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Determine The Plastic Limit Of Soil

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

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.


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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Kanwarjot Singh

Kanwarjot Singh is the founder of Civil Engineering Portal, a leading civil engineering website which has been awarded as the best online publication by CIDC. He did his BE civil from Thapar University, Patiala and has been working on this website with his team of Civil Engineers.

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33 comments on "Determine The Plastic Limit Of Soil"

sharad kumar says:

soil test manual

sanjeev says:

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

tabinda nousheen says:

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

B.K.Pradhan says:

Please send new civil engineering development

Ramesh says:

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 says:

Dear Sir,

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

subha says:

the CBR stands for California bearing ratio.

r ksinha says:

yes it the ratio comparing soil with standard crushed stone

avinash says:

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

muzz says:

it is the standard to deviate would compremise the validity of the results

avinash says:

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

Sudhindra H.R says:

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

tadele mulatu says:

10q for getting information

Enayatullah sharifi says:

hi sir. what is the mean idea of the plastic limit and liquid limit and how we can use in fild.

Gajanan says:

Will i get the civil engineering megazine

kks says:

what is the importance of LL and PL of soils for engineers

ramya says:

for what we are doing plastic limit??in field work were&all using it

r ksinha says:

its the basic test which gives info related to omc mdd and also cbr value through which u can calculate overlay and all in field

saifullahi aliyu says:

sir i am a student i want to know how extraction test is carry out?

rans says:

I want to ask a copy for structural civil work checklist on high rise building, thank you.

Yadav Lal Bhattarai says:

For the above experiment report i would like to thank in which technical personal in soil mechanics and foundation engineering can proceed their experiment with these provided instructions and manual. of But the importance of experiment and its uses are not mentioned. the upper limit and too lower limit of water content as per soil type is not specified. I felt it would be very helpful if you could provide the above requested data in tabulated form. It will enhance the Civil Engineering students as well as actual field test performer to soil type and its condition. It will also help to provide safety and precaution for designing structure.

By: Yadav Lal Bhattarai
Civil Engineering Student
Sharda University

Byron Ocampo says:

sir, is it possible to get the value of plastic limit?

kumar khadka says:

please send me the log graph to detrmine liquid limit

kumar khadka says:

is there any software to calculate liquid limit result?

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