Soil permeability refers to a soil's ability to transmit water and air, which is important for fish culture. A pond built in impermeable soil will lose little water through seepage. Permeability is determined by the voids between soil particles and their interconnection, which provides a path for water flow. Laboratory tests measure permeability by timing water flow through a soil sample under constant or falling head. The coefficient of permeability is calculated using measurements of flow rate, head difference, sample length and area.

1. Permeability of Soil
Why is it important to determine soil
permeability?
Soil permeability is the property of the soil to
transmit water and air and is one of the most
important qualities to consider for fish culture.
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2. Permeability of Soil
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A pond built in
impermeable soil will
lose little water
through seepage

3. Permeability of Soil
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• Permeability can be defined as the property of
the soil which enables the flow of water through
it.
There are voids in the soil, which if are
interconnected to each other, provides the path for
the flow of water through it.

4. Permeability of Soil
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The coefficient of permeability depends on the
particle size and various other factors. Some typical
values of coefficient of permeability of different soils
are given in Table Soil Type Permeability in cm/s
Gravel 10 to 1
Coarse sand 1 to 0.1
Medium sand 0.1 to 0.01
Fine sand 0.01 to 0.001
Silty sand 0.001 to 0.0001
Silt 1 x 10-5
clay 1 x 10-7 to 1 x 10-9

5. Permeability of Soil
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Laboratory Measurement of Permeability:
Constant Head Flow
Constant head permeameter is recommended for
coarse-grained soils only since for such soils, flow
rate is measurable with adequate precision.
As water flows through a sample of cross-section
area A, steady total head drop h is measured across
length L.

6. Permeability of Soil Constant Head Flow
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7. Permeability of Soil
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Constant Head Flow
1. Permeameter mould, internal diameter = 100mm,
effective height =127.3 mm, capacity = 1000ml.
2. Detachable collar, 100mm diameter, 60mm height.
3. Dummy plate, 108 mm diameter, 12mm thick.
4. Drainage base, having porous disc.
5. Drainage cap having porous disc with a spring attached
to the top.

8. Permeability of Soil
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Constant Head Flow
• Compaction equipment such as Proctor’s rammer
Constant head water supply reservoir
• Graduated glass cylinder to receive the discharge.
• Stop watch, A meter scale to measure the head
differences and length of specimen.
• Weighing balance accuracy 0.1g
• Filter paper.

9. Permeability of Soil
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Constant Head Flow
Specimen Preparation
• Remove the collar of the mould. Measure the internal
dimensions of the mould.
• Weigh the mould with dummy plate to the nearest gram.
• Apply a little grease on the inside to the mould. Clamp
the mould between the base plate and the extension
collar and place the assembly on a solid base.

10. Permeability of Soil
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Constant Head Flow
Specimen Preparation
• Take about 2.5kg of the soil sample, from a thoroughly mixed
wet soil, in the mould.
• Compact the soil at the required dry density using a suitable
compacting device.
• Take a small specimen of the soil in a container for the water
content determination.
• Remove the collar and base plate. Trim the excess soil level
with the top of the mould.

11. Permeability of Soil
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• Clean the outside of the mould and the dummy
plate. Find the mass of the soil in the mould.
• The mould with the sample is now placed over the
permeameter. This will have drainage and cap
discs properly saturated

13. Permeability of Soil
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Constant Head Flow
Test Procedure
• Through the top inlet of the constant head
reservoir, the specimen is connected.
• The bottom outlet is opened and a steady flow is
established.
• For a particular time interval, the quantity of flow
can be collected.

14. Permeability of Soil
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Constant Head Flow
Test Procedure
• Measure the difference of head (h) in levels
between the constant head reservoir and the outlet
in the base.
• For the same interval, this is repeated three times.

15. Permeability of Soil
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The data that is obtained directly from the tests are:
Length (L) in cm
Area (A) in cm2
Constant Head (h) in cm
Discharge (q) cm3/sec = Q/t
Volume of water collected Q cm3 in t seconds
q = kiA or k = q/iA = q/(h/L)A = qL/(Ah)
Coefficient of permeability k = qL/(Ah) = QL/(Aht)

16. Permeability of Soil - Variable Head test
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Total head h in standpipe of area a is allowed to fall.
Hydraulic gradient varies with time. Heads h1 and h2
are measured at times t1 and t2.
At any time t, flow through the soil sample of cross-
sectional area A is

17. 17
Constant and Falling Head Permeability Test Apparatus

18. Permeability of Soil - Variable Head test
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Apparatus
1. Mould Assembly: The mould assembly including drainage base
and drainage cap which need to be conform to IS: 11209-1985
2. Compaction Hammer
3. Set of Stand Pipes: Glass stand pipes varying in diameter from 5
to 20 mm, suitably mounted on stand or otherwise fixed on wall.
4. Constant Head Tank: A suitable water reservoir capable or
supplying water under constant head.

19. Permeability of Soil - Variable Head test
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Procedure
1. Connect the specimen to the selected stand-pipe through the
top inlet.
2. Open the bottom outlet and record the time interval required
for the water level to fall from a known initial head to a
known final head as measured above the center of the outlet.
3. Refill the stand-pipe with water and repeat the test till three
successive observations give nearly same time interval; the
time intervals being recorded for the drop in head from the
same initial to final values, as in the first determination.

20. Permeability of Soil - Variable Head test
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The following values shall be recorded in the data sheet of
variable head permeability test:
Length of specimen (L)
Diameter of specimen (D)
Volume of specimen (V)
Diameter of stand pipe (d)
Area of stand pipe (a)

21. Permeability of Soil - Variable Head test
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At temperature T of water, the permeability kT is calculated
using the following expression:
kT= ((2.30aL)/(At))Log10(h1/h2)
Where h1: initial head, h2: final head
t: time interval
a: cross-sectional area of the liquid stand pipe
A: cross-sectional area of the specimen
L: length of specimen.