summary

This video tutorial provides a detailed guide for performing soil tests to determine liquid and plastic limits. It begins with preparing the soil sample, ensuring proper moisture content, and setting aside portions for testing. The process includes a series of precise steps for measuring drop height, recording blow counts, and observing closure measurements. The video emphasizes careful handling and cleaning of equipment between tests. Additionally, it demonstrates the plastic limit testing by forming and drying soil worms. The culmination of the procedure involves weighing and baking the samples for accurate results, making it essential for soil classification and engineering applications.

Takeaways

• 😀 Proper soil preparation is essential, following ASTM D421 standards.
• 🔍 Check the drop height of the dish to ensure accurate testing.
• 👂 Listen for a faint click when setting the dish to confirm correct placement.
• 💧 Gradually add water to the soil while stirring until it reaches a cohesive state.
• 📏 Set aside a sample for plastic limits weighing approximately 20 grams.
• 📊 Conduct the liquid limit test by counting blow rates to observe soil behavior.
• 🧼 Clean the testing dish between points to avoid contamination.
• 🔄 If the blow count for the second point is higher than the first, discard the first result.
• 🌱 For the plastic limit test, roll the soil into thin worms to check consistency.
• 🔥 Dry the soil fragments in an oven overnight for accurate weight measurements.

Q & A

What is the purpose of adding soil to the dish prepared via ASTM D421?

The soil is added to the dish to perform tests that evaluate its plastic and liquid limits, which are essential for understanding soil behavior under different moisture conditions.

How should the drop height of the dish be checked?

The drop height should be checked using a block, ensuring that the dish is positioned halfway over the contact surface and that there is a faint audible click with minimal movement.

What technique is used to wet the soil effectively?

Water is added gradually to the soil while stirring, ensuring that it becomes cohesive. Grooves are cut into the soil to promote even distribution of water.

What should be done once the soil reaches the cohesive state?

A piece of the soil, approximately 20 grams, should be set aside for testing the plastic limits.

How is air removed from the soil in the dish?

Air bubbles are removed by placing a spatula flat on the surface and raking it towards oneself, followed by a second raking to ensure a smooth spread.

What is the procedure for counting blows during the test?

A trough is cut using a grooving tool, and the blow count should be conducted at a rate of approximately 2 blows per second, with the first point aiming for a closure of about 13mm.

What happens if the blow counts for the second point exceed those of the first point?

If the blow counts for the second point are higher, the first point should be discarded, and the second point will then be considered the new first point.

What is the significance of the blow counts for the third point?

The blow count for the third point should range between 15-25 blows, with at least one point being below 25 blows to ensure accurate liquid limit testing.

How should the ball set aside for the plastic limits be prepared?

The ball should be rolled in dry soil to help it dry faster before proceeding with testing.

What is the final step in preparing the soil samples for the oven?

The fragments of soil should be approximately 3/8 inches long and equally distributed among the tare weights before being placed in a pan and put into the oven overnight at 225°F (110°C).