Atterberg Limits

Summary

This video demonstrates the Atterberg limit test method, as per ASTM D4318, to determine the liquid and plastic limits of fine-grained soil samples. The process involves preparing a uniform soil paste, conducting the liquid limit test by measuring the number of blows required to close a groove in the soil, and determining water content at different blow counts. The plastic limit test is performed by rolling the soil into a thread until it crumbles, and calculating the average water content from three trials. The results are plotted on a semi-log graph to find the liquid limit at 25 blows and the flow index from the line's slope.

Takeaways

• 🔬 The Atterberg limit test is conducted to determine the liquid limit and plastic limit of fine-grained soil samples as per ASTM D4318.
• 🌡️ The soil sample should be pulverized and sieved to remove large particles before testing.
• 💧 A uniform paste is created by adding water to air-dried soil in an evaporating dish.
• 📏 The soil in the Casagrande cup is smoothed to a maximum depth of 8mm for consistency.
• ⚙️ The grooving tool is used to create a groove in the soil, and the device is cranked at 2 revolutions per second until a clear closure is observed.
• 🔢 The number of blows required to cause closure is counted, and the soil sample is collected for moisture content determination if the count is between 15 to 40.
• 📉 A semi-log graph is plotted with water content on one axis and number of blows on the other to determine the liquid limit at 25 blows.
• 🔄 The test is repeated with different moisture contents to obtain varying blow counts, helping to plot the graph accurately.
• 🌡️ For the plastic limit test, dry soil is mixed with water and rolled into a ball, then rolled out until it crumbles before forming a thread.
• 📝 The water content of the crumpled soil is determined for three trials, and the plastic limit is calculated as the average of these trials.

Q & A

What is the purpose of the Atterberg limit test method?

The Atterberg limit test method is used to determine the liquid limit and plastic limit of fine-grained soil samples, as per ASTM D4318.

What is the first step in preparing the soil sample for the liquid limit test?

The first step is to pulverize the soil sample and pass it through a number 40 sieve to remove all large particles.

How should the drop of the cup be calibrated in the liquid limit test?

The drop of the cup should be calibrated using the other end of the grooving tool to ensure consistency in the height of the drop.

What is the required amount of soil to be placed in the Casagrandes cup for the liquid limit test?

Approximately 250 grams of air-dried soil should be placed into the evaporating dish for the liquid limit test.

What is the maximum depth required when smoothing the soil surface in the Casagrandes cup?

The maximum depth should be about eight millimeters when smoothing the soil surface in the Casagrandes cup.

What is the rate at which the device should be cranked during the liquid limit test?

The device should be cranked at a rate of 2 revolutions per second during the liquid limit test.

How is the number of blows counted in the liquid limit test?

The number of blows is counted until there is a clear visible closure of half an inch (12.7 millimeters) in the soil pad placed in the cup.

What should be done if the count of blows is between 15 to 40 during the liquid limit test?

If the count is between 15 to 40, the sample from the closed part of the cup should be collected, and the water content should be determined.

How is the moisture content determined in the liquid limit test?

The moisture content is determined by measuring the weight of the moisture can before and after placing the moist sample and then drying it in an oven for 24 hours.

What is plotted on a semi-log graph paper in the liquid limit test?

The water content versus the number of blows is plotted on a semi-log graph paper.

How is the liquid limit of the soil sample determined from the graph?

The liquid limit is determined from the graph by finding the water content corresponding to 25 blows.

What is the process for the plastic limit test?

For the plastic limit test, approximately 20 grams of dry soil is mixed with water, rolled into a ball, and the process is repeated until the soil begins to crumble before becoming a thread. The water content of the crumpled soil sample is determined for three trials, and the plastic limit is the average of these trials.