LIQID LIMIT TEST
OBJECTIVE
For determination of the liquid
limit of soil using casagrande apparatus.
REFERENCE STANDARD
IS : 2720(Part 5)-1985- Methods of
test for soils : Determination of liquid and plastic limit.
EQUIPMENT & APPARATUS
§ Oven
§ Balance (0.01g accuracy)
§ Sieve [425 micron]
§ Casagrande apparatus
Fig:-Showing
Liquid limit test sample
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.
About 120 gm. of air dried soil from
thoroughly mixed portion of material passing 425 micron IS sieve is obtained.
2.
Distilled water is mixed to the soil
thus obtained in a mixing disc to form uniform paste. The paste shall have a
consistency that would require 30 to 35 drops of cup to cause closer of
standard groove for sufficient length.
3.
A portion of the paste is placed in
the cup of casagrande device and spread into portion with few strokes of
spatula.
4.
It is trimmed to a depth of 1 cm. at
the point of maximum thickness and excess of soil is returned to the dish.
5.
The soil in the cup is divided by
the firm strokes of the grooving tool along the diameter through the centre
line of the follower so that clean sharp groove of proper dimension is formed.
6.
Then the cup is dropped by turning
crank at the rate of two revolutions per second until two halves of the soil
cake come in contact with each other for a length of about 12 mm. by flow only.
7.
The number of blows required to
cause the groove close for about 12 mm. is recorded.
8.
A representative portion of soil is
taken from the cup for water content determination.
9.
The test is repeated with different
moisture contents at least 3 times for blows between 10 and 40.
Table:-Observation table for liquid limit
Determination
number
|
1
|
2
|
3
|
4
|
Number
of blows
|
16
|
19
|
32
|
41
|
Moisture
container
|
F
|
B
|
1
|
2
|
Wt. of
container g.
|
16.10
|
16.62
|
27.16
|
26.20
|
Wt. of
container + wet soil, g
|
29.33
|
29.51
|
38.67
|
39.19
|
Wt. of
dry soil , g
|
25.64
|
26.54
|
36.93
|
38.21
|
Wt. of
Water,g
|
3.69
|
2.97
|
1.74
|
0.98
|
Wt. of content,
%
|
38.68
|
29.94
|
17.81
|
8.16
|
CALCULATION
A ‘flow curve’ is to be plotted on a semi-logarithmic graph
representing water content in arithmetic scale and the number of drops on
logarithmic scale.
§ The flow curve is a straight line drawn as nearly as possible
through four points
§ The moisture content corresponding to 25 blows as read from
curve is the liquid limit of that soil
REsult
The liquid limit is = water content
at 25 blows = 24.00
PRECAUTIONS
§ Soil used for liquid limit determination should not be oven
dried prior to testing.
§ In LL test the groove should be closed by the flow of soil
and not by slippage between the soil and the cup
§ 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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