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geotechgal (Geotechnical) (OP)
2 Mar 05 18:12
Is the Soil Spring Constant the same as Modulus of Subgrade reacton? I argued with a collegue that it is not. Please tell me I am right! Can anyone give me references where I can get some info about Soil Spring Constant.
Helpful Member!(5)  JAE (Structural)
2 Mar 05 18:45
Modulus of subgrade reaction is a unit of pressure divided by a settlement - lbs/sq. in per inch of deflection.

So a modulus of 75 pci would mean that you have a soil that will deflect 1 inch for every 75 psi that's placed on it (I believe the standard is a 30 inch diameter test plate).

The "spring" that you use in a structural model supported by the soil would be a value of lbs/inch or kips/inch...where your spring would represent a particular area - say 1 square foot of a footing...

The spring value would then be:

75 pci x 1 sq. ft x (144 sq. in / sq. ft) = 10,800 lbs/inch

So if you had a 3' x 3' footing - you could use a grid of springs under the footing based on a presumed soil modulus.  The springs on the edges would have 1/2 the spring value, the springs on the corners would have 1/4, and the interiors would have full value.
geotechgal (Geotechnical) (OP)
2 Mar 05 18:50
Thanks a ton that helps. Would U be able to give me a reference where I can read more about this.
JAE (Structural)
2 Mar 05 18:58
I don't have a specific book - I have a chart that lays out various modulus values for different soil types and the rest is in the gray matter of my head.  Perhaps someone out there can point to something.
JAE (Structural)
2 Mar 05 19:01
Well - try this link - and click on section 2.3 in the upper right hand corner.

http://training.ce.washington.edu/WSDOT/Modules/04_design_parameters/04-2_body.htm#k

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