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(OP)
Hopefully this is an easy one.

I haven't seen this written anywhere, making me doubtful, but it seems that there be a strong correlation between k and f'c, if the subgrade is concrete. (in my case, the "foundation" is the plain concrete within a dam)  In fact, it seems like I should use f'c as k.

Am I missing something, or is this as simple as I'm thinking it is?

### RE: k - subgrade reaction

You might want to look at layered elastic analysis programs; these can handle multi-layered systems well.  Some state transportation departments can likely point you in the right direction.

Dik

### RE: k - subgrade reaction

Not sure exactly what you mean.  I've seen a "modulus of subgrade reaction", IE, the elastic constant for an elastic foundation problem.  The constant in that case will have units of, say, lbs/sq ft/ft, IE, pressure / deflection, and not just pressure.  That would be fairly unrelated to concrete break strength, fc' (in the same way that modulus of elasticity for steel is unrelated to yield strength).

There are also problems formulated for a semi-infinite solid, and you should be able to get an idea of the local deflection from that type of formulation.  Roark's Formulas for Stress and  Strain may have info on that topic.  I've seen it somewhere!

If bearing is very high, also check ACI 318 for bearing pressure limitations (which is based on fc', but not related to deflection).

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