Lecture note -22.10.2013
Problem 1:
h = -hϒw =ΔPh
H1
ΔP
H2
No , effecti e st ess σ =σ-u (u= hydrostatic pressure)
u =UTZ
So, the pressure will be P= [(h-z)/H2]ϒw +Zϒw+H1ϒw
Problem2:
Seepage Force:
Zϒ
z
ϒ =ϒsat
Now,
Upward effective stress:
σ uZ=Z (ϒsat-ϒw)-iZϒw
Downward Effective stress:
σ dZ=Z (ϒsat-ϒw)+iZϒw
If P is varying it gives dp/dz
Now, the expressing the seepage force per unit volume is convenient.
So, F/ Adz= [A. (∂p/∂z). dz]/Adz
f =∂zP
f= ∂iP
Pu= ϒ -iϒw
ϒ =iϒw= Δfu=0
N.B- Liquefaction of Solid: A state of 'soil liquefaction' occurs when the effective stress of soil is
reduced to essentially zero, which corresponds to a complete loss of shear strength. This may be
initiated by either monotonic loading (e.g. single sudden occurrence of a change in stress – examples
include an increase in load on an embankment) or cyclic loading (e.g. repeated change in stress
condition – examples include wave loading or earthquake shaking). Quick sand is one of the
interesting examples of li uefaction of solid . Suppose, if we take an empty beaker, and put some
soil grains. First they will be at steady state next they started moving. This movement happens due
to their weights.
Sheet Pile: Sheet piling is an earth retention and excavation support technique that retains soil,
using steel sheet sections with interlocking edges. Sheet pile walls have been used to support
excavations for below grade parking structures, basements, pump houses, and foundations,
construct cofferdams, and to construct seawalls and bulkheads.
The diagram shows the flow net for seepage of water around a single row of sheet piles driven into a
permeable layer.
Now, the force acting on the D/2 area –
i1= H2/L1
i2=H2/L2
i3=H2/L3
If, i1> i2> i3
W= D.D/2(ϒsat - ϒw)
U=0.5D.D.iav.ϒw
If, W<<U
W/U>5
*If there is no water pressure
σ =σ-ua +χ ua-uw)
σ =σ-uw
χs
{χ
% = ,χ
= }
Hence, the graph will be-