PLASTIC LIMIT TEST
OBJECTIVE
For determination of the plastic
limit of soil.
REFERENCE STANDARD
IS : 2720(Part 5)-1985- Methods of
test for soils : Determination of liquid and plastic limit.
EQUIPMENT & APPARATUS
§ Oven
§ Balance (0.01 g accuracy)
§ Sieve [425 micron]
§ Flat glass surface for rolling
Fig:-Showing
Crumbled thread of 3mm diameter
PREPARATION SAMPLE
After receiving the soil sample it
is dried in air or in oven (maintained at a temperature of 600C). If
clods are there in soil sample then it is broken with the help of wooden
mallet. The soil passing 425 micron sieve is used in this test.
PROCEDURE
1.
A soil sample of 20 gm. passing 425
micron IS sieve is to be taken.
2.
It is to be mixed with distilled
water thoroughly in the evaporating dish till the soil mass becomes plastic
enough to be easily moulded with fingers.
3.
It is to be allowed to season for
sufficient time, to allow water to permeate throughout the soil mass.
4.
10 gms. of the above plastic mass is
to be taken and is to be rolled between fingers and glass plate with just
sufficient pressure to roll the mass into a thread of uniform diameter
throughout its length. The rate of rolling shall be between 60 and 90 stokes
per minute.
5.
The rolling is to be continued till
the thread becomes 3 mm. in diameter.
6.
The soil is then kneaded together to
a uniform mass and rolled again.
7.
The process is to be continued until
the thread crumbled with the diameter of 3 mm.
8.
The pieces of the crumbled thread
are to be collected in a air tight container for moisture content
determination.
Table:-Observation table for moisture content of soil sample
Determination
number
|
1
|
2
|
3
|
Average
|
Moisture
container number
|
3
|
M
|
I
|
|
Wt. of
container g.
|
26.43
|
25.88
|
26.03
|
|
Wt. of
container + wet soil, g
|
31.28
|
30.27
|
31.94
|
20.15
|
Wt. of
dry soil , g
|
30.44
|
29.58
|
30.92
|
|
Wt. of
Water ,g
|
.84
|
0.69
|
1.02
|
|
Moisture
content, %
|
20.95
|
18.65
|
20.86
|
|
REsult
The Plastic limit is to be
determined for at least three portions of soil passing 425 micron IS sieve.
Plastic limit =
20.15
PRECAUTIONS
§ Soil used for plastic limit determination should not be oven
dried prior to testing.
§ After mixing the water to the soil sample , sufficient time
should be given to permeate the water throughout out the soil mass
§ Wet soil taken in the container for moisture content
determination should not be left open in the air, the container with soil
sample should either be placed in desiccators or immediately be weighed.
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