Questions about Bearing Capacity formula

[LearnerN]

I have a couple questions about the Terzaghi-Meyerhof equation for bearing capacity.

(1) This equation has a variable p-sub-q that is an additional surface surcharge. What is the difference between a surface surcharge and a load on the footing? What are some examples of an additional surface surcharge?

(2) Dumb question. Why is a surface surcharge load added to the equation resulting in a higher bearing capacity? I'm trying to understand this conceptually.

Thank you!

 

[GeoPaveTraffic]

You need to remember that these bearing capacity equations are for failure of the soil beneath the footing. The surface surcharge helps resist the movement of soil upperward from beneath the footing. Since that surcharge is resisting the failure, it increases the capacity.

This is the same effect as the increase in the bearing capacity you see when the footing is deeper below the ground surface, assuming everything else is the same.

Mike Lambert