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Chapter 4:PERMEABILITYAND SEEPAGEOF SOIL

Faculty of Civil Engineering and Built Environment

Universiti Tun Hussein Onn Malaysia

Presented By:Assoc. Prof. Ts. Dr. Mohamad Yusri Aman

The property of soils

allows

water

to

pass

through

them

at

some

rate.

is

a

product

of

the

granular

nature

of

the

soil,

although

it

can

be

affected

by

other

factors (such as water bonding in clays)

Different

soils

have

different

permabilities,

understanding of

which is critical to the use of

the soil as a foundation or

structural element

Soil and rock are porous materials

Definition of Permeability

4

Why studying flow of water inporous media ???????



To determine the rate of flow of water through soils



To determine the hydraulic conductivity of soils

Importance of Permeability

The design of earth dams is very much based upon thepermeability of the soils used.

The stability of slopes and retaining structures can be greatly affected by the permeability of the soils involved.

Filters made of soils are designed based upon their permeability

Estimating the quantity of underground seepage

Pavement Drainage

Drainage behind Retaining Walls

Practical application

8

Construction ofthe basement ofthe building

Question?



What causes the flow of water through soils?



What law describes the flow of water throughsoils?



What is hydraulic conductivity and how is itdetermined?



What are the typical values of hydraulicconductivity for coarse-grained and fine-grained soils?

10

11

Flow of Water in Soils depends on 

Porosity of the soil



Type of the soil (particle size, particleshape

&

degree of packing)



Viscosity of the fluid (Temperature

&

Chemical Components)



Total head (difference in energy) -Pressure head& Elevation head

13

Bernoulli’s Equation

1. Kinetic energy

datum

z

fluid particle

The energy of a fluid particle ismade of:

2. Strain energy3. Potential energy

• due to

velocity

• due to

pressure

• due to

elevation

(z) with respect to a datum

14

Bernoulli’s Equation

Total head

datum

z

fluid particle

Expressing energy in unit of length:

Velocity head

Pressure head

Elevation head

Z

g

2

u

h

2

w

16

Some Notes

If flow is from A to B,

total head

is higher at

A than at B.

water

A

B

Energy is dissipatedin overcoming the soilresistance and henceis the head loss.

17

Some Notes

Hydraulic gradient (i)

between A and B is the total

head loss per unit length.

A

B

L

L

H

i





L

H

H

2

1





19

Example for Head and hydraulic gradient

Determine the following: a)

The elevation, pressureand total head at points Aand B

b)

The head loss between Aand B

c)

The hydraulic gradientbetween point A and B

Answers: a) point A =7.13m, point B = 6.38m,

b) 0.75mc) 0.

The head Loss ,



h

= h

A

• hB

=(u

A

/



w

• Z

A

) – ((u

B

/



w

• Z

B

)

Hydraulic gradient,

i

=



h/L

Darcy’s law

Where:

A

=

the cross section of soil sample

L

=

the length of the soil sample

h

i

n

is the head at the

inlet

h

out

= the head at the

outlet

Q

= the discharge

q

= the rate of discharge per unit time (t) = Q/t