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Structural Concrete - Hassoun

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14.10 Drainage 507<br />

Figure 14.12<br />

Example 14.2: Forces acting on retaining wall.<br />

footing, area = 10.5 × 1 = 10.5 ft 2 .<br />

I = 1 × (10.5)3<br />

12<br />

q 1 = R A + (Re)C<br />

I<br />

= 96.47ft 4<br />

= 18.44<br />

10.5<br />

= 1.76 + 1.37 = 3.13 ksf < 4ksf<br />

q 2 = 1.76 − 1.37 = 0.39 ksf<br />

+<br />

(18.44 × 1.36)×5.25<br />

96.47<br />

Soil pressure is adequate.<br />

5. Calculate the factor of safety against sliding. A minimum factor of safety of 1.5 must be<br />

maintained.<br />

Force causing sliding = H a1 + H a2 = 1.76 + 5.67 = 7.43 K<br />

Resisting force = μR = 0.5 × 18.44 = 9.22 K<br />

Factor of safety against sliding = 9.22 = 1.24 < 1.5<br />

7.43<br />

The resistance provided does not give an adequate safety against sliding. In this case, a key<br />

should be provided to develop a passive pressure large enough to resist the excess force that causes

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