Bearing Capacity of Shallow Foundations

CIVL 451 – Foundation Engineering – Classroom Notes

Definitions

• For foundation design to be satisfactory three main principles must be satisfied;

– Shear failure of the soil carrying the foundation should be avoided,

– Excessive displacements should be avoided,

– Excessive differential settlements between individual foundations should be avoided.

Shear Failure Mechanisms

Terzaghi’s Bearing Capacity Theory

Terzaghi’s Bearing Capacity Theory

For GENERAL SHEAR FAILURE.

Terzaghi’s Bearing Capacity Theory

• Bearing capacity factors for General Shear Failure equations;

Terzaghi’s Bearing Capacity Theory

• For Local Shear Failure;

Global Factor of Safety

• In order to ensure that excessive displacements are avoided, a factor of safety (FS) can be applied on the estimated ultimate bearing capacity such that;

• However, this is a lump sum factor and it does not necessarily guarantee that the allowable settlement criteria will be satisfied. Independent settlement calculations should be carried out to provide an explicit check on the predicted settlement.

• Traditionally, FS is used as 3 for shallow foundations. Eurocode 7 advise factoring parameters used in the calculations as well as the applied loads.

Terzaghi’s Bearing Capacity Theory

Effect of Water Table

• The effect of water table on the bearing capacity can be considered as;

Exercises

Reference: B.M. Das, Principles of Foundation Engineering, Thomson – Brooks/Cole.