Civil Engineering Reference
In-Depth Information
Example 8.1:
Mass concrete wall; overturning and sliding by
Eurocode 7
Check the proposed design of the mass concrete retaining wall shown in Fig.
8.10a
. The
wall is to be cast into the foundation soil to a depth of 1.0 m and will retain granular fill
to a height of 4 m as shown. Take the unit weight of concrete as
γ
c
=
24 kN/m
3
(from
EN1991-1-1:2002) and ignore any passive resistance from the soil in front of the wall.
Check the overturning and sliding limit states, using Design Approach 1.
Solution:
(a) Overturning:
Since the wall is founded into soil, the ground will contribute to the stability and
therefore overturning is checked using the GEO limit state. For Design Approach 1
we must check both partial factor sets combinations.
1.
Combination 1 (partial factor sets A1
+
M1
+
R1)
First, we determine the design material properties and the design actions:
(i) Design material properties:
Retained fill:
′
tan
φ
tan
.
32
1 0
°
= °
=
′
=
φ
tan
−
1
tan
−
1
32
d
γ
φ
′
Eurocode 7 states that for concrete walls cast into the soil,
δ
should be taken
as equal to the design value of
φ
, i.e.
δ
/
′
=
d
1
. From Figure
8.9,
the horizontal
component of K
a
=
0.25.
Foundation soil:
′
tan
φ
tan
.
28
1 0
°
= °
=
′
=
φ
tan
−
1
tan
−
1
28
d
γ
φ
′
(ii) Design actions
The self-weight of the wall is a permanent, favourable action. Consider the
wall as comprising three areas as indicated in Fig.
8.10a
. The design weight
of each area is determined:
Surcharge, q
=
20 kPa
1.8 m
Retained fill:
c
′ =
0;
φ′ =
32
°
γ =
18 kN/m
3
K
a
×
q
=
0.25× 20
=
5.0 kPa
K
a
×
γ
×
h
=
0.25×18 × 4
=
18.0 kPa
2
4.0 m
1
2.0 m
21.6 kPa
3
6.0 kPa
1.0 m
Foundation soil:
c
′ =
0;
φ′ =
28
°
γ =
20 kN/m
3
27.6 kPa
2.6 m
(a) Retaining wall
(b) Earth pressure diagram (DA1-1)
Fig. 8.10
Example
8.1.
