Lab Report 2
Liquid limit and plasticity test
Drew Kelly and Dennis Johnson
MOREHEAD STATE
UNIVERSITY
Introduction: This lab dealt with finding the liquid limit and plastic limit of the soil sample we
had from lab 1. The first part of the lab was the liquid limit, the second part was the plastic test,
then we had to find the plastic index at the end of the lab. The students got the opportunity to use
different techniques to reach their goals and they will be discussed in the following report. For
the first lab you must get your soil sample and then wet the soil and mix it until it has a good
mixture of water and non is standing.
Test equipment and materials: The first thing that was needed for the lab was a fine collection
of soil that passes through the No. 40 sieve. Then we needed the Atterberg blow machine for the
liquid limit test and just a smooth surface to perform the plastic test.
Test procedures: For the liquid limit test you had to
1) Place prepared soil in cup of the liquid limit device, spread around the cup so it is flat and
smooth.
2) Draw a line from the upper end to the bottom end in the soil that leaves a groove.
3) Lift and drop the cup by turning the lever and a rate of 2 drops per second
4) Record the number of drops that was required to make the groove close up. Twenty-five
is the goal.
5) If the number of drops is more than 25 remix the soil and re do the test until the goal is
reached.
6) Determine the water content for each trial. Water content=Wwet-Wdry/Wdry
Test procedures for the plastic limit:
1) The same soil sample is rolled on the rolling surface until 1/8 inch diameter is reached.
2) The thread s=is broken into pieces which is then squeezed together again, and then rolled
into another thread like the one before.
3) The entire process is repeated until the thread cannot be rolled into another thread, this is
the indicator that the plastic limit has been reached.
4) Then you must again find the water content
Test Results: For this liquid limit test it took group 3 a total of 3 trials to reach the specified
goal of 25 drops for the groove to close up. The first trial the number of drops was in the 50’s so
we had to add more water to increase the water content. On the second trial it was the complete
opposite, a total of 16 drops is what it took to get the gap to close, so then we added dirt to the
mixture to thicken it. The third trial was the one that did it for group 3. It took exactly 25 drops
of the cup to get the groove to close up. The water content is not a very accurate number due to
the scale not being correct, the dry sample of the soil would not register. For the plastic limit, it
took a total of 5 trials to reach the plastic state. For this we had to roll the soil into a 1/8” thread
and repeat it until the soil could not be rolled into a thread any longer. Again the Water content
was the same as the liquid limit since we used the same amount of soil.
Conclusion: this lab showed the relationship between the liquid limit and plastic test by
showing the water content was the same or very close to each other. If the scale had been able to
give us accurate weighing information then its thought that the results may have been different,
but for now groups must assume that all is correct.