Converting a CBR Value into a Modulus of Subgrade Reaction

[ih8xc]

As the title states I am looking to convert the CBR value of a poorly graded sand and gravel into a modulus of subgrade reaction to be used in foundation design (not pavement design). I have found some information related to this while searching through this forum and others, however I am finding it difficult to find specific references for CBR to k for foundations.

The average CBR for the material at 95% Modified Proctor density is 30 (measured at 0.2").

 

[dicksewerrat]

Here is a diagram from Army Corps of Engineers and one other one but don't know the origin

Richard A. Cornelius, P.E.
WWW.amlinereast.com

 

[dicksewerrat]

The other one

Richard A. Cornelius, P.E.
WWW.amlinereast.com

 

[Okiryu]

I think that CBR is used for pavement design and therefore you will find that the correlations to K-values are more related to pavements and slabs-on-grade. I saw K-values for foundations which the main parameter is the soil modulus (E).

 

[Ron]

Agree with Okiryu....

The "k" value used for foundation design is about 1/4 of the "k" used for pavement design.

A "k" value of 50pci is actually a relatively high value, whereas a "k" value for pavement modulus of subgrade reaction would be on the order of 150 to 200, in similar soils.

 

[Okiryu]

Ron, is that difference due to the size of the plate when doing plate bearing tests in order to obtain "k"? (30" vs. 12" plate sizes)

 

[Ron]

Okiryu...actually the 12" plate will result in a higher "k" value.

 

[Okiryu]

Hi Ron, agree with you. In Japan we use this correlation between k30 and k12: k12 = 2.2 x k30