Civil Engineering Reference
In-Depth Information
Thus the GEO limit state requirement is satisfied and the over-design factor,
150 6
120 8
.
.
Γ =
=
1 25
.
.
2. Combination 2 (partial factor sets A2
+
M2
+
R1)
The partial factors are:
γ
G; fav
=
1.0;
γ
G; unfav
=
1.0;
γ
Q
=
1.3;
γ
φ
′
=
1 2.
. The calcula-
tions are the same as for Combination 1 except that this time these partial factors
are used.
K fill
=
0 31
K foundation soil
a
(
)
.
a
(
)
=
0 37
.
R
=
283 2
.
kN
v d
;
R
=
44 9
.
+
30 4
.
+
32 5
.
+
9 7
.
=
117 5
.
kN
h d
;
R
v ;
tan
δ
=
283 2
.
×
tan
23
° =
120 2
.
kN
Thus the GEO limit state is satisfied and the over-design factor,
120 2
117 5
.
.
1 03
.
.
Γ =
=
Overview
The GEO limit state is satisfied for both checks and thus the proposed design of the
wall is satisfactory. The lowest value of
Γ
obtained (in this case 1.03) governs the design.
Annex C of EN1997-1:2004 also gives formulae which may be used to determine separate active earth
pressure coefficients for surcharge loadings (K
aq
) and for cohesion in the soil (K
ac
). Example
8.1
has no
cohesion (K
ac
=
0) but does have a surcharge. But, as the surface of the soil is horizontal, K
aq
is equal
to K
a
.
Example 8.2:
Strength and stability checks by traditional and
Eurocode 7 approaches
The proposed design of a cantilever retaining wall is shown in Fig.
8.11.
The unit weight of the
concrete is 25 kN/m
3
(EN1991-1-1:2002) and the soil has weight density 18 kN/m
3
. The soil peak
strength parameters are
φ
′
=
38°, c
′
=
0 and the design bearing resistance of the soil beneath the
wall has been calculated to be 250 kPa. The retained soil carries a uniform surcharge of intensity
10 kPa. Ignore any passive resistance from the soil in front of the wall.
Check the safety of the proposed design:
(a) by the traditional (gross pressure) method (assume coefficient of friction between base of wall
and soil to equal tan
′
φ
peak
;
(b) against the GEO (Design Approach 1) limit state of Eurocode 7.
Solution:
Note: When the retained soil is supported by a heel, the design assumes a virtual plane as shown
in Figure
8.11a
provided that the heel width, b satisfies the inequality.
