Bearing Capacity and Shallow Foundations - Elements of Soil Mechanics - page 272

Ultimate bearing capacity per metre run Q , = 169 2 1 3 . × . = 220 N m run k /

u

Q 220

1

u

Bearing resistance R , = = = 220 kN m run /

d

γ

Rv

R
F

220
108 8

d

Over-design factor , Γ = = = 2 03 .

.

d

Since Γ > 1, the GEO limit state requirement is satisfied.
2. Combination 2 (partial factor sets A2 + M2 + R1)
The calculations are the same as for Combination 1 except that this time the following partial
factors (from Table 5.1) are used: γ G; unfav = 1.0; γ Q = 1.3; γ cu = 1.40; γ Rv = 1.0.

c = 21 4 . kPa

u ;

W = 30 6 . × γ = 30 6 . kN m run /

d G unfav ;

P = 50 0 . × γ = 50 0 . kN m run /

d G unfav ;

F d = 30 6 . + 50 0 . = 80 6 . kN m run /

′ =

e = 0 248 . m B ; 1 3 . m

Q = ( c N s + γ zN ) × ′ = B 125 1 1 3 . × . = 163 1 . kN m run /

u u d c c ; q

Q 163 1

1

.

R

u
Rv

163 1 . kN m run /

= = = d

γ

R
F

163 1
80 6

.

d
d

2 02

Γ = = = .

.

Since Γ > 1, the GEO limit state requirement is satisfied.

Example 9.6: Traditional, and Eurocode 7, approaches (ii)

A concrete foundation 3 m wide, 9 m long and 0.75 m deep is to be founded at a depth of 1.5 m
in a deep deposit of dense sand. The angle of shearing resistance of the sand is 35° and its unit
weight is 19 kN/m 3 . The unit weight of concrete is 24 kN/m 3 .

(a) Using a lumped factor of safety approach (take F = 3.0):
(i) Determine the safe bearing capacity for the foundation.
(ii) Determine the safe bearing capacity of the foundation if it is subjected to a vertical line load
of 220 kN/m at an eccentricity of 0.3 m, together with a horizontal line load of 50 kN/m acting
at the base of the foundation as illustrated in Figure 9.10.
(b) For the situation described in (ii) above, establish the magnitude of the over-design factor for
the Eurocode 7 GEO limit state, using Design Approach 1.