Post on 03-Apr-2018
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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
+
+=