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Stresses in the soil

Soils do not form continous,

uniform mass, they aremade up of a skeleton

of solid grains

Loads induce intergranular

forces (with normal and

tangential components;N,T)

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Effective and neutral stresses in saturated soils

Total stress = Effective stress + neutral stress

'th =

wwhu =

u+=

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Stresses due self weight under static condition

(effective & neutral stresses)

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Water flow Energy equation

Water flow occurs when the energy of thewater differs at various points within the soilmass.

The total energy of the water:

Where:

h: total headz: elevation head

u: water pressurew: unit weight of water

v: velocity

g: acceleration due to gravity

Difference in the potential between two points water flow

Hydraulic gradient:

gvuzh

w 2

2

++=

v

u

zhpotentialg

v

+= :02

2

l

h

i

=

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Stresses due to downward flow

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Stresses due to downward flow

vv

( )wsatwsatwsat ihh

hhhh +=

+=+= '''

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Stresses due to upward flow

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Stresses due to upward flow

!!

""

#$#$

%%&'&' ((

( )wsatwsatwsat ihh

hhhh =

== '''

wi w

sat

===

w

wsatcritwcritwsat ii

0

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Water flow in soils

small voids

small velocity

laminar flow

Darcys law:

where:

k: coefficient of permeability

i: hydraulic gradient

v: velocity

ikv =

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laboratory tests

constanthead testfallinghead test

permeability test in the field

pumping test in situ permeameters

empirical relations

Kozeny Jky

Terzaghi

Determination of coefficient of permeability

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Laboratory determination of coefficient of permeability

Constant head testSoils to analyze:

10-2 m/s k 102 m/s

The coefficient of permeability can becalculated with thw followig formula:

htA

lQ

i

vk

==

)) !!

!!

** !!

h:h: differencedifference inin thethe waterwater levellevel

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Laboratory determination of coefficient of permeability

Falling head test

Soils to analyze

Low permeability soils10-9 m/s k 10-1 m/s

Vizsglat:

1. Minta beksztse az alulrl szitaszvettelelltott kiszrhengerbe.

2. Minta teltse kapillris ton.

3. A szivrgs megindulsa utna klnbzidpontokban nyomsmagassg leolvassa.

4. A minta mreteibl valamint a leolvasottadatokbl k rtke meghatrozhat:

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2

1

12

ln1

h

h

ttl

A

ak

=

++

** !!

,, ,,-.-.

// thethe headhead differencedifference atat tt22

Laboratory determination of coefficient of permeability

Falling head test

Soils to analyzeLow permeability soils

10-9 m/s k 10-1 m/s

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Estimation of coefficient of permeability

Hazen:

Terzaghi:

Kozeny:

( )2

105.10.1 dk =

22

10200 edk =

e

edCk v

+

=

1

3

2

10

( )

( )23

1

1

3

2

12

1

1

ee

eekk

+

+=