Civil Engineering Reference
In-Depth Information
Figure 24.10
Active forces on walls - undrained loading.
Compare Eqs. (24.9) and (24.l0) for undrained loading with Eqs. (24.3) and (24.4)
for drained loading. For undrained loading the earth pressure coefficients are expressed
as a difference
σ
v
. This is a
consequence of the fundamental difference between the basic equations for drained
and undrained strength.
σ
h
/
(σ
−
σ
)
while for drained loading they are a ratio
v
h
24.9 Overall stability
The forces on a retaining wall arise from the active and passive earth pressures, from
free water pressures and from loads in props and anchors. For overall stability the
forces and moments arising from these pressures must be in equilibrium. For the
simplified example shown in Fig. 24.11,
H
w
0
σ
w
d
z
H
0
σ
h
d
z
P
+
=
(24.13)
where the integrals are simply the areas under the pressure distribution diagrams. In
order to take moments it is necessary to determine the moment arm of each force;
Figure 24.11
Influence of free water on the loads on a retaining wall.
