Atterberg Limits

SWIS EDUCATION
14 Oct 202003:24

Summary

TLDRThis 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.

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Related Tags
Soil TestingASTM D4318Liquid LimitPlastic LimitCasagrande CupGrooving ToolSoil ScienceLaboratory TestEngineering GeologyMoisture ContentConstruction Materials