Determine The Plastic Limit Of Soil

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This test is done to determine the plastic limit of soil as per IS: 2720 (Part 5) – 1985.The plastic limit of fine-grained soil is the water content of the soil below which it ceases to be plastic. It begins to crumble when rolled into threads of 3mm dia. The apparatus used:

i) Porcelain evaporating dish about 120mm dia.
ii) Spatula
iii) Container to determine moisture content
iv) Balance, with an accuracy of 0.01g
v) Oven
vi) Ground glass plate – 20cm x 15cm
vii) Rod – 3mm dia. and about 10cm long

PREPARATION OF SAMPLE
Take out 30g of air-dried soil from a thoroughly mixed sample of the soil passing through 425µm IS Sieve. Mix the soil with distilled water in an evaporating dish and leave the soil mass for naturing. This period may be upto 24hrs.

Procedure to determine The Plastic Limit Of Soil
i) Take about 8g of the soil and roll it with fingers on a glass plate. The rate of rolling should be between 80 to 90 strokes per minute to form a 3mm dia.

ii) If the dia. of the threads can be reduced to less than 3mm, without any cracks appearing, it means that the water content is more than its plastic limit. Knead the soil to reduce the water content and roll it into a thread again.

iii) Repeat the process of alternate rolling and kneading until the thread crumbles.

iv) Collect and keep the pieces of crumbled soil thread in the container used to determine the moisture content.

v) Repeat the process at least twice more with fresh samples of plastic soil each time.

REPORTING OF RESULTS
The plastic limit should be determined for at least three portions of the soil passing through 425µm IS Sieve. The average water content to the nearest whole number should be reported.

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Comments
  • sharad kumar January 18, 2009 at 4:50 am

    soil test manual

  • sanjeev February 16, 2009 at 7:57 am

    i m student of 6 th sem 4m allahabad agricultural institute deemed university,
    kindly give idea about standard penetration test(spt)

  • tabinda nousheen February 26, 2009 at 5:26 am

    how vl v find softening point of bitumen having 16.4mm penetration

  • B.K.Pradhan May 31, 2009 at 4:13 pm

    Please send new civil engineering development

  • Ramesh January 18, 2010 at 12:55 pm

    I am a civil engineer i want to know that how the safe bearing capacity of soil is calculated please make clear of it and also what is the importance of it

  • binu Samuel March 30, 2010 at 6:52 am

    Dear Sir,

    Can i know how what is mean by CBR for the soil

    • subha August 21, 2010 at 11:20 am

      the CBR stands for California bearing ratio.

  • avinash May 4, 2010 at 9:28 am

    sir why we should use 3mm diameter rolls to determine PL….y not more or less than 3mm

  • avinash May 4, 2010 at 9:29 am

    sir…what happens if v use oven dried sample instead of air dried sample in detrmination of PL

  • Sudhindra H.R June 17, 2010 at 3:26 am

    Please let me know what should be the plastic limit, liquid limit of a soil used for the purpose of backfilling?

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