Bearing Capacity - Terzaghi's Bearing Capacity Theory

Terzaghi's Bearing Capacity Theory

Karl von Terzaghi was the first to present a comprehensive theory for the evaluation of the ultimate bearing capacity of rough shallow foundations. This theory states that a foundation is shallow if its depth is less than or equal to its width. Later investigations, however, have suggested that foundations with a depth, measured from the ground surface, equal to 3 to 4 times their width may be defined as shallow foundations(Das, 2007).

Terzaghi developed a method for determining bearing capacity for the general shear failure case in 1943. The equations are given below.

For square foundations:

For continuous foundations:

For circular foundations:

where

for φ' = 0

for φ' > 0

c′ is the effective cohesion.

σ_zD′ is the vertical effective stress at the depth the foundation is laid.

γ′ is the effective unit weight when saturated or the total unit weight when not fully saturated.

B is the width or the diameter of the foundation.

φ′ is the effective internal angle of friction.

K_pγ is obtained graphically. Simplifications have been made to eliminate the need for K_pγ. One such was done by Coduto, given below, and it is accurate to within 10%.

For foundations that exhibit the local shear failure mode in soils, Terzaghi suggested the following modifications to the previous equations. The equations are given below.

For square foundations:

For continuous foundations:

For circular foundations:

, the modified bearing capacity factors, can be calculated by using the bearing capacity factors equations(for, respectively) by replacing the effective internal angle of friction by a value equal to