Shallow Foundation Depth

[NBRY1]

At what depth are the shallow foundation bearing capacity theories valid?
Terzaghi assumed D < B; however, what is the assumption if using Meyerhoff Bearing Capacity Theory?

 

[GeoEnvGuy]

Terzaghi published relationships for general (B> Df) and local shear (B<Df). Meyerhof provided a theory that is applicable to shallow and deep foundations. Vesic conducted tests on sand to determine the type of failure expected summarized in the image below where the Df is the depth of foundation and R is the area divided by the perimeter. So a 1 m by 3 m foundation and at 80% relative density can be expected to have a general shear down to 32 metres.

 

[NBRY1]

not sure your math is right, but thanks for the comments.
Looks like depth could go to ~4 meters or so; but surely not 32m??

 

[r13]

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.[2] 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.[2]...

In 1951, Meyerhof published a bearing capacity theory which could be applied to rough shallow and deep foundations.[3]

[2] Das, Braja M (2007). Principles of foundation engineering (6th ed.). Toronto, Ontario, Canada: Thomson.
[3] Das, Braja M (1999). Shallow foundations : bearing capacity and settlement. Boca Raton, FL: CRC Press.