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# Horizontal Subgrade Reaction - Divided by Pile Diameter

## Horizontal Subgrade Reaction - Divided by Pile Diameter

(OP)
I have commmonly seen horizontal subgrade reaction be given as a number, to be divided by pile diameter. This is then multiplied by pile diameter to get the horizontal stiffness. Does this make sense, that an 8" pile see the same soil stiffness as a 3' pile, or am I interpreting this wrong?

### RE: Horizontal Subgrade Reaction - Divided by Pile Diameter

If you have a horizontal subgrade reaction of say 50 pci, what we do is multiply a 12" vertical segment of the pile and the pile diameter to get a spring which is applied to nodes at 12" o.c. up the pile length in our analysis model.

So if you have an 8" pile:

50 pci x 8" x 12" = 4,800 lbs/inch spring

This is very rudimentary but is used in structural models across a range (a parametric approach) - say 25 pci to 100 pci - to achieve a bracketed design.

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### RE: Horizontal Subgrade Reaction - Divided by Pile Diameter

(OP)
Fairly familiar with the design of foundations - but this geotech has given me subgrade reaction as units of force per volume divided by pile diameter (pfc/d) for subgrade modulus.

### RE: Horizontal Subgrade Reaction - Divided by Pile Diameter

That is weird

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