SOIL
PERMEABILITY APPARATUS
Working Manual
OPERATING INSTRUCTIONS
FOR
SOIL PERMEABILITY APPARATUS
OBJECT: To determine
the permeability of a given sample of soil with constant and falling head
method.
SCOPE: A material is said to be permeable, if it contains
continuous voids and such voids are in all types of soils including stiffest
clay and neat cement etc. The permeability
has a great effect on the cost and construction of the engineering works, such
as dams works etc. In water bearing
soils. To make the construction easy the
knowledge of permeability of soil is essential.
SPECIFICATIONS:
Permeability is the property of the soil which indicates the case with which the
water will flow through soil which depends upon the Darcy's law.
q
= AKi
where q
= Discharge through the sample
A
= Cross section area
i = Hydraulic gradient
K
= Constant of proportionality
The coefficient of permeability is
defined as the rate of flow per unit area of the soil under unit hydraulic
gradient, which has the dimensions as that of velocity and is normally denoted
by letter K. The main function of this
test is to know the processed of soil, shape of the voids and size of the
voids. This test is also giving the idea
of density and viscosity of the fluid.
The coefficient of permeability appears
only to a particular fluid (water) and is subjected like viscosity with slight
variation of the temperature.
APPARATUS: Permeameter,
Water source, Graduated cylinder, Meter rod, Stop Watch and Soil sample etc.
TEST PROCEDURE OF PERMEABILITY OF
HIGHLY PERMEABLE SOIL BY CONSTASNT HEAD MEHOD: Take a 0.2 liter core cutter with
dolly. Attach the dolly on the top of
the block of undisturbed soil. Cut the
soil from all round the cutter and dolly. Remove the cutter and dolly full of
soil. Level the bottom of the core
cutter. A fret removing the dolly trims
off the excess of soil firm the top of the cutter. Keep a wire gauge or filter paper on the
perforation of the base plate. Keep the
cutter with sample on the gauge in such a way that the cutter edge will rest on
the gauge. Now keep the top cap on the
cutter, but before keeping the cap the copper wool and washer will be fixed at
proper places. Tide the tope can and
base plate with 4 nuts and blots together.
Keep the assembly in the bottom tank.
Connect the over hand tank with the vertical stem and clamp it
properly. Now fix the Ist tube of
overhead tank with the source of water supply.
The second tube is the over flow tube and will be placed near the drain .
The 3rd tube to be connected to the inlet nozzle of the
permeameter. When this assembly is
completed open the cock of the water source and allow the water to flow. Open the air cock and allow the water to
flow through it until the air is expelled from the apparatus. When the air has been excelled from the
apparatus close the air cock. Saturate
the sample and allow the flow of water through the sample. Measure the discharge for a given time after
the flow has been regulised. Note down the height of the supply source and
calculate the coefficient of
permeability.
Q Z
1
K = X
X
t h
A
K=
Co-efficient of permeability (cm. per second)
Q=
Total discharge in seconds (In cc.)
Z=
Height of the sample (cm.)
A=
Area of the sample (Sq. cm.)
h
= Head causing flow (cm.)
TEST PROCEDURE PERMEABILITY OF LOW PERMEABLE SOIL BY FALLING
HEAD METHOD : Fix the falling head
stand pipe with the permeable rod instead of over head tank. Take the sample in the same way as in the case
of constant head method. Now allow the
sample to saturate. When the constant
flow is set, release the cock. Note the
level of water in the tube and open the Pinch Cock and take the discharge in a
know interval of time. Note the drop in
head.
Coefficient of the permeability
2.3
x Z x a h 1
K
= log 10
At h 2
K=
Co-efficient of permeability
A=
Area of sample (sq. cm.)
a
= Interial area of the glass pipe (sq. cm.)
Z=
Length of the sample (cm.)
h1=Head
of the water at the start of the reading
h2=Head
at the end of the observation
t
= Time in seconds
PRECAUTIONS :
- The sample should be free from air.
- The head should be constant through out the
experiment.
- The flow should be constant.
- There should not be any air bubble at the top of
the tank throughout the experiment.
- The unit of calculations should be same
throughout the calculations.
- The apparatus should be clean.
- There should not be any leakage between the base
plate and the top cap from sides.
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