Civil Engineering Reference
In-Depth Information
Figure 21.13
Submerged slopes with no seepage.
21.7 Influence of seepage on the stability of
infinite slopes
In Sec. 21.5 I examined the pore pressures in infinite slopes with different seepage
conditions near the slope and we can now investigate how these different pore pressures
influence the critical slope angle. In the previous section I used upper and lower bound
analyses and showed that the critical angle of a slope in dry soil is
i
c
=
φ
c
. In this
section I will use the limit equilibrium method.
Figure 21.14(a) shows a mechanism consisting of a slip surface parallel to the slope
at a depth
z
and the forces acting on a block length
l
down the slope and Fig. 21.14(b)
is the polygon of forces acting on the block. These are the weight
W
, the shear force
T
=
τ
l
and the total normal force
N
n
l
which is made up of an effective normal
force
N
=
σ
n
l
and a pore pressure force
U
=
σ
=
ul
.
From the force polygon
T
=
φ
c
N
tan
i
c
=
(
N
−
U
) tan
(21.27)
Figure 21.14
Limit equilibrium solution for an infinitely long slope with steady state seepage
parallel with the slope.
