Experiment: Permeability Test by Variable Head Permeameter
Object: To determine the co-efficient of
permeability of soil by variable head permeameter.
Apparatus : 1. Stopwatch,
2. Scale, 3. Permeameter
Theory: The variable head permeameter consists
of a brass-mould in which soil samples can be compacted or undisturbed samples
can be placed. Fine copper wire mesh and perforated plates are fitted at the
top and the bottom of the mould and it is kept in a constant level
rough. The top is connected to a glass-stand-pipe of suitable size. At any
instant, the head of water equals the scale reading (N) , plus the difference
(M) in elevation of the zero of the scale and the water level is the through.
It can be proved on the basis of Darcy’s law for flow through soils that the
coefficient of permeability.
K=
2.3(aL /At ) (log10 h0-log10 h1)
Where, a = area of cross section of the stand pipe
L= length of the soil sample
A= area of cross-section of the soil sample
h0 = initial head of water
Procedure:
1. Water is filled in the standpipe which is being used.
The stopcock at the top of the parameter is closed after the expulsion of all
the air from the rubber tube and the connecting pipe.
2. If the soil is not already saturated, it is left for about 24
hours for saturation, the rough is filled up to the top.
3.The stand pipe is filled with water, almost upto the top,
after tightening the clamp on the rubber tube.
4. The clamp is released, when the water level in the standpipe
starts falling, steadily, it is read and simultaneously the stop watch is
started.
5. The flow of water is stopped when the water level in the
standpipe falls through a sufficient distance as indicated in the table ( see
text page) and the time noted.
6. Five sets of such independent readings are taken and an
average values of the co-efficient of permeability ‘K’ is found out.
Observations and Computations:
Diameter of standpipe :
...........................................................
3.The stand pipe is filled with water, almost upto the top,
after tightening the clamp on the rubber tube.
4. The clamp is released, when the water level in the standpipe
starts falling, steadily, it is read and simultaneously the stop watch is
started.
5. The flow of water is stopped when the water level in the
standpipe falls through a sufficient distance as indicated in the table ( see
text page) and the time noted.
6. Five sets of such independent readings are taken and an
average values of the co-efficient of permeability ‘K’ is found out.
Observations and Computations:
Diameter of standpipe :
.................................................................................
Zero of scale and water level in the rough
(=M) :..........................................
Cross sectional area of
sample : ...................................................................
Cross sectional area of the
standpipe : .........................................................
Height of the
sample : ...................................................................................
Obs. No.
|
Scale
|
reading
|
Time
|
Total
|
Head
|
Value
|
|
N0 (at ti-
me’
|
N1 (at ti-
me’
|
elapsed,
|
at’ t=0
|
at’ t=1
|
of ‘K
|
Average
|
|
t=0
(cm )
|
t=1
( cm )
|
t
(sec)
|
h0= N0+
M (cm)
|
h1= N1+
M (cm)
|
(cm/sec)
|
(cm/sec)
|
|
1
|
80
|
25
|
|||||
2
|
75
|
20
|
|||||
3
|
70
|
15
|
|||||
4
|
65
|
10
|
|||||
5
|
60
|
05
|
......................
Zero of scale and water level in the rough (=M)
Zero of scale and water level in the rough (=M)
AFTER PUTTING THE ALL ABOVE DATA YOU CAN FIND THE PERMEABILITY THROUGH SOIL:
Co-efficient of permeability of
the given soil sample was found to be ....................................
cm/sec.
