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Soil Mechanics and Foundation Engineering - Engineering

Q1:

If L and B are the length and breadth of a footing, e the eccentricity along the length and P and Q are the axial force and bearing capacity of the soil, then, to avoid tension,

A

B

C

D

ANS:A -

Bearing capacity of soil= Axial stress + Bending Stress.
Q = P/A + M/Z.
Where, M= Moment = P * e.
Z= Section Modulus = BL^2/6 [For rectangular footing].
Therefore, Q = P/(BL) + Pe/(BL^2/6),
Q = P/(BL) + 6Pe/(BL^2),
Q = P/(BL)* [1+6e/L],
BL = P/Q*[1+6e/L]. In option C, If e is too large tension will develop on the footing. Therefore A is the answer. No chance of tension development.

We get two equations when we write stress balancing equation under the footing. One is A and the other is C.

So, the answer is A.