Lesson 7 - nptel

where K is the coefficient of permeability and b is the width of one flow channel, that is,
the distance between two stream lines. If Nf is the total number of flow channels, then
the seepage per unit width of the embankment (q) is given as
h ⎛ b ⎞
⎛ b ⎞ ⎛ Ν f ⎞
q = ∑ Δq
= Κ ⋅ ⎜ ⎟ ⋅ Ν = Κ ⋅ ⋅⎜
⎟ ⋅
⎜
⎟
f h
(4)
Ν d ⎝ l ⎠
⎝ l ⎠ ⎝ Ν d ⎠
The above calculations would give the quantity of water seeping through the body of the
dam. Similar calculations have to be done for the quantity of seepage taking place
through the foundation.
4.7.6 Stability calculation
For an embankment dam the most important cause of failure is sliding. It may occur
slowly or suddenly and with or without any prior warning. Such a failure causes a
pportion of the earth or rockfill to slide downwards and outwards with respect to the
remaining part generally along a well-defined slide surface (Figure 53). As may be
observed, the profile of the slide surface may be nearly approximated by circular arcs
(Figure 53 a, b) or by wedges (Figure 53 c, d). The upstream failure surfaces in all
cases may be possible, among others, during sudden drawdown of the reservoir level
from elevation I to II, shown in the figures. At the time of the failure, the average
shearing resistance all along the sliding surface. It is, therefore, necessary that the
designers take special care to estimate the possibility of such a failure.
Version 2 CE IIT, Kharagpur