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Question 6.6: A rectangular raft of size 30 x 12 m founded on the ground s...

A rectangular raft of size 30 x 12 m founded on the ground surface is subjected to a uniform pressure of 150 kN / m ^{2}. Assume the center of the area as the origin of coordinates (0,0), and corners with coordinates (6, 15). Calculate the induced stress at a depth of 20 m by the exact method at location (0, 0).

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Divide the rectangle 12 x 30 m into four equal parts of size 6 x 15m.

The stress below the corner of each footing may be calculated by using charts given in Fig. 6.7 or Fig. 6.8. Here Fig. 6.7 is used.

 

For a rectangle 6 \times 15 m , z / b=20 / 6=3.34, l / b=15 / 6=2.5.

 

For z / b=3.34, l / b=2.5, \quad \bar{\sigma}_{z} / q=0.07

 

Therefore, \sigma_{z}=4 \bar{\sigma}_{z}=4 \times 0.07 q=4 \times 0.07 \times 150=42 kN / m ^{2}.

6.5.
6.6

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