Subgrade Modulus

[Lutfi]

I have a question, lets say I have a site with K = 250 PCI, then compact the soil to 98% up to 12 deep, then on top of that I place 8 inches of lime rock compacted to LBR 100. What would the new K value be? Or does it stay the same?

 

[Focht3]

Why do you want a subgrade modulus value? Is this for a pavement design, spread footing - or mat foundation for a 40+ story office building? I'd suggest that you do a search of [green]Eng-Tips[/green] for some very good discussions of subgrade modulus and plate load tests.

In a nutshell, there's no such thing as "the" k-value. The use of k=250 pci suggests a paving design - it's too high for spread footings, strip footings or a mat on "normal" soils. If the site has a k-value that high, you shouldn't recompact the disturbed surface soils because that would be weaker than the underlying material - you'd replace it with a crushed rock, preferably a crushed granite or schist. Would the compacted layer affect the k-value? Yes. How much? That depends entirely on the size of the loaded are compared to the thicknesses of the various layers -



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora.