Permeability is a property that determines how easily fluid flows through the pores of a material like rock or soil. Gravels are highly permeable while stiff clays are least permeable. Permeability is commonly measured in units called darcies, after the scientist Henry Darcy. Many factors can affect permeability, including pore size, grain size, shape, packing, and the presence of clay. Permeability is important for applications like estimating underground water flow, designing earthworks, and analyzing soil filtration. It can be measured through lab tests like constant head or variable head permeability tests.

1. PERMEABILITY

2. PERMEABILITY
Permeability is a property of a porous material that determines
how easily fluid flows through the interconnected voids of that
material (Rocks/sand).
Gravels highly Permeable
Stiff clay least permeable

4. UNITS
Permeability is defined in the units of area open pore space in the
section that faces or is perpendicular to the direction of flow
 Common Units :
The common units of permeability is DARCY (darcy) , after
name of a scientist .

5. FACTORS AFFECTING
Numerous factors affect the magnitude and the direction of
permeability .
 Textural properties.
• Pore size / grain size
• Grain size distribution
• Shape of grains
• Packing of grains.
 Gas slippage
 Amount, distribution and types of clays

6. CONTI . . .
 Type and amount of secondary porosity.
 Overburden pressure.
 Reactive fluids.
 High velocity flow effects.

7. TYPES OF PERMEABILITY
Types of permeability are the Following :
• Absolute permeability.
• Effective Permeability.

8. Absolute
Permeability
The measurement of
permeability, or ability
to flow or transmit
through a rock,
conducted when a
single fluid or phase is
present in the rock.

9. EFFECTIVE PERMEABILITY
• The ability to preferentially flow or transmit a particular fluid
when other immiscible fluids are present in the reservoir.
• For Instance: Effective permeability of gas in a gas water
reservoir.

10. IMPORTANCE OF
PERMEABILITY
The study of permeability is important for :
• Estimating the quantity of underground water.
• Investigating problems involving pumping seepage of water for
underground construction.
• Analyzing the stability of earth dams and earth retaining walls
subjected to seepage forces.
• The adequate permeable soil and water holding capacity result
In the good plant growth.
• Filters made of soils are designed based upon their
permeability.

11. OPERATIONAL PROCEDURES OF
PERMEABILITY
Coefficient Of permeability :
The coefficient of permeability of a soil describes how easily a
liquid will move through a soil. It is also commonly referred to as
the hydraulic conductivity of a soil. This factor can be affected by
the viscosity, or thickness(fluidity) of a liquid and its density. The
number can also be affected by the void size, or region of non-soil,
void continuity, and soil particle shape and surface roughness. It
is an important factor when determining the rate at which a fluid
will actually flow through a particular type of soil. Coefficient of
permeability depends not only on the properties of soil but also on
the properties of water.

12. DETERMINATION OF COEFFICIENT OF
PERMEABILITY
Capillary permeability
test
Indirect methodsField methods
Laboratory
methods
Constant-head
permeability test
Variable-head
permeability test
Computation from
the particle size
From consolidation test
data
Pumping-in test
Pumping-out test

13. CONSTANT HEAD PERMEABILITY TEST
This test is used to determine the coefficient of permeability of a soil.
This is important in examining the movement of contaminants through
soil or when characterizing flow nets.
• quantity of water that flows under the given hydraulic gradient
through a soil sample of known length and cross-sectional area in a
given time.
• Water is allowed to flow through the cylindrical sample of soil under
a constant head.
• For testing of previous, coarse grained soils

14. K = QL/Aht
K = Coefficient of
permeability
Q = Total quantity of
water
L = Length of the
coarse soil
t = Time
h = Height

15. VARIABLE-HEAD PERMEABILITY
• Relatively for less permeable soil
• Water flows through the sample from a standpipe attached to the top of the
cylinder
• The head of the water (h) changes with the time as flow occurs through the soil.
At different time the head of water is recorded .
𝐾 =
2.30𝑎𝐿
At
log10
h1
h2
T = time
L= length of the fine soil
A= cross sectional area of the soil
a = cross sectional area f tube
K = coefficient of permeability

16. APPLICATIONS OF PERMEABILITY
It is a very important engineering property.it find its applications in many
aspects .
Some of the applications of permeability are following
• Filtration.
• Water treatments.
• Solving problems involving pumping seepage water from
construction excavation.
• The design of earth dams is very much based upon the permeability
of soil used.

17. REFERENCES
• K.R. Arora “Soil machenics and foundation engineering “
• Gopal ranjan and A.S.R.Rao “Basic and applied soil
machanics “
• B.C. Punmia “ Soil machanics and foundation “
• T.Willaim lambe (1969) “ Soil machanics “
• Ernst and sohn ( 2002 ) “ Geotechnical engineering
handbook”

18. Thanks For your
appreciation