How To Find Liquid Limit and Plastic Limit – Atterberg Limit Test Procedure – ASTM D4318 – Atterberg Limits
Uses and Importance of ASTM D4318 Procedure
Liquid Limit Casa Grande Apparatus Parts
Today’s test method covers ASTM D4318 The Standard Test Methods for Liquid Limit (LL), Plastic Limit, and Plasticity Index (PI) of Soils Also known as the Atterberg limit tests.
Step 1: The tools required to determine atterberg limits test
The tools required for the liquid limit test are as follows. A Casa Grande apparatus to aid us in getting the blow counts. A grooving tool used to make a standardized groove in the soil pat. A water bottle so we can add moisture to our soil. Four moisture content cans for moisture content determination. A mixing bowl to prepare our soil. A spatula to mix our soil. A mortar and pestle to crush the soil, if need be. A scale to record the weights of each test. A glass plate to roll out our three-millimeter threads on, a rod that is three millimeters in diameter to gauge when we get our plastic limit threads down to three millimeters. Finally, a oven to dry the samples after testing.
This is the atterberg limit test to see how to determine liquid limit and plastic limit test of soil according to ASTM D4318.
Step 2: Start the ASTM D4318 liquid limit test
To get started with the liquid limit test you need to weigh out about 300 grams of the provided soil.
Step 3: Check and see If the soil is clumpy
If the soil is clumpy, you will need to break up the soil in the mortar and pestle equipment.
Step 4: Get ready to add water to the soil sample
Introduce water by adding and then mix the soil until it appears uniform and the soil looks creamy, like peanut butter.
Step 5: Keep in mind
It can take up to 20 minutes to properly blend the soil for the liquid limit test.
Step 6: Followed by recording the weights of the moisture content cans
Get a pencil and paper to record the empty weights of the four moisture content cans. The cans will be used later in the test for moisture content determination.
The Casa Grande apparatus is easily knocked out of calibration, so it is important to calibrate the device often. The grooving tool has a block on the back of it that is exactly 10 millimeters tall, the fall height of the Casa Grande cup. This will help ensure your liquid limit tests provide accurate results.
Step 7: Then calibrate the atterberg limit casa grande apparatus
You will need to calibrate the atterberg limit Casa Grande apparatus.
Step 8: Take the grooving tool and place it under casa grande cup
Take a look at the image above on how you will need to place the grooving tool under the casa grande cup.
Step 9: Next you will rotate the casa grande handle
At this moment you will rotate the handle so that the cam (click to see the casa grande cam) just contacts the cup. If the apparatus is calibrated, the cam will just barely touch the cup and it will not lift it off of the grooving tool.
Step 10: Turn the set screw on the top of the casa grande apparatus
If so, go ahead and loosen the set screw (adjusting screws) on the top of casa grande apparatus.
Step 11: You can adjust the thumb screw in the back
By adjusting the thumb screw in the back of the casa grande apparatus. This will allow you to raise or lower the cup.
Step 12: At this point you need to clean the casa grande cup
Also thoroughly clean and dry the Casa Grande cup, it will ensure nothing can obstruct your test.
The sample is ready and the casa grande apparatus is calibrated you are ready to get started on the liquid limit test. Then followed by the plastic limit test.
Step 13: Spread a moderate amount of soil into the cup
Get the spatula and spread a soil into the casa grande cup as shown above.
Step 14: Using the grooving tool create straight groove
Create a straight groove through the center of the soil pat. The shoulders of the grooving tool should just scrape the surface of the soil pat.
If the shoulders of the grooving tool do not contact the soil pat surface in the atterberg test. This means you did not put enough soil in the cup and the test should be restarted.
Step 15: After the groove has been made
Rotate the handle at 120 revolutions per minute, or two (turns) cycles per second.
Step 16: Count the number of blows
Write down the total the number of blows it takes to close the groove in the soil pat 13 millimeters, or one half inch. This is the width of the grooving tool handle.
Step 17: The number of blows falls between 15 and 20
Scoop out some of the soil and place it in one of the pre-weighed moisture content cans. Then record the new weight for moisture content determination.
Step 18: Set the moisture content can with the wet soil in the oven
Put the liquid limit moisture content can with the wet soil in the oven and reweigh it again in 24 hours.
Step 19: If the number for the liquid limit test falls below 15 blows
Step 20: When the number of blows is above 20
This means your sample is very wet and you need to mix the soil to dry it out and get it to the creamy peanut butter consistency. Keep the casa grande cup clean and dry to repeat the test.
Then your sample is very dry and you need to add moisture to the soil. Again mix the soil and then clean and dry the cup to retest the sample.
You will need to repeat this portion of the atterberg limit test procedure to get test results between:
20 and 25 blows
25 and 30 blows
30 and 35 blows
Once this is complete you will need to plot the moisture content versus the blow counts and determine the liquid limit from the flow chart.
With the moisture content plotted in the vertical axis and the blow counts plotted in the horizontal axis in the log scale, a linear aggression can be established through the data and the liquid limit can be interpolated.
Plastic Limit Test
Step 21: Prepare the test with a 25 to 30 gram sample
While you spread it on the glass plate to dry it out, the sample will get to a workable state. Once it is in a workable state, you can then pick it up and start working it in your hand.
Step 22: Put the soil in your hand
Go ahead and start rolling the soil into a thread. You will roll the soil until the diameter of the thread is reduced to three millimeters.
Step 23: Observe the diameter of soil with the rod
Use the rod so the plastic limit soil test can be a gauged to determine when the soil has reached three millimeters in diameter.
Step 24: After the sample crumbles at three millimeters in diameter
Begin recording the wet weights of the moisture content samples from the plastic limit soil test and place in the oven.
If the plastic limit soil test does not crumble when rolled down to three millimeters, you will need to dry out the soil and start over again.
Step 25: Once the 3 millimeter plastic limit soil sample crumbles
Collect the samples of the crumbling plastic limit soil sample and then place them in the pre-weighed moisture content cans for moisture content determination. You will then repeat the test enough times so that enough soil has been obtained for two moisture content samples of approximately six grams each.
Step 26: Open the oven and place the soil samples in for 24 hours
Make sure to record the wet weights of the moisture content samples and place in the oven. Then you will reweigh the samples again in 24 hours.
The average of the two moisture contents is the plastic limit.
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