Soil Spring Constant 6

[geotechgal]

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.

 

[JAE]

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]

Thanks a ton that helps. Would U be able to give me a reference where I can read more about this.

 

[JAE]

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]

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