Computer · Soil Mechanics

Assuming individual soil layers to be isotropic and homogeneous, what is the equivalent coefficient of permeability for flow occurring in the direction perpendicular to the bedding planes (vertical flow) for a three-layered soil system? (where K1, K2, K3 are permeabilities and H1, H2, H3 are layer thicknesses, and H = H1 + H2 + H3)