In expansive soils, drilled piers are subjected to

A) a downward force in the expansive region of the soil, which generally occurs
well below the ground surface.

B) an uplift force in the expansive region of the soil, which generally occurs well
below the ground surface.

c) an uplift force in the expansive region of the soil, which generally occurs in
the upper soil layer.

D) Any one of these, depending on the local geology.