Civil Engineering Reference
In-Depth Information
8.5.2 Bearing pressures on soil
The resultant of the forces due to the pressure of the soil retained and the weight of the wall subject the
foundation to both direct and bending effects.
Let R be the resultant force on the foundation, per unit length, and let R
v
be its vertical component
(Fig.
8.8a
). Considering unit length of wall:
B
2
Section modulus of foundation
=
6
R
B
6
R e
B
R
B
6
e
B
v
v
v
Maximum pressure on base Direct pressure pressure due to b
=
+
ending
=
+
=
1
+
2
R
B
6
e
B
v
Minimum pressure on base
1
=
−
The formulae only applies when R
v
is within the middle third; when R
v
is on the middle third (Fig.
8.8b
),
then:
=
6
e
2
R
B
v
⇒
Maximum pressure
=
,
Minimum pressure
=
0
If the resultant R lies outside the middle third (Fig.
8.8c
) the formulae become:
2
3
R
x
v
Maximum pressure
=
;
Minimum pressure
=
0
8.5.3 Base resistance to sliding
Granular soils and drained clays
The base resistance to sliding is equal to R
v
tan
δ
where
δ
is the angle of friction between the base of the
wall and its supporting soil, and R
v
is the vertical reaction on the wall base. In limit state design, the sliding
Fig. 8.8
Bearing pressures due to a retaining wall foundation.
