Bearing Capacity and Shallow Foundations - Elements of Soil Mechanics - page 276

Ultimate bearing capacity, Q u = 653.5 × L × B ′ = 15 174 kN

Q 15174

1

u

Bearing resistance R , = = = 15 174 kN

d

γ

Rv

R
F

15174
2850 1

d

Over-design factor , Γ = = = 5 32 .

.

d

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

Example 9.7: Bearing resistance - undrained & drained

It is proposed to place a 2 m × 2 m square footing at a depth of 1.5 m in a glacial clay soil as shown
in Figure 9.11. The 0.5 m thick footing is to support a 0.4 m × 0.4 m centrally located square column
which will carry a vertical characteristic permanent load of 800 kN and a vertical characteristic
transient load of 350 kN. Take the unit weight of reinforced concrete, γ concrete as 25 kN/m 3 .
The soil has the following properties:

undrained shear strength, c u = 200 kPa
effective cohesion, c ′ = 0 kPa
angle of shearing resistance, φ ′ = 28°
weight density, γ = 20 kN/m 3

The ground water table is coincident with the base of the foundation.
Check compliance of the bearing resistance limit state using Design Approach 1 for:

ii. the short-term state;
ii. the long-term state;

Solution:

(i) Representative actions:
Self weight of concrete:

W = × × + ( B L t B × × − L ( z t ) )× γ

concrete col col concrete

= [( 2 0 2 0 0 5 + . × . × . ) ( 0 4 0 4 1 0 . × . × . )] × 25

= 54 0 kN .

G k = 800 kN
Q k = 350 kN

0.4 m × 0.4 m

1.5 m

0.50 m

2.0 m

Fig. 9.11 Example 9.7.